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href="#incremental-encoding-and-decoding">Incremental Encoding and Decoding</a><ul>112<li><a class="reference internal" href="#incrementalencoder-objects">IncrementalEncoder Objects</a></li>113<li><a class="reference internal" href="#incrementaldecoder-objects">IncrementalDecoder Objects</a></li>114</ul>115</li>116<li><a class="reference internal" href="#stream-encoding-and-decoding">Stream Encoding and Decoding</a><ul>117<li><a class="reference internal" href="#streamwriter-objects">StreamWriter Objects</a></li>118<li><a class="reference internal" href="#streamreader-objects">StreamReader Objects</a></li>119<li><a class="reference internal" href="#streamreaderwriter-objects">StreamReaderWriter Objects</a></li>120<li><a class="reference internal" href="#streamrecoder-objects">StreamRecoder Objects</a></li>121</ul>122</li>123</ul>124</li>125<li><a class="reference internal" href="#encodings-and-unicode">Encodings and Unicode</a></li>126<li><a class="reference internal" href="#standard-encodings">Standard Encodings</a></li>127<li><a class="reference internal" href="#python-specific-encodings">Python Specific Encodings</a><ul>128<li><a class="reference internal" href="#text-encodings">Text Encodings</a></li>129<li><a class="reference internal" href="#binary-transforms">Binary Transforms</a></li>130<li><a class="reference internal" href="#standalone-codec-functions">Standalone Codec Functions</a></li>131<li><a class="reference internal" href="#text-transforms">Text Transforms</a></li>132</ul>133</li>134<li><a class="reference internal" href="#module-encodings"><code class="xref py py-mod docutils literal notranslate"><span class="pre">encodings</span></code> — Encodings package</a></li>135<li><a class="reference internal" href="#module-encodings.idna"><code class="xref py py-mod docutils literal notranslate"><span class="pre">encodings.idna</span></code> — Internationalized Domain Names in Applications</a></li>136<li><a class="reference internal" href="#module-encodings.mbcs"><code class="xref py py-mod docutils literal notranslate"><span class="pre">encodings.mbcs</span></code> — Windows ANSI codepage</a></li>137<li><a class="reference internal" href="#module-encodings.utf_8_sig"><code class="xref py py-mod docutils literal notranslate"><span class="pre">encodings.utf_8_sig</span></code> — UTF-8 codec with BOM signature</a></li>138</ul>139</li>140</ul>141 142  </div>143  <div>144    <h4>Previous topic</h4>145    <p class="topless"><a href="struct.html"146                          title="previous chapter"><code class="xref py py-mod docutils literal notranslate"><span class="pre">struct</span></code> — Interpret bytes as packed binary data</a></p>147  </div>148  <div>149    <h4>Next topic</h4>150    <p class="topless"><a href="datatypes.html"151                          title="next chapter">Data Types</a></p>152  </div>153  <script>154    document.addEventListener('DOMContentLoaded', () => {155        const title = 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        <li class="switchers">204            <div class="language_switcher_placeholder"></div>205            <div class="version_switcher_placeholder"></div>206          </li>207          <li>208              209          </li>210    <li id="cpython-language-and-version">211      <a href="../index.html">3.15.0a6 Documentation</a> &#187;212    </li>213 214          <li class="nav-item nav-item-1"><a href="index.html" >The Python Standard Library</a> &#187;</li>215          <li class="nav-item nav-item-2"><a href="binary.html" accesskey="U">Binary Data Services</a> &#187;</li>216        <li class="nav-item nav-item-this"><a href=""><code class="xref py py-mod docutils literal notranslate"><span class="pre">codecs</span></code> — Codec registry and base classes</a></li>217                <li class="right">218                    219 220    <div class="inline-search" role="search">221        <form class="inline-search" action="../search.html" method="get">222          <input 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class="headerlink" href="#module-codecs" title="Link to this heading">¶</a></h1>248<p><strong>Source code:</strong> <a class="extlink-source reference external" href="https://github.com/python/cpython/tree/main/Lib/codecs.py">Lib/codecs.py</a></p>249<hr class="docutils" id="index-0" />250<p>This module defines base classes for standard Python codecs (encoders and251decoders) and provides access to the internal Python codec registry, which252manages the codec and error handling lookup process. Most standard codecs253are <a class="reference internal" href="../glossary.html#term-text-encoding"><span class="xref std std-term">text encodings</span></a>, which encode text to bytes (and254decode bytes to text), but there are also codecs provided that encode text to255text, and bytes to bytes. Custom codecs may encode and decode between arbitrary256types, but some module features are restricted to be used specifically with257<span class="xref std std-term">text encodings</span> or with codecs that encode to258<a class="reference internal" href="stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code></a>.</p>259<p>The module defines the following functions for encoding and decoding with260any codec:</p>261<dl class="py function">262<dt class="sig sig-object py" id="codecs.encode">263<span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">encode</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">obj</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">encoding</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">'utf-8'</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">errors</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">'strict'</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.encode" title="Link to this definition">¶</a></dt>264<dd><p>Encodes <em>obj</em> using the codec registered for <em>encoding</em>.</p>265<p><em>Errors</em> may be given to set the desired error handling scheme. The266default error handler is <code class="docutils literal notranslate"><span class="pre">'strict'</span></code> meaning that encoding errors raise267<a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> (or a more codec specific subclass, such as268<a class="reference internal" href="exceptions.html#UnicodeEncodeError" title="UnicodeEncodeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">UnicodeEncodeError</span></code></a>). Refer to <a class="reference internal" href="#codec-base-classes"><span class="std std-ref">Codec Base Classes</span></a> for more269information on codec error handling.</p>270</dd></dl>271 272<dl class="py function">273<dt class="sig sig-object py" id="codecs.decode">274<span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">decode</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">obj</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">encoding</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">'utf-8'</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">errors</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">'strict'</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.decode" title="Link to this definition">¶</a></dt>275<dd><p>Decodes <em>obj</em> using the codec registered for <em>encoding</em>.</p>276<p><em>Errors</em> may be given to set the desired error handling scheme. The277default error handler is <code class="docutils literal notranslate"><span class="pre">'strict'</span></code> meaning that decoding errors raise278<a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> (or a more codec specific subclass, such as279<a class="reference internal" href="exceptions.html#UnicodeDecodeError" title="UnicodeDecodeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">UnicodeDecodeError</span></code></a>). Refer to <a class="reference internal" href="#codec-base-classes"><span class="std std-ref">Codec Base Classes</span></a> for more280information on codec error handling.</p>281</dd></dl>282 283<dl class="py function">284<dt class="sig sig-object py" id="codecs.charmap_build">285<span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">charmap_build</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">string</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.charmap_build" title="Link to this definition">¶</a></dt>286<dd><p>Return a mapping suitable for encoding with a custom single-byte encoding.287Given a <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a> <em>string</em> of up to 256 characters representing a288decoding table, returns either a compact internal mapping object289<code class="docutils literal notranslate"><span class="pre">EncodingMap</span></code> or a <a class="reference internal" href="stdtypes.html#dict" title="dict"><code class="xref py py-class docutils literal notranslate"><span class="pre">dictionary</span></code></a> mapping character ordinals290to byte values. Raises a <a class="reference internal" href="exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a> on invalid input.</p>291</dd></dl>292 293<p>The full details for each codec can also be looked up directly:</p>294<dl class="py function">295<dt class="sig sig-object py" id="codecs.lookup">296<span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">lookup</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">encoding</span></span></em>, <em class="sig-param"><span class="positional-only-separator o"><abbr title="Positional-only parameter separator (PEP 570)"><span class="pre">/</span></abbr></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.lookup" title="Link to this definition">¶</a></dt>297<dd><p>Looks up the codec info in the Python codec registry and returns a298<a class="reference internal" href="#codecs.CodecInfo" title="codecs.CodecInfo"><code class="xref py py-class docutils literal notranslate"><span class="pre">CodecInfo</span></code></a> object as defined below.</p>299<p>This function first normalizes the <em>encoding</em>: all ASCII letters are300converted to lower case, spaces are replaced with hyphens.301Then encoding is looked up in the registry’s cache. If not found, the list of302registered search functions is scanned. If no <a class="reference internal" href="#codecs.CodecInfo" title="codecs.CodecInfo"><code class="xref py py-class docutils literal notranslate"><span class="pre">CodecInfo</span></code></a> object is303found, a <a class="reference internal" href="exceptions.html#LookupError" title="LookupError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">LookupError</span></code></a> is raised. Otherwise, the <code class="xref py py-class docutils literal notranslate"><span class="pre">CodecInfo</span></code> object304is stored in the cache and returned to the caller.</p>305<div class="versionchanged">306<p><span class="versionmodified changed">Changed in version 3.9: </span>Any characters except ASCII letters and digits and a dot are converted to underscore.</p>307</div>308<div class="versionchanged">309<p><span class="versionmodified changed">Changed in version 3.15: </span>No characters are converted to underscore anymore.310Spaces are converted to hyphens.</p>311</div>312</dd></dl>313 314<dl class="py class">315<dt class="sig sig-object py" id="codecs.CodecInfo">316<em class="property"><span class="k"><span class="pre">class</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">CodecInfo</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">encode</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">decode</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">streamreader</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">streamwriter</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">incrementalencoder</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">incrementaldecoder</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">name</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.CodecInfo" title="Link to this definition">¶</a></dt>317<dd><p>Codec details when looking up the codec registry. The constructor318arguments are stored in attributes of the same name:</p>319<dl class="py attribute">320<dt class="sig sig-object py" id="codecs.CodecInfo.name">321<span class="sig-name descname"><span class="pre">name</span></span><a class="headerlink" href="#codecs.CodecInfo.name" title="Link to this definition">¶</a></dt>322<dd><p>The name of the encoding.</p>323</dd></dl>324 325<dl class="py attribute">326<dt class="sig sig-object py" id="codecs.CodecInfo.encode">327<span class="sig-name descname"><span class="pre">encode</span></span><a class="headerlink" href="#codecs.CodecInfo.encode" title="Link to this definition">¶</a></dt>328<dt class="sig sig-object py" id="codecs.CodecInfo.decode">329<span class="sig-name descname"><span class="pre">decode</span></span><a class="headerlink" href="#codecs.CodecInfo.decode" title="Link to this definition">¶</a></dt>330<dd><p>The stateless encoding and decoding functions. These must be331functions or methods which have the same interface as332the <a class="reference internal" href="#codecs.Codec.encode" title="codecs.Codec.encode"><code class="xref py py-meth docutils literal notranslate"><span class="pre">encode()</span></code></a> and <a class="reference internal" href="#codecs.Codec.decode" title="codecs.Codec.decode"><code class="xref py py-meth docutils literal notranslate"><span class="pre">decode()</span></code></a> methods of Codec333instances (see <a class="reference internal" href="#codec-objects"><span class="std std-ref">Codec Interface</span></a>).334The functions or methods are expected to work in a stateless mode.</p>335</dd></dl>336 337<dl class="py attribute">338<dt class="sig sig-object py" id="codecs.CodecInfo.incrementalencoder">339<span class="sig-name descname"><span class="pre">incrementalencoder</span></span><a class="headerlink" href="#codecs.CodecInfo.incrementalencoder" title="Link to this definition">¶</a></dt>340<dt class="sig sig-object py" id="codecs.CodecInfo.incrementaldecoder">341<span class="sig-name descname"><span class="pre">incrementaldecoder</span></span><a class="headerlink" href="#codecs.CodecInfo.incrementaldecoder" title="Link to this definition">¶</a></dt>342<dd><p>Incremental encoder and decoder classes or factory functions.343These have to provide the interface defined by the base classes344<a class="reference internal" href="#codecs.IncrementalEncoder" title="codecs.IncrementalEncoder"><code class="xref py py-class docutils literal notranslate"><span class="pre">IncrementalEncoder</span></code></a> and <a class="reference internal" href="#codecs.IncrementalDecoder" title="codecs.IncrementalDecoder"><code class="xref py py-class docutils literal notranslate"><span class="pre">IncrementalDecoder</span></code></a>,345respectively. Incremental codecs can maintain state.</p>346</dd></dl>347 348<dl class="py attribute">349<dt class="sig sig-object py" id="codecs.CodecInfo.streamwriter">350<span class="sig-name descname"><span class="pre">streamwriter</span></span><a class="headerlink" href="#codecs.CodecInfo.streamwriter" title="Link to this definition">¶</a></dt>351<dt class="sig sig-object py" id="codecs.CodecInfo.streamreader">352<span class="sig-name descname"><span class="pre">streamreader</span></span><a class="headerlink" href="#codecs.CodecInfo.streamreader" title="Link to this definition">¶</a></dt>353<dd><p>Stream writer and reader classes or factory functions. These have to354provide the interface defined by the base classes355<a class="reference internal" href="#codecs.StreamWriter" title="codecs.StreamWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamWriter</span></code></a> and <a class="reference internal" href="#codecs.StreamReader" title="codecs.StreamReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReader</span></code></a>, respectively.356Stream codecs can maintain state.</p>357</dd></dl>358 359</dd></dl>360 361<p>To simplify access to the various codec components, the module provides362these additional functions which use <a class="reference internal" href="#codecs.lookup" title="codecs.lookup"><code class="xref py py-func docutils literal notranslate"><span class="pre">lookup()</span></code></a> for the codec lookup:</p>363<dl class="py function">364<dt class="sig sig-object py" id="codecs.getencoder">365<span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">getencoder</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">encoding</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.getencoder" title="Link to this definition">¶</a></dt>366<dd><p>Look up the codec for the given encoding and return its encoder function.</p>367<p>Raises a <a class="reference internal" href="exceptions.html#LookupError" title="LookupError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">LookupError</span></code></a> in case the encoding cannot be found.</p>368</dd></dl>369 370<dl class="py function">371<dt class="sig sig-object py" id="codecs.getdecoder">372<span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">getdecoder</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">encoding</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.getdecoder" title="Link to this definition">¶</a></dt>373<dd><p>Look up the codec for the given encoding and return its decoder function.</p>374<p>Raises a <a class="reference internal" href="exceptions.html#LookupError" title="LookupError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">LookupError</span></code></a> in case the encoding cannot be found.</p>375</dd></dl>376 377<dl class="py function">378<dt class="sig sig-object py" id="codecs.getincrementalencoder">379<span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">getincrementalencoder</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">encoding</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.getincrementalencoder" title="Link to this definition">¶</a></dt>380<dd><p>Look up the codec for the given encoding and return its incremental encoder381class or factory function.</p>382<p>Raises a <a class="reference internal" href="exceptions.html#LookupError" title="LookupError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">LookupError</span></code></a> in case the encoding cannot be found or the codec383doesn’t support an incremental encoder.</p>384</dd></dl>385 386<dl class="py function">387<dt class="sig sig-object py" id="codecs.getincrementaldecoder">388<span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">getincrementaldecoder</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">encoding</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.getincrementaldecoder" title="Link to this definition">¶</a></dt>389<dd><p>Look up the codec for the given encoding and return its incremental decoder390class or factory function.</p>391<p>Raises a <a class="reference internal" href="exceptions.html#LookupError" title="LookupError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">LookupError</span></code></a> in case the encoding cannot be found or the codec392doesn’t support an incremental decoder.</p>393</dd></dl>394 395<dl class="py function">396<dt class="sig sig-object py" id="codecs.getreader">397<span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">getreader</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">encoding</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.getreader" title="Link to this definition">¶</a></dt>398<dd><p>Look up the codec for the given encoding and return its <a class="reference internal" href="#codecs.StreamReader" title="codecs.StreamReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReader</span></code></a>399class or factory function.</p>400<p>Raises a <a class="reference internal" href="exceptions.html#LookupError" title="LookupError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">LookupError</span></code></a> in case the encoding cannot be found.</p>401</dd></dl>402 403<dl class="py function">404<dt class="sig sig-object py" id="codecs.getwriter">405<span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">getwriter</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">encoding</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.getwriter" title="Link to this definition">¶</a></dt>406<dd><p>Look up the codec for the given encoding and return its <a class="reference internal" href="#codecs.StreamWriter" title="codecs.StreamWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamWriter</span></code></a>407class or factory function.</p>408<p>Raises a <a class="reference internal" href="exceptions.html#LookupError" title="LookupError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">LookupError</span></code></a> in case the encoding cannot be found.</p>409</dd></dl>410 411<p>Custom codecs are made available by registering a suitable codec search412function:</p>413<dl class="py function">414<dt class="sig sig-object py" id="codecs.register">415<span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">register</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">search_function</span></span></em>, <em class="sig-param"><span class="positional-only-separator o"><abbr title="Positional-only parameter separator (PEP 570)"><span class="pre">/</span></abbr></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.register" title="Link to this definition">¶</a></dt>416<dd><p>Register a codec search function. Search functions are expected to take one417argument, being the encoding name in all lower case letters with spaces418converted to hyphens, and return a <a class="reference internal" href="#codecs.CodecInfo" title="codecs.CodecInfo"><code class="xref py py-class docutils literal notranslate"><span class="pre">CodecInfo</span></code></a> object.419In case a search function cannot find a given encoding, it should return420<code class="docutils literal notranslate"><span class="pre">None</span></code>.</p>421</dd></dl>422 423<dl class="py function">424<dt class="sig sig-object py" id="codecs.unregister">425<span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">unregister</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">search_function</span></span></em>, <em class="sig-param"><span class="positional-only-separator o"><abbr title="Positional-only parameter separator (PEP 570)"><span class="pre">/</span></abbr></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.unregister" title="Link to this definition">¶</a></dt>426<dd><p>Unregister a codec search function and clear the registry’s cache.427If the search function is not registered, do nothing.</p>428<div class="versionadded">429<p><span class="versionmodified added">Added in version 3.10.</span></p>430</div>431</dd></dl>432 433<p>While the builtin <a class="reference internal" href="functions.html#open" title="open"><code class="xref py py-func docutils literal notranslate"><span class="pre">open()</span></code></a> and the associated <a class="reference internal" href="io.html#module-io" title="io: Core tools for working with streams."><code class="xref py py-mod docutils literal notranslate"><span class="pre">io</span></code></a> module are the434recommended approach for working with encoded text files, this module435provides additional utility functions and classes that allow the use of a436wider range of codecs when working with binary files:</p>437<dl class="py function">438<dt class="sig sig-object py" id="codecs.open">439<span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">open</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">filename</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">mode</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">'r'</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">encoding</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">errors</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">'strict'</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">buffering</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">-1</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.open" title="Link to this definition">¶</a></dt>440<dd><p>Open an encoded file using the given <em>mode</em> and return an instance of441<a class="reference internal" href="#codecs.StreamReaderWriter" title="codecs.StreamReaderWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReaderWriter</span></code></a>, providing transparent encoding/decoding.442The default file mode is <code class="docutils literal notranslate"><span class="pre">'r'</span></code>, meaning to open the file in read mode.</p>443<div class="admonition note">444<p class="admonition-title">Note</p>445<p>If <em>encoding</em> is not <code class="docutils literal notranslate"><span class="pre">None</span></code>, then the446underlying encoded files are always opened in binary mode.447No automatic conversion of <code class="docutils literal notranslate"><span class="pre">'\n'</span></code> is done on reading and writing.448The <em>mode</em> argument may be any binary mode acceptable to the built-in449<code class="xref py py-func docutils literal notranslate"><span class="pre">open()</span></code> function; the <code class="docutils literal notranslate"><span class="pre">'b'</span></code> is automatically added.</p>450</div>451<p><em>encoding</em> specifies the encoding which is to be used for the file.452Any encoding that encodes to and decodes from bytes is allowed, and453the data types supported by the file methods depend on the codec used.</p>454<p><em>errors</em> may be given to define the error handling. It defaults to <code class="docutils literal notranslate"><span class="pre">'strict'</span></code>455which causes a <a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> to be raised in case an encoding error occurs.</p>456<p><em>buffering</em> has the same meaning as for the built-in <code class="xref py py-func docutils literal notranslate"><span class="pre">open()</span></code> function.457It defaults to -1 which means that the default buffer size will be used.</p>458<div class="versionchanged">459<p><span class="versionmodified changed">Changed in version 3.11: </span>The <code class="docutils literal notranslate"><span class="pre">'U'</span></code> mode has been removed.</p>460</div>461<div class="deprecated">462<p><span class="versionmodified deprecated">Deprecated since version 3.14: </span><a class="reference internal" href="#codecs.open" title="codecs.open"><code class="xref py py-func docutils literal notranslate"><span class="pre">codecs.open()</span></code></a> has been superseded by <code class="xref py py-func docutils literal notranslate"><span class="pre">open()</span></code>.</p>463</div>464</dd></dl>465 466<dl class="py function">467<dt class="sig sig-object py" id="codecs.EncodedFile">468<span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">EncodedFile</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">file</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">data_encoding</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">file_encoding</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">errors</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">'strict'</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.EncodedFile" title="Link to this definition">¶</a></dt>469<dd><p>Return a <a class="reference internal" href="#codecs.StreamRecoder" title="codecs.StreamRecoder"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamRecoder</span></code></a> instance, a wrapped version of <em>file</em>470which provides transparent transcoding. The original file is closed471when the wrapped version is closed.</p>472<p>Data written to the wrapped file is decoded according to the given473<em>data_encoding</em> and then written to the original file as bytes using474<em>file_encoding</em>. Bytes read from the original file are decoded475according to <em>file_encoding</em>, and the result is encoded476using <em>data_encoding</em>.</p>477<p>If <em>file_encoding</em> is not given, it defaults to <em>data_encoding</em>.</p>478<p><em>errors</em> may be given to define the error handling. It defaults to479<code class="docutils literal notranslate"><span class="pre">'strict'</span></code>, which causes <a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> to be raised in case an encoding480error occurs.</p>481</dd></dl>482 483<dl class="py function">484<dt class="sig sig-object py" id="codecs.iterencode">485<span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">iterencode</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">iterator</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">encoding</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">errors</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">'strict'</span></span></em>, <em class="sig-param"><span class="o"><span class="pre">**</span></span><span class="n"><span class="pre">kwargs</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.iterencode" title="Link to this definition">¶</a></dt>486<dd><p>Uses an incremental encoder to iteratively encode the input provided by487<em>iterator</em>. <em>iterator</em> must yield <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a> objects.488This function is a <a class="reference internal" href="../glossary.html#term-generator"><span class="xref std std-term">generator</span></a>. The <em>errors</em> argument (as well as any489other keyword argument) is passed through to the incremental encoder.</p>490<p>This function requires that the codec accept text <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a> objects491to encode. Therefore it does not support bytes-to-bytes encoders such as492<code class="docutils literal notranslate"><span class="pre">base64_codec</span></code>.</p>493</dd></dl>494 495<dl class="py function">496<dt class="sig sig-object py" id="codecs.iterdecode">497<span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">iterdecode</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">iterator</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">encoding</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">errors</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">'strict'</span></span></em>, <em class="sig-param"><span class="o"><span class="pre">**</span></span><span class="n"><span class="pre">kwargs</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.iterdecode" title="Link to this definition">¶</a></dt>498<dd><p>Uses an incremental decoder to iteratively decode the input provided by499<em>iterator</em>. <em>iterator</em> must yield <a class="reference internal" href="stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code></a> objects.500This function is a <a class="reference internal" href="../glossary.html#term-generator"><span class="xref std std-term">generator</span></a>. The <em>errors</em> argument (as well as any501other keyword argument) is passed through to the incremental decoder.</p>502<p>This function requires that the codec accept <a class="reference internal" href="stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code></a> objects503to decode. Therefore it does not support text-to-text encoders such as504<code class="docutils literal notranslate"><span class="pre">rot_13</span></code>, although <code class="docutils literal notranslate"><span class="pre">rot_13</span></code> may be used equivalently with505<a class="reference internal" href="#codecs.iterencode" title="codecs.iterencode"><code class="xref py py-func docutils literal notranslate"><span class="pre">iterencode()</span></code></a>.</p>506</dd></dl>507 508<dl class="py function">509<dt class="sig sig-object py" id="codecs.readbuffer_encode">510<span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">readbuffer_encode</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">buffer</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">errors</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="positional-only-separator o"><abbr title="Positional-only parameter separator (PEP 570)"><span class="pre">/</span></abbr></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.readbuffer_encode" title="Link to this definition">¶</a></dt>511<dd><p>Return a <a class="reference internal" href="stdtypes.html#tuple" title="tuple"><code class="xref py py-class docutils literal notranslate"><span class="pre">tuple</span></code></a> containing the raw bytes of <em>buffer</em>, a512<a class="reference internal" href="../c-api/buffer.html#bufferobjects"><span class="std std-ref">buffer-compatible object</span></a> or <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a>513(encoded to UTF-8 before processing), and their length in bytes.</p>514<p>The <em>errors</em> argument is ignored.</p>515<div class="highlight-pycon notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">codecs</span><span class="o">.</span><span class="n">readbuffer_encode</span><span class="p">(</span><span class="sa">b</span><span class="s2">&quot;Zito&quot;</span><span class="p">)</span>516<span class="go">(b&#39;Zito&#39;, 4)</span>517</pre></div>518</div>519</dd></dl>520 521<p>The module also provides the following constants which are useful for reading522and writing to platform dependent files:</p>523<dl class="py data">524<dt class="sig sig-object py" id="codecs.BOM">525<span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">BOM</span></span><a class="headerlink" href="#codecs.BOM" title="Link to this definition">¶</a></dt>526<dt class="sig sig-object py" id="codecs.BOM_BE">527<span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">BOM_BE</span></span><a class="headerlink" href="#codecs.BOM_BE" title="Link to this definition">¶</a></dt>528<dt class="sig sig-object py" id="codecs.BOM_LE">529<span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">BOM_LE</span></span><a class="headerlink" href="#codecs.BOM_LE" title="Link to this definition">¶</a></dt>530<dt class="sig sig-object py" id="codecs.BOM_UTF8">531<span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">BOM_UTF8</span></span><a class="headerlink" href="#codecs.BOM_UTF8" title="Link to this definition">¶</a></dt>532<dt class="sig sig-object py" id="codecs.BOM_UTF16">533<span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">BOM_UTF16</span></span><a class="headerlink" href="#codecs.BOM_UTF16" title="Link to this definition">¶</a></dt>534<dt class="sig sig-object py" id="codecs.BOM_UTF16_BE">535<span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">BOM_UTF16_BE</span></span><a class="headerlink" href="#codecs.BOM_UTF16_BE" title="Link to this definition">¶</a></dt>536<dt class="sig sig-object py" id="codecs.BOM_UTF16_LE">537<span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">BOM_UTF16_LE</span></span><a class="headerlink" href="#codecs.BOM_UTF16_LE" title="Link to this definition">¶</a></dt>538<dt class="sig sig-object py" id="codecs.BOM_UTF32">539<span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">BOM_UTF32</span></span><a class="headerlink" href="#codecs.BOM_UTF32" title="Link to this definition">¶</a></dt>540<dt class="sig sig-object py" id="codecs.BOM_UTF32_BE">541<span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">BOM_UTF32_BE</span></span><a class="headerlink" href="#codecs.BOM_UTF32_BE" title="Link to this definition">¶</a></dt>542<dt class="sig sig-object py" id="codecs.BOM_UTF32_LE">543<span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">BOM_UTF32_LE</span></span><a class="headerlink" href="#codecs.BOM_UTF32_LE" title="Link to this definition">¶</a></dt>544<dd><p>These constants define various byte sequences,545being Unicode byte order marks (BOMs) for several encodings. They are546used in UTF-16 and UTF-32 data streams to indicate the byte order used,547and in UTF-8 as a Unicode signature. <a class="reference internal" href="#codecs.BOM_UTF16" title="codecs.BOM_UTF16"><code class="xref py py-const docutils literal notranslate"><span class="pre">BOM_UTF16</span></code></a> is either548<a class="reference internal" href="#codecs.BOM_UTF16_BE" title="codecs.BOM_UTF16_BE"><code class="xref py py-const docutils literal notranslate"><span class="pre">BOM_UTF16_BE</span></code></a> or <a class="reference internal" href="#codecs.BOM_UTF16_LE" title="codecs.BOM_UTF16_LE"><code class="xref py py-const docutils literal notranslate"><span class="pre">BOM_UTF16_LE</span></code></a> depending on the platform’s549native byte order, <a class="reference internal" href="#codecs.BOM" title="codecs.BOM"><code class="xref py py-const docutils literal notranslate"><span class="pre">BOM</span></code></a> is an alias for <code class="xref py py-const docutils literal notranslate"><span class="pre">BOM_UTF16</span></code>,550<a class="reference internal" href="#codecs.BOM_LE" title="codecs.BOM_LE"><code class="xref py py-const docutils literal notranslate"><span class="pre">BOM_LE</span></code></a> for <code class="xref py py-const docutils literal notranslate"><span class="pre">BOM_UTF16_LE</span></code> and <a class="reference internal" href="#codecs.BOM_BE" title="codecs.BOM_BE"><code class="xref py py-const docutils literal notranslate"><span class="pre">BOM_BE</span></code></a> for551<code class="xref py py-const docutils literal notranslate"><span class="pre">BOM_UTF16_BE</span></code>. The others represent the BOM in UTF-8 and UTF-32552encodings.</p>553</dd></dl>554 555<section id="codec-base-classes">556<span id="id1"></span><h2>Codec Base Classes<a class="headerlink" href="#codec-base-classes" title="Link to this heading">¶</a></h2>557<p>The <code class="xref py py-mod docutils literal notranslate"><span class="pre">codecs</span></code> module defines a set of base classes which define the558interfaces for working with codec objects, and can also be used as the basis559for custom codec implementations.</p>560<p>Each codec has to define four interfaces to make it usable as codec in Python:561stateless encoder, stateless decoder, stream reader and stream writer. The562stream reader and writers typically reuse the stateless encoder/decoder to563implement the file protocols. Codec authors also need to define how the564codec will handle encoding and decoding errors.</p>565<section id="error-handlers">566<span id="surrogateescape"></span><span id="id2"></span><h3>Error Handlers<a class="headerlink" href="#error-handlers" title="Link to this heading">¶</a></h3>567<p>To simplify and standardize error handling, codecs may implement different568error handling schemes by accepting the <em>errors</em> string argument:</p>569<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="s1">&#39;German ß, ♬&#39;</span><span class="o">.</span><span class="n">encode</span><span class="p">(</span><span class="n">encoding</span><span class="o">=</span><span class="s1">&#39;ascii&#39;</span><span class="p">,</span> <span class="n">errors</span><span class="o">=</span><span class="s1">&#39;backslashreplace&#39;</span><span class="p">)</span>570<span class="go">b&#39;German \\xdf, \\u266c&#39;</span>571<span class="gp">&gt;&gt;&gt; </span><span class="s1">&#39;German ß, ♬&#39;</span><span class="o">.</span><span class="n">encode</span><span class="p">(</span><span class="n">encoding</span><span class="o">=</span><span class="s1">&#39;ascii&#39;</span><span class="p">,</span> <span class="n">errors</span><span class="o">=</span><span class="s1">&#39;xmlcharrefreplace&#39;</span><span class="p">)</span>572<span class="go">b&#39;German &amp;#223;, &amp;#9836;&#39;</span>573</pre></div>574</div>575<p id="index-1">The following error handlers can be used with all Python576<a class="reference internal" href="#standard-encodings"><span class="std std-ref">Standard Encodings</span></a> codecs:</p>577<table class="docutils align-default">578<thead>579<tr class="row-odd"><th class="head"><p>Value</p></th>580<th class="head"><p>Meaning</p></th>581</tr>582</thead>583<tbody>584<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">'strict'</span></code></p></td>585<td><p>Raise <a class="reference internal" href="exceptions.html#UnicodeError" title="UnicodeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">UnicodeError</span></code></a> (or a subclass),586this is the default. Implemented in587<a class="reference internal" href="#codecs.strict_errors" title="codecs.strict_errors"><code class="xref py py-func docutils literal notranslate"><span class="pre">strict_errors()</span></code></a>.</p></td>588</tr>589<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">'ignore'</span></code></p></td>590<td><p>Ignore the malformed data and continue without591further notice. Implemented in592<a class="reference internal" href="#codecs.ignore_errors" title="codecs.ignore_errors"><code class="xref py py-func docutils literal notranslate"><span class="pre">ignore_errors()</span></code></a>.</p></td>593</tr>594<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">'replace'</span></code></p></td>595<td><p>Replace with a replacement marker. On596encoding, use <code class="docutils literal notranslate"><span class="pre">?</span></code> (ASCII character). On597decoding, use <code class="docutils literal notranslate"><span class="pre">�</span></code> (U+FFFD, the official598REPLACEMENT CHARACTER). Implemented in599<a class="reference internal" href="#codecs.replace_errors" title="codecs.replace_errors"><code class="xref py py-func docutils literal notranslate"><span class="pre">replace_errors()</span></code></a>.</p></td>600</tr>601<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">'backslashreplace'</span></code></p></td>602<td><p>Replace with backslashed escape sequences.603On encoding, use hexadecimal form of Unicode604code point with formats <code class="samp docutils literal notranslate"><span class="pre">\x</span><em><span class="pre">hh</span></em></code>605<code class="samp docutils literal notranslate"><span class="pre">\u</span><em><span class="pre">xxxx</span></em></code> <code class="samp docutils literal notranslate"><span class="pre">\U</span><em><span class="pre">xxxxxxxx</span></em></code>.606On decoding, use hexadecimal form of byte607value with format <code class="samp docutils literal notranslate"><span class="pre">\x</span><em><span class="pre">hh</span></em></code>.608Implemented in609<a class="reference internal" href="#codecs.backslashreplace_errors" title="codecs.backslashreplace_errors"><code class="xref py py-func docutils literal notranslate"><span class="pre">backslashreplace_errors()</span></code></a>.</p></td>610</tr>611<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">'surrogateescape'</span></code></p></td>612<td><p>On decoding, replace byte with individual613surrogate code ranging from <code class="docutils literal notranslate"><span class="pre">U+DC80</span></code> to614<code class="docutils literal notranslate"><span class="pre">U+DCFF</span></code>. This code will then be turned615back into the same byte when the616<code class="docutils literal notranslate"><span class="pre">'surrogateescape'</span></code> error handler is used617when encoding the data. (See <span class="target" id="index-2"></span><a class="pep reference external" href="https://peps.python.org/pep-0383/"><strong>PEP 383</strong></a> for618more.)</p></td>619</tr>620</tbody>621</table>622<p id="index-3">The following error handlers are only applicable to encoding (within623<a class="reference internal" href="../glossary.html#term-text-encoding"><span class="xref std std-term">text encodings</span></a>):</p>624<table class="docutils align-default">625<thead>626<tr class="row-odd"><th class="head"><p>Value</p></th>627<th class="head"><p>Meaning</p></th>628</tr>629</thead>630<tbody>631<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">'xmlcharrefreplace'</span></code></p></td>632<td><p>Replace with XML/HTML numeric character633reference, which is a decimal form of Unicode634code point with format <code class="samp docutils literal notranslate"><span class="pre">&amp;#</span><em><span class="pre">num</span></em><span class="pre">;</span></code>.635Implemented in636<a class="reference internal" href="#codecs.xmlcharrefreplace_errors" title="codecs.xmlcharrefreplace_errors"><code class="xref py py-func docutils literal notranslate"><span class="pre">xmlcharrefreplace_errors()</span></code></a>.</p></td>637</tr>638<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">'namereplace'</span></code></p></td>639<td><p>Replace with <code class="docutils literal notranslate"><span class="pre">\N{...}</span></code> escape sequences,640what appears in the braces is the Name641property from Unicode Character Database.642Implemented in <a class="reference internal" href="#codecs.namereplace_errors" title="codecs.namereplace_errors"><code class="xref py py-func docutils literal notranslate"><span class="pre">namereplace_errors()</span></code></a>.</p></td>643</tr>644</tbody>645</table>646<p id="index-4">In addition, the following error handler is specific to the given codecs:</p>647<table class="docutils align-default">648<thead>649<tr class="row-odd"><th class="head"><p>Value</p></th>650<th class="head"><p>Codecs</p></th>651<th class="head"><p>Meaning</p></th>652</tr>653</thead>654<tbody>655<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">'surrogatepass'</span></code></p></td>656<td><p>utf-8, utf-16, utf-32,657utf-16-be, utf-16-le,658utf-32-be, utf-32-le</p></td>659<td><p>Allow encoding and decoding surrogate code660point (<code class="docutils literal notranslate"><span class="pre">U+D800</span></code> - <code class="docutils literal notranslate"><span class="pre">U+DFFF</span></code>) as normal661code point. Otherwise these codecs treat662the presence of surrogate code point in663<a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a> as an error.</p></td>664</tr>665</tbody>666</table>667<div class="versionadded">668<p><span class="versionmodified added">Added in version 3.1: </span>The <code class="docutils literal notranslate"><span class="pre">'surrogateescape'</span></code> and <code class="docutils literal notranslate"><span class="pre">'surrogatepass'</span></code> error handlers.</p>669</div>670<div class="versionchanged">671<p><span class="versionmodified changed">Changed in version 3.4: </span>The <code class="docutils literal notranslate"><span class="pre">'surrogatepass'</span></code> error handler now works with utf-16* and utf-32*672codecs.</p>673</div>674<div class="versionadded">675<p><span class="versionmodified added">Added in version 3.5: </span>The <code class="docutils literal notranslate"><span class="pre">'namereplace'</span></code> error handler.</p>676</div>677<div class="versionchanged">678<p><span class="versionmodified changed">Changed in version 3.5: </span>The <code class="docutils literal notranslate"><span class="pre">'backslashreplace'</span></code> error handler now works with decoding and679translating.</p>680</div>681<p>The set of allowed values can be extended by registering a new named error682handler:</p>683<dl class="py function">684<dt class="sig sig-object py" id="codecs.register_error">685<span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">register_error</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">name</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">error_handler</span></span></em>, <em class="sig-param"><span class="positional-only-separator o"><abbr title="Positional-only parameter separator (PEP 570)"><span class="pre">/</span></abbr></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.register_error" title="Link to this definition">¶</a></dt>686<dd><p>Register the error handling function <em>error_handler</em> under the name <em>name</em>.687The <em>error_handler</em> argument will be called during encoding and decoding688in case of an error, when <em>name</em> is specified as the errors parameter.</p>689<p>For encoding, <em>error_handler</em> will be called with a <a class="reference internal" href="exceptions.html#UnicodeEncodeError" title="UnicodeEncodeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">UnicodeEncodeError</span></code></a>690instance, which contains information about the location of the error. The691error handler must either raise this or a different exception, or return a692tuple with a replacement for the unencodable part of the input and a position693where encoding should continue. The replacement may be either <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a> or694<a class="reference internal" href="stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code></a>. If the replacement is bytes, the encoder will simply copy695them into the output buffer. If the replacement is a string, the encoder will696encode the replacement. Encoding continues on original input at the697specified position. Negative position values will be treated as being698relative to the end of the input string. If the resulting position is out of699bound an <a class="reference internal" href="exceptions.html#IndexError" title="IndexError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">IndexError</span></code></a> will be raised.</p>700<p>Decoding and translating works similarly, except <a class="reference internal" href="exceptions.html#UnicodeDecodeError" title="UnicodeDecodeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">UnicodeDecodeError</span></code></a> or701<a class="reference internal" href="exceptions.html#UnicodeTranslateError" title="UnicodeTranslateError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">UnicodeTranslateError</span></code></a> will be passed to the handler and that the702replacement from the error handler will be put into the output directly.</p>703</dd></dl>704 705<p>Previously registered error handlers (including the standard error handlers)706can be looked up by name:</p>707<dl class="py function">708<dt class="sig sig-object py" id="codecs.lookup_error">709<span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">lookup_error</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">name</span></span></em>, <em class="sig-param"><span class="positional-only-separator o"><abbr title="Positional-only parameter separator (PEP 570)"><span class="pre">/</span></abbr></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.lookup_error" title="Link to this definition">¶</a></dt>710<dd><p>Return the error handler previously registered under the name <em>name</em>.</p>711<p>Raises a <a class="reference internal" href="exceptions.html#LookupError" title="LookupError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">LookupError</span></code></a> in case the handler cannot be found.</p>712</dd></dl>713 714<p>The following standard error handlers are also made available as module level715functions:</p>716<dl class="py function">717<dt class="sig sig-object py" id="codecs.strict_errors">718<span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">strict_errors</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">exception</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.strict_errors" title="Link to this definition">¶</a></dt>719<dd><p>Implements the <code class="docutils literal notranslate"><span class="pre">'strict'</span></code> error handling.</p>720<p>Each encoding or decoding error raises a <a class="reference internal" href="exceptions.html#UnicodeError" title="UnicodeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">UnicodeError</span></code></a>.</p>721</dd></dl>722 723<dl class="py function">724<dt class="sig sig-object py" id="codecs.ignore_errors">725<span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">ignore_errors</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">exception</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.ignore_errors" title="Link to this definition">¶</a></dt>726<dd><p>Implements the <code class="docutils literal notranslate"><span class="pre">'ignore'</span></code> error handling.</p>727<p>Malformed data is ignored; encoding or decoding is continued without728further notice.</p>729</dd></dl>730 731<dl class="py function">732<dt class="sig sig-object py" id="codecs.replace_errors">733<span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">replace_errors</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">exception</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.replace_errors" title="Link to this definition">¶</a></dt>734<dd><p>Implements the <code class="docutils literal notranslate"><span class="pre">'replace'</span></code> error handling.</p>735<p>Substitutes <code class="docutils literal notranslate"><span class="pre">?</span></code> (ASCII character) for encoding errors or <code class="docutils literal notranslate"><span class="pre">�</span></code> (U+FFFD,736the official REPLACEMENT CHARACTER) for decoding errors.</p>737</dd></dl>738 739<dl class="py function">740<dt class="sig sig-object py" id="codecs.backslashreplace_errors">741<span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">backslashreplace_errors</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">exception</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.backslashreplace_errors" title="Link to this definition">¶</a></dt>742<dd><p>Implements the <code class="docutils literal notranslate"><span class="pre">'backslashreplace'</span></code> error handling.</p>743<p>Malformed data is replaced by a backslashed escape sequence.744On encoding, use the hexadecimal form of Unicode code point with formats745<code class="samp docutils literal notranslate"><span class="pre">\x</span><em><span class="pre">hh</span></em></code> <code class="samp docutils literal notranslate"><span class="pre">\u</span><em><span class="pre">xxxx</span></em></code> <code class="samp docutils literal notranslate"><span class="pre">\U</span><em><span class="pre">xxxxxxxx</span></em></code>.746On decoding, use the hexadecimal form of747byte value with format <code class="samp docutils literal notranslate"><span class="pre">\x</span><em><span class="pre">hh</span></em></code>.</p>748<div class="versionchanged">749<p><span class="versionmodified changed">Changed in version 3.5: </span>Works with decoding and translating.</p>750</div>751</dd></dl>752 753<dl class="py function">754<dt class="sig sig-object py" id="codecs.xmlcharrefreplace_errors">755<span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">xmlcharrefreplace_errors</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">exception</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.xmlcharrefreplace_errors" title="Link to this definition">¶</a></dt>756<dd><p>Implements the <code class="docutils literal notranslate"><span class="pre">'xmlcharrefreplace'</span></code> error handling (for encoding within757<a class="reference internal" href="../glossary.html#term-text-encoding"><span class="xref std std-term">text encoding</span></a> only).</p>758<p>The unencodable character is replaced by an appropriate XML/HTML numeric759character reference, which is a decimal form of Unicode code point with760format <code class="samp docutils literal notranslate"><span class="pre">&amp;#</span><em><span class="pre">num</span></em><span class="pre">;</span></code> .</p>761</dd></dl>762 763<dl class="py function">764<dt class="sig sig-object py" id="codecs.namereplace_errors">765<span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">namereplace_errors</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">exception</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.namereplace_errors" title="Link to this definition">¶</a></dt>766<dd><p>Implements the <code class="docutils literal notranslate"><span class="pre">'namereplace'</span></code> error handling (for encoding within767<a class="reference internal" href="../glossary.html#term-text-encoding"><span class="xref std std-term">text encoding</span></a> only).</p>768<p>The unencodable character is replaced by a <code class="docutils literal notranslate"><span class="pre">\N{...}</span></code> escape sequence. The769set of characters that appear in the braces is the Name property from770Unicode Character Database. For example, the German lowercase letter <code class="docutils literal notranslate"><span class="pre">'ß'</span></code>771will be converted to byte sequence <code class="docutils literal notranslate"><span class="pre">\N{LATIN</span> <span class="pre">SMALL</span> <span class="pre">LETTER</span> <span class="pre">SHARP</span> <span class="pre">S}</span></code> .</p>772<div class="versionadded">773<p><span class="versionmodified added">Added in version 3.5.</span></p>774</div>775</dd></dl>776 777</section>778<section id="stateless-encoding-and-decoding">779<span id="codec-objects"></span><h3>Stateless Encoding and Decoding<a class="headerlink" href="#stateless-encoding-and-decoding" title="Link to this heading">¶</a></h3>780<p>The base <a class="reference internal" href="#codecs.Codec" title="codecs.Codec"><code class="xref py py-class docutils literal notranslate"><span class="pre">Codec</span></code></a> class defines these methods which also define the781function interfaces of the stateless encoder and decoder:</p>782<dl class="py class">783<dt class="sig sig-object py" id="codecs.Codec">784<em class="property"><span class="k"><span class="pre">class</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">Codec</span></span><a class="headerlink" href="#codecs.Codec" title="Link to this definition">¶</a></dt>785<dd><dl class="py method">786<dt class="sig sig-object py" id="codecs.Codec.encode">787<span class="sig-name descname"><span class="pre">encode</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">input</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">errors</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">'strict'</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.Codec.encode" title="Link to this definition">¶</a></dt>788<dd><p>Encodes the object <em>input</em> and returns a tuple (output object, length consumed).789For instance, <a class="reference internal" href="../glossary.html#term-text-encoding"><span class="xref std std-term">text encoding</span></a> converts790a string object to a bytes object using a particular791character set encoding (e.g., <code class="docutils literal notranslate"><span class="pre">cp1252</span></code> or <code class="docutils literal notranslate"><span class="pre">iso-8859-1</span></code>).</p>792<p>The <em>errors</em> argument defines the error handling to apply.793It defaults to <code class="docutils literal notranslate"><span class="pre">'strict'</span></code> handling.</p>794<p>The method may not store state in the <code class="xref py py-class docutils literal notranslate"><span class="pre">Codec</span></code> instance. Use795<a class="reference internal" href="#codecs.StreamWriter" title="codecs.StreamWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamWriter</span></code></a> for codecs which have to keep state in order to make796encoding efficient.</p>797<p>The encoder must be able to handle zero length input and return an empty object798of the output object type in this situation.</p>799</dd></dl>800 801<dl class="py method">802<dt class="sig sig-object py" id="codecs.Codec.decode">803<span class="sig-name descname"><span class="pre">decode</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">input</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">errors</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">'strict'</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.Codec.decode" title="Link to this definition">¶</a></dt>804<dd><p>Decodes the object <em>input</em> and returns a tuple (output object, length805consumed). For instance, for a <a class="reference internal" href="../glossary.html#term-text-encoding"><span class="xref std std-term">text encoding</span></a>, decoding converts806a bytes object encoded using a particular807character set encoding to a string object.</p>808<p>For text encodings and bytes-to-bytes codecs,809<em>input</em> must be a bytes object or one which provides the read-only810buffer interface – for example, buffer objects and memory mapped files.</p>811<p>The <em>errors</em> argument defines the error handling to apply.812It defaults to <code class="docutils literal notranslate"><span class="pre">'strict'</span></code> handling.</p>813<p>The method may not store state in the <code class="xref py py-class docutils literal notranslate"><span class="pre">Codec</span></code> instance. Use814<a class="reference internal" href="#codecs.StreamReader" title="codecs.StreamReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReader</span></code></a> for codecs which have to keep state in order to make815decoding efficient.</p>816<p>The decoder must be able to handle zero length input and return an empty object817of the output object type in this situation.</p>818</dd></dl>819 820</dd></dl>821 822</section>823<section id="incremental-encoding-and-decoding">824<h3>Incremental Encoding and Decoding<a class="headerlink" href="#incremental-encoding-and-decoding" title="Link to this heading">¶</a></h3>825<p>The <a class="reference internal" href="#codecs.IncrementalEncoder" title="codecs.IncrementalEncoder"><code class="xref py py-class docutils literal notranslate"><span class="pre">IncrementalEncoder</span></code></a> and <a class="reference internal" href="#codecs.IncrementalDecoder" title="codecs.IncrementalDecoder"><code class="xref py py-class docutils literal notranslate"><span class="pre">IncrementalDecoder</span></code></a> classes provide826the basic interface for incremental encoding and decoding. Encoding/decoding the827input isn’t done with one call to the stateless encoder/decoder function, but828with multiple calls to the829<a class="reference internal" href="#codecs.IncrementalEncoder.encode" title="codecs.IncrementalEncoder.encode"><code class="xref py py-meth docutils literal notranslate"><span class="pre">encode()</span></code></a>/<a class="reference internal" href="#codecs.IncrementalDecoder.decode" title="codecs.IncrementalDecoder.decode"><code class="xref py py-meth docutils literal notranslate"><span class="pre">decode()</span></code></a> method of830the incremental encoder/decoder. The incremental encoder/decoder keeps track of831the encoding/decoding process during method calls.</p>832<p>The joined output of calls to the833<a class="reference internal" href="#codecs.IncrementalEncoder.encode" title="codecs.IncrementalEncoder.encode"><code class="xref py py-meth docutils literal notranslate"><span class="pre">encode()</span></code></a>/<a class="reference internal" href="#codecs.IncrementalDecoder.decode" title="codecs.IncrementalDecoder.decode"><code class="xref py py-meth docutils literal notranslate"><span class="pre">decode()</span></code></a> method is834the same as if all the single inputs were joined into one, and this input was835encoded/decoded with the stateless encoder/decoder.</p>836<section id="incrementalencoder-objects">837<span id="incremental-encoder-objects"></span><h4>IncrementalEncoder Objects<a class="headerlink" href="#incrementalencoder-objects" title="Link to this heading">¶</a></h4>838<p>The <a class="reference internal" href="#codecs.IncrementalEncoder" title="codecs.IncrementalEncoder"><code class="xref py py-class docutils literal notranslate"><span class="pre">IncrementalEncoder</span></code></a> class is used for encoding an input in multiple839steps. It defines the following methods which every incremental encoder must840define in order to be compatible with the Python codec registry.</p>841<dl class="py class">842<dt class="sig sig-object py" id="codecs.IncrementalEncoder">843<em class="property"><span class="k"><span class="pre">class</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">IncrementalEncoder</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">errors</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">'strict'</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.IncrementalEncoder" title="Link to this definition">¶</a></dt>844<dd><p>Constructor for an <code class="xref py py-class docutils literal notranslate"><span class="pre">IncrementalEncoder</span></code> instance.</p>845<p>All incremental encoders must provide this constructor interface. They are free846to add additional keyword arguments, but only the ones defined here are used by847the Python codec registry.</p>848<p>The <code class="xref py py-class docutils literal notranslate"><span class="pre">IncrementalEncoder</span></code> may implement different error handling schemes849by providing the <em>errors</em> keyword argument. See <a class="reference internal" href="#error-handlers"><span class="std std-ref">Error Handlers</span></a> for850possible values.</p>851<p>The <em>errors</em> argument will be assigned to an attribute of the same name.852Assigning to this attribute makes it possible to switch between different error853handling strategies during the lifetime of the <code class="xref py py-class docutils literal notranslate"><span class="pre">IncrementalEncoder</span></code>854object.</p>855<dl class="py method">856<dt class="sig sig-object py" id="codecs.IncrementalEncoder.encode">857<span class="sig-name descname"><span class="pre">encode</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">object</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">final</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">False</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.IncrementalEncoder.encode" title="Link to this definition">¶</a></dt>858<dd><p>Encodes <em>object</em> (taking the current state of the encoder into account)859and returns the resulting encoded object. If this is the last call to860<code class="xref py py-meth docutils literal notranslate"><span class="pre">encode()</span></code> <em>final</em> must be true (the default is false).</p>861</dd></dl>862 863<dl class="py method">864<dt class="sig sig-object py" id="codecs.IncrementalEncoder.reset">865<span class="sig-name descname"><span class="pre">reset</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#codecs.IncrementalEncoder.reset" title="Link to this definition">¶</a></dt>866<dd><p>Reset the encoder to the initial state. The output is discarded: call867<code class="docutils literal notranslate"><span class="pre">.encode(object,</span> <span class="pre">final=True)</span></code>, passing an empty byte or text string868if necessary, to reset the encoder and to get the output.</p>869</dd></dl>870 871<dl class="py method">872<dt class="sig sig-object py" id="codecs.IncrementalEncoder.getstate">873<span class="sig-name descname"><span class="pre">getstate</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#codecs.IncrementalEncoder.getstate" title="Link to this definition">¶</a></dt>874<dd><p>Return the current state of the encoder which must be an integer. The875implementation should make sure that <code class="docutils literal notranslate"><span class="pre">0</span></code> is the most common876state. (States that are more complicated than integers can be converted877into an integer by marshaling/pickling the state and encoding the bytes878of the resulting string into an integer.)</p>879</dd></dl>880 881<dl class="py method">882<dt class="sig sig-object py" id="codecs.IncrementalEncoder.setstate">883<span class="sig-name descname"><span class="pre">setstate</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">state</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.IncrementalEncoder.setstate" title="Link to this definition">¶</a></dt>884<dd><p>Set the state of the encoder to <em>state</em>. <em>state</em> must be an encoder state885returned by <a class="reference internal" href="#codecs.IncrementalEncoder.getstate" title="codecs.IncrementalEncoder.getstate"><code class="xref py py-meth docutils literal notranslate"><span class="pre">getstate()</span></code></a>.</p>886</dd></dl>887 888</dd></dl>889 890</section>891<section id="incrementaldecoder-objects">892<span id="incremental-decoder-objects"></span><h4>IncrementalDecoder Objects<a class="headerlink" href="#incrementaldecoder-objects" title="Link to this heading">¶</a></h4>893<p>The <a class="reference internal" href="#codecs.IncrementalDecoder" title="codecs.IncrementalDecoder"><code class="xref py py-class docutils literal notranslate"><span class="pre">IncrementalDecoder</span></code></a> class is used for decoding an input in multiple894steps. It defines the following methods which every incremental decoder must895define in order to be compatible with the Python codec registry.</p>896<dl class="py class">897<dt class="sig sig-object py" id="codecs.IncrementalDecoder">898<em class="property"><span class="k"><span class="pre">class</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">IncrementalDecoder</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">errors</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">'strict'</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.IncrementalDecoder" title="Link to this definition">¶</a></dt>899<dd><p>Constructor for an <code class="xref py py-class docutils literal notranslate"><span class="pre">IncrementalDecoder</span></code> instance.</p>900<p>All incremental decoders must provide this constructor interface. They are free901to add additional keyword arguments, but only the ones defined here are used by902the Python codec registry.</p>903<p>The <code class="xref py py-class docutils literal notranslate"><span class="pre">IncrementalDecoder</span></code> may implement different error handling schemes904by providing the <em>errors</em> keyword argument. See <a class="reference internal" href="#error-handlers"><span class="std std-ref">Error Handlers</span></a> for905possible values.</p>906<p>The <em>errors</em> argument will be assigned to an attribute of the same name.907Assigning to this attribute makes it possible to switch between different error908handling strategies during the lifetime of the <code class="xref py py-class docutils literal notranslate"><span class="pre">IncrementalDecoder</span></code>909object.</p>910<dl class="py method">911<dt class="sig sig-object py" id="codecs.IncrementalDecoder.decode">912<span class="sig-name descname"><span class="pre">decode</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">object</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">final</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">False</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.IncrementalDecoder.decode" title="Link to this definition">¶</a></dt>913<dd><p>Decodes <em>object</em> (taking the current state of the decoder into account)914and returns the resulting decoded object. If this is the last call to915<code class="xref py py-meth docutils literal notranslate"><span class="pre">decode()</span></code> <em>final</em> must be true (the default is false). If <em>final</em> is916true the decoder must decode the input completely and must flush all917buffers. If this isn’t possible (e.g. because of incomplete byte sequences918at the end of the input) it must initiate error handling just like in the919stateless case (which might raise an exception).</p>920</dd></dl>921 922<dl class="py method">923<dt class="sig sig-object py" id="codecs.IncrementalDecoder.reset">924<span class="sig-name descname"><span class="pre">reset</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#codecs.IncrementalDecoder.reset" title="Link to this definition">¶</a></dt>925<dd><p>Reset the decoder to the initial state.</p>926</dd></dl>927 928<dl class="py method">929<dt class="sig sig-object py" id="codecs.IncrementalDecoder.getstate">930<span class="sig-name descname"><span class="pre">getstate</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#codecs.IncrementalDecoder.getstate" title="Link to this definition">¶</a></dt>931<dd><p>Return the current state of the decoder. This must be a tuple with two932items, the first must be the buffer containing the still undecoded933input. The second must be an integer and can be additional state934info. (The implementation should make sure that <code class="docutils literal notranslate"><span class="pre">0</span></code> is the most common935additional state info.) If this additional state info is <code class="docutils literal notranslate"><span class="pre">0</span></code> it must be936possible to set the decoder to the state which has no input buffered and937<code class="docutils literal notranslate"><span class="pre">0</span></code> as the additional state info, so that feeding the previously938buffered input to the decoder returns it to the previous state without939producing any output. (Additional state info that is more complicated than940integers can be converted into an integer by marshaling/pickling the info941and encoding the bytes of the resulting string into an integer.)</p>942</dd></dl>943 944<dl class="py method">945<dt class="sig sig-object py" id="codecs.IncrementalDecoder.setstate">946<span class="sig-name descname"><span class="pre">setstate</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">state</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.IncrementalDecoder.setstate" title="Link to this definition">¶</a></dt>947<dd><p>Set the state of the decoder to <em>state</em>. <em>state</em> must be a decoder state948returned by <a class="reference internal" href="#codecs.IncrementalDecoder.getstate" title="codecs.IncrementalDecoder.getstate"><code class="xref py py-meth docutils literal notranslate"><span class="pre">getstate()</span></code></a>.</p>949</dd></dl>950 951</dd></dl>952 953</section>954</section>955<section id="stream-encoding-and-decoding">956<h3>Stream Encoding and Decoding<a class="headerlink" href="#stream-encoding-and-decoding" title="Link to this heading">¶</a></h3>957<p>The <a class="reference internal" href="#codecs.StreamWriter" title="codecs.StreamWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamWriter</span></code></a> and <a class="reference internal" href="#codecs.StreamReader" title="codecs.StreamReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReader</span></code></a> classes provide generic958working interfaces which can be used to implement new encoding submodules very959easily. See <code class="xref py py-mod docutils literal notranslate"><span class="pre">encodings.utf_8</span></code> for an example of how this is done.</p>960<section id="streamwriter-objects">961<span id="stream-writer-objects"></span><h4>StreamWriter Objects<a class="headerlink" href="#streamwriter-objects" title="Link to this heading">¶</a></h4>962<p>The <a class="reference internal" href="#codecs.StreamWriter" title="codecs.StreamWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamWriter</span></code></a> class is a subclass of <a class="reference internal" href="#codecs.Codec" title="codecs.Codec"><code class="xref py py-class docutils literal notranslate"><span class="pre">Codec</span></code></a> and defines the963following methods which every stream writer must define in order to be964compatible with the Python codec registry.</p>965<dl class="py class">966<dt class="sig sig-object py" id="codecs.StreamWriter">967<em class="property"><span class="k"><span class="pre">class</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">StreamWriter</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">stream</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">errors</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">'strict'</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.StreamWriter" title="Link to this definition">¶</a></dt>968<dd><p>Constructor for a <code class="xref py py-class docutils literal notranslate"><span class="pre">StreamWriter</span></code> instance.</p>969<p>All stream writers must provide this constructor interface. They are free to add970additional keyword arguments, but only the ones defined here are used by the971Python codec registry.</p>972<p>The <em>stream</em> argument must be a file-like object open for writing973text or binary data, as appropriate for the specific codec.</p>974<p>The <code class="xref py py-class docutils literal notranslate"><span class="pre">StreamWriter</span></code> may implement different error handling schemes by975providing the <em>errors</em> keyword argument. See <a class="reference internal" href="#error-handlers"><span class="std std-ref">Error Handlers</span></a> for976the standard error handlers the underlying stream codec may support.</p>977<p>The <em>errors</em> argument will be assigned to an attribute of the same name.978Assigning to this attribute makes it possible to switch between different error979handling strategies during the lifetime of the <code class="xref py py-class docutils literal notranslate"><span class="pre">StreamWriter</span></code> object.</p>980<dl class="py method">981<dt class="sig sig-object py" id="codecs.StreamWriter.write">982<span class="sig-name descname"><span class="pre">write</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">object</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.StreamWriter.write" title="Link to this definition">¶</a></dt>983<dd><p>Writes the object’s contents encoded to the stream.</p>984</dd></dl>985 986<dl class="py method">987<dt class="sig sig-object py" id="codecs.StreamWriter.writelines">988<span class="sig-name descname"><span class="pre">writelines</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">list</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.StreamWriter.writelines" title="Link to this definition">¶</a></dt>989<dd><p>Writes the concatenated iterable of strings to the stream (possibly by reusing990the <a class="reference internal" href="#codecs.StreamWriter.write" title="codecs.StreamWriter.write"><code class="xref py py-meth docutils literal notranslate"><span class="pre">write()</span></code></a> method). Infinite or991very large iterables are not supported. The standard bytes-to-bytes codecs992do not support this method.</p>993</dd></dl>994 995<dl class="py method">996<dt class="sig sig-object py" id="codecs.StreamWriter.reset">997<span class="sig-name descname"><span class="pre">reset</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#codecs.StreamWriter.reset" title="Link to this definition">¶</a></dt>998<dd><p>Resets the codec buffers used for keeping internal state.</p>999<p>Calling this method should ensure that the data on the output is put into1000a clean state that allows appending of new fresh data without having to1001rescan the whole stream to recover state.</p>1002</dd></dl>1003 1004</dd></dl>1005 1006<p>In addition to the above methods, the <a class="reference internal" href="#codecs.StreamWriter" title="codecs.StreamWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamWriter</span></code></a> must also inherit1007all other methods and attributes from the underlying stream.</p>1008</section>1009<section id="streamreader-objects">1010<span id="stream-reader-objects"></span><h4>StreamReader Objects<a class="headerlink" href="#streamreader-objects" title="Link to this heading">¶</a></h4>1011<p>The <a class="reference internal" href="#codecs.StreamReader" title="codecs.StreamReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReader</span></code></a> class is a subclass of <a class="reference internal" href="#codecs.Codec" title="codecs.Codec"><code class="xref py py-class docutils literal notranslate"><span class="pre">Codec</span></code></a> and defines the1012following methods which every stream reader must define in order to be1013compatible with the Python codec registry.</p>1014<dl class="py class">1015<dt class="sig sig-object py" id="codecs.StreamReader">1016<em class="property"><span class="k"><span class="pre">class</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">StreamReader</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">stream</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">errors</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">'strict'</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.StreamReader" title="Link to this definition">¶</a></dt>1017<dd><p>Constructor for a <code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReader</span></code> instance.</p>1018<p>All stream readers must provide this constructor interface. They are free to add1019additional keyword arguments, but only the ones defined here are used by the1020Python codec registry.</p>1021<p>The <em>stream</em> argument must be a file-like object open for reading1022text or binary data, as appropriate for the specific codec.</p>1023<p>The <code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReader</span></code> may implement different error handling schemes by1024providing the <em>errors</em> keyword argument. See <a class="reference internal" href="#error-handlers"><span class="std std-ref">Error Handlers</span></a> for1025the standard error handlers the underlying stream codec may support.</p>1026<p>The <em>errors</em> argument will be assigned to an attribute of the same name.1027Assigning to this attribute makes it possible to switch between different error1028handling strategies during the lifetime of the <code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReader</span></code> object.</p>1029<p>The set of allowed values for the <em>errors</em> argument can be extended with1030<a class="reference internal" href="#codecs.register_error" title="codecs.register_error"><code class="xref py py-func docutils literal notranslate"><span class="pre">register_error()</span></code></a>.</p>1031<dl class="py method">1032<dt class="sig sig-object py" id="codecs.StreamReader.read">1033<span class="sig-name descname"><span class="pre">read</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">size</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">-1</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">chars</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">-1</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">firstline</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">False</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.StreamReader.read" title="Link to this definition">¶</a></dt>1034<dd><p>Decodes data from the stream and returns the resulting object.</p>1035<p>The <em>chars</em> argument indicates the number of decoded1036code points or bytes to return. The <a class="reference internal" href="#codecs.StreamReader.read" title="codecs.StreamReader.read"><code class="xref py py-func docutils literal notranslate"><span class="pre">read()</span></code></a> method will1037never return more data than requested, but it might return less,1038if there is not enough available.</p>1039<p>The <em>size</em> argument indicates the approximate maximum1040number of encoded bytes or code points to read1041for decoding. The decoder can modify this setting as1042appropriate. The default value -1 indicates to read and decode as much as1043possible. This parameter is intended to1044prevent having to decode huge files in one step.</p>1045<p>The <em>firstline</em> flag indicates that1046it would be sufficient to only return the first1047line, if there are decoding errors on later lines.</p>1048<p>The method should use a greedy read strategy meaning that it should read1049as much data as is allowed within the definition of the encoding and the1050given size, e.g.  if optional encoding endings or state markers are1051available on the stream, these should be read too.</p>1052</dd></dl>1053 1054<dl class="py method">1055<dt class="sig sig-object py" id="codecs.StreamReader.readline">1056<span class="sig-name descname"><span class="pre">readline</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">size</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">keepends</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">True</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.StreamReader.readline" title="Link to this definition">¶</a></dt>1057<dd><p>Read one line from the input stream and return the decoded data.</p>1058<p><em>size</em>, if given, is passed as size argument to the stream’s1059<a class="reference internal" href="#codecs.StreamReader.read" title="codecs.StreamReader.read"><code class="xref py py-meth docutils literal notranslate"><span class="pre">read()</span></code></a> method.</p>1060<p>If <em>keepends</em> is false line-endings will be stripped from the lines1061returned.</p>1062</dd></dl>1063 1064<dl class="py method">1065<dt class="sig sig-object py" id="codecs.StreamReader.readlines">1066<span class="sig-name descname"><span class="pre">readlines</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">sizehint</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">keepends</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">True</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.StreamReader.readlines" title="Link to this definition">¶</a></dt>1067<dd><p>Read all lines available on the input stream and return them as a list of1068lines.</p>1069<p>Line-endings are implemented using the codec’s <a class="reference internal" href="#codecs.decode" title="codecs.decode"><code class="xref py py-meth docutils literal notranslate"><span class="pre">decode()</span></code></a> method and1070are included in the list entries if <em>keepends</em> is true.</p>1071<p><em>sizehint</em>, if given, is passed as the <em>size</em> argument to the stream’s1072<a class="reference internal" href="#codecs.StreamReader.read" title="codecs.StreamReader.read"><code class="xref py py-meth docutils literal notranslate"><span class="pre">read()</span></code></a> method.</p>1073</dd></dl>1074 1075<dl class="py method">1076<dt class="sig sig-object py" id="codecs.StreamReader.reset">1077<span class="sig-name descname"><span class="pre">reset</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#codecs.StreamReader.reset" title="Link to this definition">¶</a></dt>1078<dd><p>Resets the codec buffers used for keeping internal state.</p>1079<p>Note that no stream repositioning should take place. This method is1080primarily intended to be able to recover from decoding errors.</p>1081</dd></dl>1082 1083</dd></dl>1084 1085<p>In addition to the above methods, the <a class="reference internal" href="#codecs.StreamReader" title="codecs.StreamReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReader</span></code></a> must also inherit1086all other methods and attributes from the underlying stream.</p>1087</section>1088<section id="streamreaderwriter-objects">1089<span id="stream-reader-writer"></span><h4>StreamReaderWriter Objects<a class="headerlink" href="#streamreaderwriter-objects" title="Link to this heading">¶</a></h4>1090<p>The <a class="reference internal" href="#codecs.StreamReaderWriter" title="codecs.StreamReaderWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReaderWriter</span></code></a> is a convenience class that allows wrapping1091streams which work in both read and write modes.</p>1092<p>The design is such that one can use the factory functions returned by the1093<a class="reference internal" href="#codecs.lookup" title="codecs.lookup"><code class="xref py py-func docutils literal notranslate"><span class="pre">lookup()</span></code></a> function to construct the instance.</p>1094<dl class="py class">1095<dt class="sig sig-object py" id="codecs.StreamReaderWriter">1096<em class="property"><span class="k"><span class="pre">class</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">StreamReaderWriter</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">stream</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">Reader</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">Writer</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">errors</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">'strict'</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.StreamReaderWriter" title="Link to this definition">¶</a></dt>1097<dd><p>Creates a <code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReaderWriter</span></code> instance. <em>stream</em> must be a file-like1098object. <em>Reader</em> and <em>Writer</em> must be factory functions or classes providing the1099<a class="reference internal" href="#codecs.StreamReader" title="codecs.StreamReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReader</span></code></a> and <a class="reference internal" href="#codecs.StreamWriter" title="codecs.StreamWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamWriter</span></code></a> interface resp. Error handling1100is done in the same way as defined for the stream readers and writers.</p>1101</dd></dl>1102 1103<p><a class="reference internal" href="#codecs.StreamReaderWriter" title="codecs.StreamReaderWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReaderWriter</span></code></a> instances define the combined interfaces of1104<a class="reference internal" href="#codecs.StreamReader" title="codecs.StreamReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReader</span></code></a> and <a class="reference internal" href="#codecs.StreamWriter" title="codecs.StreamWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamWriter</span></code></a> classes. They inherit all other1105methods and attributes from the underlying stream.</p>1106</section>1107<section id="streamrecoder-objects">1108<span id="stream-recoder-objects"></span><h4>StreamRecoder Objects<a class="headerlink" href="#streamrecoder-objects" title="Link to this heading">¶</a></h4>1109<p>The <a class="reference internal" href="#codecs.StreamRecoder" title="codecs.StreamRecoder"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamRecoder</span></code></a> translates data from one encoding to another,1110which is sometimes useful when dealing with different encoding environments.</p>1111<p>The design is such that one can use the factory functions returned by the1112<a class="reference internal" href="#codecs.lookup" title="codecs.lookup"><code class="xref py py-func docutils literal notranslate"><span class="pre">lookup()</span></code></a> function to construct the instance.</p>1113<dl class="py class">1114<dt class="sig sig-object py" id="codecs.StreamRecoder">1115<em class="property"><span class="k"><span class="pre">class</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">codecs.</span></span><span class="sig-name descname"><span class="pre">StreamRecoder</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">stream</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">encode</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">decode</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">Reader</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">Writer</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">errors</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">'strict'</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.StreamRecoder" title="Link to this definition">¶</a></dt>1116<dd><p>Creates a <code class="xref py py-class docutils literal notranslate"><span class="pre">StreamRecoder</span></code> instance which implements a two-way conversion:1117<em>encode</em> and <em>decode</em> work on the frontend — the data visible to1118code calling <a class="reference internal" href="#codecs.StreamReader.read" title="codecs.StreamReader.read"><code class="xref py py-meth docutils literal notranslate"><span class="pre">read()</span></code></a> and <a class="reference internal" href="#codecs.StreamWriter.write" title="codecs.StreamWriter.write"><code class="xref py py-meth docutils literal notranslate"><span class="pre">write()</span></code></a>,1119while <em>Reader</em> and <em>Writer</em>1120work on the backend — the data in <em>stream</em>.</p>1121<p>You can use these objects to do transparent transcodings, e.g., from Latin-11122to UTF-8 and back.</p>1123<p>The <em>stream</em> argument must be a file-like object.</p>1124<p>The <em>encode</em> and <em>decode</em> arguments must1125adhere to the <a class="reference internal" href="#codecs.Codec" title="codecs.Codec"><code class="xref py py-class docutils literal notranslate"><span class="pre">Codec</span></code></a> interface. <em>Reader</em> and1126<em>Writer</em> must be factory functions or classes providing objects of the1127<a class="reference internal" href="#codecs.StreamReader" title="codecs.StreamReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReader</span></code></a> and <a class="reference internal" href="#codecs.StreamWriter" title="codecs.StreamWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamWriter</span></code></a> interface respectively.</p>1128<p>Error handling is done in the same way as defined for the stream readers and1129writers.</p>1130</dd></dl>1131 1132<p><a class="reference internal" href="#codecs.StreamRecoder" title="codecs.StreamRecoder"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamRecoder</span></code></a> instances define the combined interfaces of1133<a class="reference internal" href="#codecs.StreamReader" title="codecs.StreamReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReader</span></code></a> and <a class="reference internal" href="#codecs.StreamWriter" title="codecs.StreamWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamWriter</span></code></a> classes. They inherit all other1134methods and attributes from the underlying stream.</p>1135</section>1136</section>1137</section>1138<section id="encodings-and-unicode">1139<span id="encodings-overview"></span><h2>Encodings and Unicode<a class="headerlink" href="#encodings-and-unicode" title="Link to this heading">¶</a></h2>1140<p>Strings are stored internally as sequences of code points in1141range <code class="docutils literal notranslate"><span class="pre">U+0000</span></code>–<code class="docutils literal notranslate"><span class="pre">U+10FFFF</span></code>. (See <span class="target" id="index-5"></span><a class="pep reference external" href="https://peps.python.org/pep-0393/"><strong>PEP 393</strong></a> for1142more details about the implementation.)1143Once a string object is used outside of CPU and memory, endianness1144and how these arrays are stored as bytes become an issue. As with other1145codecs, serialising a string into a sequence of bytes is known as <em>encoding</em>,1146and recreating the string from the sequence of bytes is known as <em>decoding</em>.1147There are a variety of different text serialisation codecs, which are1148collectivity referred to as <a class="reference internal" href="../glossary.html#term-text-encoding"><span class="xref std std-term">text encodings</span></a>.</p>1149<p>The simplest text encoding (called <code class="docutils literal notranslate"><span class="pre">'latin-1'</span></code> or <code class="docutils literal notranslate"><span class="pre">'iso-8859-1'</span></code>) maps1150the code points 0–255 to the bytes <code class="docutils literal notranslate"><span class="pre">0x0</span></code>–<code class="docutils literal notranslate"><span class="pre">0xff</span></code>, which means that a string1151object that contains code points above <code class="docutils literal notranslate"><span class="pre">U+00FF</span></code> can’t be encoded with this1152codec. Doing so will raise a <a class="reference internal" href="exceptions.html#UnicodeEncodeError" title="UnicodeEncodeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">UnicodeEncodeError</span></code></a> that looks1153like the following (although the details of the error message may differ):1154<code class="docutils literal notranslate"><span class="pre">UnicodeEncodeError:</span> <span class="pre">'latin-1'</span> <span class="pre">codec</span> <span class="pre">can't</span> <span class="pre">encode</span> <span class="pre">character</span> <span class="pre">'\u1234'</span> <span class="pre">in</span>1155<span class="pre">position</span> <span class="pre">3:</span> <span class="pre">ordinal</span> <span class="pre">not</span> <span class="pre">in</span> <span class="pre">range(256)</span></code>.</p>1156<p>There’s another group of encodings (the so called charmap encodings) that choose1157a different subset of all Unicode code points and how these code points are1158mapped to the bytes <code class="docutils literal notranslate"><span class="pre">0x0</span></code>–<code class="docutils literal notranslate"><span class="pre">0xff</span></code>. To see how this is done simply open1159e.g. <code class="file docutils literal notranslate"><span class="pre">encodings/cp1252.py</span></code> (which is an encoding that is used primarily on1160Windows). There’s a string constant with 256 characters that shows you which1161character is mapped to which byte value.</p>1162<p>All of these encodings can only encode 256 of the 1114112 code points1163defined in Unicode. A simple and straightforward way that can store each Unicode1164code point, is to store each code point as four consecutive bytes. There are two1165possibilities: store the bytes in big endian or in little endian order. These1166two encodings are called <code class="docutils literal notranslate"><span class="pre">UTF-32-BE</span></code> and <code class="docutils literal notranslate"><span class="pre">UTF-32-LE</span></code> respectively. Their1167disadvantage is that if, for example, you use <code class="docutils literal notranslate"><span class="pre">UTF-32-BE</span></code> on a little endian1168machine you will always have to swap bytes on encoding and decoding.1169Python’s <code class="docutils literal notranslate"><span class="pre">UTF-16</span></code> and <code class="docutils literal notranslate"><span class="pre">UTF-32</span></code> codecs avoid this problem by using the1170platform’s native byte order when no BOM is present.1171Python follows prevailing platform1172practice, so native-endian data round-trips without redundant byte swapping,1173even though the Unicode Standard defaults to big-endian when the byte order is1174unspecified. When these bytes are read by a CPU with a different endianness,1175the bytes have to be swapped. To be able to detect the endianness of a1176<code class="docutils literal notranslate"><span class="pre">UTF-16</span></code> or <code class="docutils literal notranslate"><span class="pre">UTF-32</span></code> byte sequence, a BOM (“Byte Order Mark”) is used.1177This is the Unicode character <code class="docutils literal notranslate"><span class="pre">U+FEFF</span></code>. This character can be prepended to every1178<code class="docutils literal notranslate"><span class="pre">UTF-16</span></code> or <code class="docutils literal notranslate"><span class="pre">UTF-32</span></code> byte sequence. The byte swapped version of this character1179(<code class="docutils literal notranslate"><span class="pre">0xFFFE</span></code>) is an illegal character that may not appear in a Unicode text.1180When the first character of a <code class="docutils literal notranslate"><span class="pre">UTF-16</span></code> or <code class="docutils literal notranslate"><span class="pre">UTF-32</span></code> byte sequence is1181<code class="docutils literal notranslate"><span class="pre">U+FFFE</span></code>, the bytes have to be swapped on decoding.</p>1182<p>Unfortunately the character <code class="docutils literal notranslate"><span class="pre">U+FEFF</span></code> had a second purpose as1183a <code class="docutils literal notranslate"><span class="pre">ZERO</span> <span class="pre">WIDTH</span> <span class="pre">NO-BREAK</span> <span class="pre">SPACE</span></code>: a character that has no width and doesn’t allow1184a word to be split. It can e.g. be used to give hints to a ligature algorithm.1185With Unicode 4.0 using <code class="docutils literal notranslate"><span class="pre">U+FEFF</span></code> as a <code class="docutils literal notranslate"><span class="pre">ZERO</span> <span class="pre">WIDTH</span> <span class="pre">NO-BREAK</span> <span class="pre">SPACE</span></code> has been1186deprecated (with <code class="docutils literal notranslate"><span class="pre">U+2060</span></code> (<code class="docutils literal notranslate"><span class="pre">WORD</span> <span class="pre">JOINER</span></code>) assuming this role). Nevertheless1187Unicode software still must be able to handle <code class="docutils literal notranslate"><span class="pre">U+FEFF</span></code> in both roles: as a BOM1188it’s a device to determine the storage layout of the encoded bytes, and vanishes1189once the byte sequence has been decoded into a string; as a <code class="docutils literal notranslate"><span class="pre">ZERO</span> <span class="pre">WIDTH</span>1190<span class="pre">NO-BREAK</span> <span class="pre">SPACE</span></code> it’s a normal character that will be decoded like any other.</p>1191<p>There’s another encoding that is able to encode the full range of Unicode1192characters: UTF-8. UTF-8 is an 8-bit encoding, which means there are no issues1193with byte order in UTF-8. Each byte in a UTF-8 byte sequence consists of two1194parts: marker bits (the most significant bits) and payload bits. The marker bits1195are a sequence of zero to four <code class="docutils literal notranslate"><span class="pre">1</span></code> bits followed by a <code class="docutils literal notranslate"><span class="pre">0</span></code> bit. Unicode characters are1196encoded like this (with x being payload bits, which when concatenated give the1197Unicode character):</p>1198<table class="docutils align-default">1199<thead>1200<tr class="row-odd"><th class="head"><p>Range</p></th>

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