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 <div class="bodywrapper">217          <div class="body" role="main">218            219  <section id="module-string.templatelib">220<span id="string-templatelib-support-for-template-string-literals"></span><h1><code class="xref py py-mod docutils literal notranslate"><span class="pre">string.templatelib</span></code> — Support for template string literals<a class="headerlink" href="#module-string.templatelib" title="Link to this heading">¶</a></h1>221<p><strong>Source code:</strong> <a class="extlink-source reference external" href="https://github.com/python/cpython/tree/main/Lib/string/templatelib.py">Lib/string/templatelib.py</a></p>222<hr class="docutils" />223<div class="admonition seealso">224<p class="admonition-title">See also</p>225<ul class="simple">226<li><p><a class="reference internal" href="../reference/lexical_analysis.html#f-strings"><span class="std std-ref">Format strings</span></a></p></li>227<li><p><a class="reference internal" href="../reference/lexical_analysis.html#t-strings"><span class="std std-ref">Template string literal (t-string) syntax</span></a></p></li>228<li><p><span class="target" id="index-0"></span><a class="pep reference external" href="https://peps.python.org/pep-0750/"><strong>PEP 750</strong></a></p></li>229</ul>230</div>231<section id="template-strings">232<span id="id1"></span><h2>Template strings<a class="headerlink" href="#template-strings" title="Link to this heading">¶</a></h2>233<div class="versionadded">234<p><span class="versionmodified added">Added in version 3.14.</span></p>235</div>236<p>Template strings are a mechanism for custom string processing.237They have the full flexibility of Python’s <a class="reference internal" href="../reference/lexical_analysis.html#f-strings"><span class="std std-ref">f-strings</span></a>,238but return a <a class="reference internal" href="#string.templatelib.Template" title="string.templatelib.Template"><code class="xref py py-class docutils literal notranslate"><span class="pre">Template</span></code></a> instance that gives access239to the static and interpolated (in curly brackets) parts of a string240<em>before</em> they are combined.</p>241<p>To write a t-string, use a <code class="docutils literal notranslate"><span class="pre">'t'</span></code> prefix instead of an <code class="docutils literal notranslate"><span class="pre">'f'</span></code>, like so:</p>242<div class="highlight-pycon notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">pi</span> <span class="o">=</span> <span class="mf">3.14</span>243<span class="gp">&gt;&gt;&gt; </span><span class="n">t</span><span class="s1">&#39;t-strings are new in Python </span><span class="si">{pi!s}</span><span class="s1">!&#39;</span>244<span class="go">Template(</span>245<span class="go">   strings=(&#39;t-strings are new in Python &#39;, &#39;!&#39;),</span>246<span class="go">   interpolations=(Interpolation(3.14, &#39;pi&#39;, &#39;s&#39;, &#39;&#39;),)</span>247<span class="go">)</span>248</pre></div>249</div>250</section>251<section id="types">252<h2>Types<a class="headerlink" href="#types" title="Link to this heading">¶</a></h2>253<dl class="py class">254<dt class="sig sig-object py" id="string.templatelib.Template">255<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">string.templatelib.</span></span><span class="sig-name descname"><span class="pre">Template</span></span><a class="headerlink" href="#string.templatelib.Template" title="Link to this definition">¶</a></dt>256<dd><p>The <code class="xref py py-class docutils literal notranslate"><span class="pre">Template</span></code> class describes the contents of a template string.257It is immutable, meaning that attributes of a template cannot be reassigned.</p>258<p>The most common way to create a <code class="xref py py-class docutils literal notranslate"><span class="pre">Template</span></code> instance is to use the259<a class="reference internal" href="../reference/lexical_analysis.html#t-strings"><span class="std std-ref">template string literal syntax</span></a>.260This syntax is identical to that of <a class="reference internal" href="../reference/lexical_analysis.html#f-strings"><span class="std std-ref">f-strings</span></a>,261except that it uses a <code class="docutils literal notranslate"><span class="pre">t</span></code> prefix in place of an <code class="docutils literal notranslate"><span class="pre">f</span></code>:</p>262<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">cheese</span> <span class="o">=</span> <span class="s1">&#39;Red Leicester&#39;</span>263<span class="gp">&gt;&gt;&gt; </span><span class="n">template</span> <span class="o">=</span> <span class="n">t</span><span class="s2">&quot;We&#39;re fresh out of </span><span class="si">{cheese}</span><span class="s2">, sir.&quot;</span>264<span class="gp">&gt;&gt;&gt; </span><span class="nb">type</span><span class="p">(</span><span class="n">template</span><span class="p">)</span>265<span class="go">&lt;class &#39;string.templatelib.Template&#39;&gt;</span>266</pre></div>267</div>268<p>Templates are stored as sequences of literal <a class="reference internal" href="#string.templatelib.Template.strings" title="string.templatelib.Template.strings"><code class="xref py py-attr docutils literal notranslate"><span class="pre">strings</span></code></a>269and dynamic <a class="reference internal" href="#string.templatelib.Template.interpolations" title="string.templatelib.Template.interpolations"><code class="xref py py-attr docutils literal notranslate"><span class="pre">interpolations</span></code></a>.270A <a class="reference internal" href="#string.templatelib.Template.values" title="string.templatelib.Template.values"><code class="xref py py-attr docutils literal notranslate"><span class="pre">values</span></code></a> attribute holds the values of the interpolations:</p>271<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">cheese</span> <span class="o">=</span> <span class="s1">&#39;Camembert&#39;</span>272<span class="gp">&gt;&gt;&gt; </span><span class="n">template</span> <span class="o">=</span> <span class="n">t</span><span class="s1">&#39;Ah! We do have </span><span class="si">{cheese}</span><span class="s1">.&#39;</span>273<span class="gp">&gt;&gt;&gt; </span><span class="n">template</span><span class="o">.</span><span class="n">strings</span>274<span class="go">(&#39;Ah! We do have &#39;, &#39;.&#39;)</span>275<span class="gp">&gt;&gt;&gt; </span><span class="n">template</span><span class="o">.</span><span class="n">interpolations</span>276<span class="go">(Interpolation(&#39;Camembert&#39;, ...),)</span>277<span class="gp">&gt;&gt;&gt; </span><span class="n">template</span><span class="o">.</span><span class="n">values</span>278<span class="go">(&#39;Camembert&#39;,)</span>279</pre></div>280</div>281<p>The <code class="xref py py-attr docutils literal notranslate"><span class="pre">strings</span></code> tuple has one more element than <code class="xref py py-attr docutils literal notranslate"><span class="pre">interpolations</span></code>282and <code class="xref py py-attr docutils literal notranslate"><span class="pre">values</span></code>; the interpolations “belong” between the strings.283This may be easier to understand when tuples are aligned</p>284<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="n">template</span><span class="o">.</span><span class="n">strings</span><span class="p">:</span>  <span class="p">(</span><span class="s1">&#39;Ah! We do have &#39;</span><span class="p">,</span>              <span class="s1">&#39;.&#39;</span><span class="p">)</span>285<span class="n">template</span><span class="o">.</span><span class="n">values</span><span class="p">:</span>   <span class="p">(</span>                   <span class="s1">&#39;Camembert&#39;</span><span class="p">,</span>    <span class="p">)</span>286</pre></div>287</div>288<p class="rubric">Attributes</p>289<dl class="py attribute">290<dt class="sig sig-object py" id="string.templatelib.Template.strings">291<span class="sig-name descname"><span class="pre">strings</span></span><em class="property"><span class="p"><span class="pre">:</span></span><span class="w"> </span><a class="reference internal" href="stdtypes.html#tuple" title="tuple"><span class="pre">tuple</span></a><span class="p"><span class="pre">[</span></span><a class="reference internal" href="stdtypes.html#str" title="str"><span class="pre">str</span></a><span class="p"><span class="pre">,</span></span><span class="w"> </span><span class="p"><span class="pre">...</span></span><span class="p"><span class="pre">]</span></span></em><a class="headerlink" href="#string.templatelib.Template.strings" title="Link to this definition">¶</a></dt>292<dd><p>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> of the static strings in the template.</p>293<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">cheese</span> <span class="o">=</span> <span class="s1">&#39;Camembert&#39;</span>294<span class="gp">&gt;&gt;&gt; </span><span class="n">template</span> <span class="o">=</span> <span class="n">t</span><span class="s1">&#39;Ah! We do have </span><span class="si">{cheese}</span><span class="s1">.&#39;</span>295<span class="gp">&gt;&gt;&gt; </span><span class="n">template</span><span class="o">.</span><span class="n">strings</span>296<span class="go">(&#39;Ah! We do have &#39;, &#39;.&#39;)</span>297</pre></div>298</div>299<p>Empty strings <em>are</em> included in the tuple:</p>300<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">response</span> <span class="o">=</span> <span class="s1">&#39;We do have &#39;</span>301<span class="gp">&gt;&gt;&gt; </span><span class="n">cheese</span> <span class="o">=</span> <span class="s1">&#39;Camembert&#39;</span>302<span class="gp">&gt;&gt;&gt; </span><span class="n">template</span> <span class="o">=</span> <span class="n">t</span><span class="s1">&#39;Ah! </span><span class="si">{response}{cheese}</span><span class="s1">.&#39;</span>303<span class="gp">&gt;&gt;&gt; </span><span class="n">template</span><span class="o">.</span><span class="n">strings</span>304<span class="go">(&#39;Ah! &#39;, &#39;&#39;, &#39;.&#39;)</span>305</pre></div>306</div>307<p>The <code class="docutils literal notranslate"><span class="pre">strings</span></code> tuple is never empty, and always contains one more308string than the <code class="docutils literal notranslate"><span class="pre">interpolations</span></code> and <code class="docutils literal notranslate"><span class="pre">values</span></code> tuples:</p>309<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">t</span><span class="s1">&#39;&#39;</span><span class="o">.</span><span class="n">strings</span>310<span class="go">(&#39;&#39;,)</span>311<span class="gp">&gt;&gt;&gt; </span><span class="n">t</span><span class="s1">&#39;&#39;</span><span class="o">.</span><span class="n">values</span>312<span class="go">()</span>313<span class="gp">&gt;&gt;&gt; </span><span class="n">t</span><span class="s1">&#39;{&#39;</span><span class="n">cheese</span><span class="s1">&#39;}&#39;</span><span class="o">.</span><span class="n">strings</span>314<span class="go">(&#39;&#39;, &#39;&#39;)</span>315<span class="gp">&gt;&gt;&gt; </span><span class="n">t</span><span class="s1">&#39;{&#39;</span><span class="n">cheese</span><span class="s1">&#39;}&#39;</span><span class="o">.</span><span class="n">values</span>316<span class="go">(&#39;cheese&#39;,)</span>317</pre></div>318</div>319</dd></dl>320 321<dl class="py attribute">322<dt class="sig sig-object py" id="string.templatelib.Template.interpolations">323<span class="sig-name descname"><span class="pre">interpolations</span></span><em class="property"><span class="p"><span class="pre">:</span></span><span class="w"> </span><a class="reference internal" href="stdtypes.html#tuple" title="tuple"><span class="pre">tuple</span></a><span class="p"><span class="pre">[</span></span><a class="reference internal" href="#string.templatelib.Interpolation" title="string.templatelib.Interpolation"><span class="pre">Interpolation</span></a><span class="p"><span class="pre">,</span></span><span class="w"> </span><span class="p"><span class="pre">...</span></span><span class="p"><span class="pre">]</span></span></em><a class="headerlink" href="#string.templatelib.Template.interpolations" title="Link to this definition">¶</a></dt>324<dd><p>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> of the interpolations in the template.</p>325<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">cheese</span> <span class="o">=</span> <span class="s1">&#39;Camembert&#39;</span>326<span class="gp">&gt;&gt;&gt; </span><span class="n">template</span> <span class="o">=</span> <span class="n">t</span><span class="s1">&#39;Ah! We do have </span><span class="si">{cheese}</span><span class="s1">.&#39;</span>327<span class="gp">&gt;&gt;&gt; </span><span class="n">template</span><span class="o">.</span><span class="n">interpolations</span>328<span class="go">(Interpolation(&#39;Camembert&#39;, &#39;cheese&#39;, None, &#39;&#39;),)</span>329</pre></div>330</div>331<p>The <code class="docutils literal notranslate"><span class="pre">interpolations</span></code> tuple may be empty and always contains one fewer332values than the <code class="docutils literal notranslate"><span class="pre">strings</span></code> tuple:</p>333<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">t</span><span class="s1">&#39;Red Leicester&#39;</span><span class="o">.</span><span class="n">interpolations</span>334<span class="go">()</span>335</pre></div>336</div>337</dd></dl>338 339<dl class="py attribute">340<dt class="sig sig-object py" id="string.templatelib.Template.values">341<span class="sig-name descname"><span class="pre">values</span></span><em class="property"><span class="p"><span class="pre">:</span></span><span class="w"> </span><a class="reference internal" href="stdtypes.html#tuple" title="tuple"><span class="pre">tuple</span></a><span class="p"><span class="pre">[</span></span><a class="reference internal" href="functions.html#object" title="object"><span class="pre">object</span></a><span class="p"><span class="pre">,</span></span><span class="w"> </span><span class="p"><span class="pre">...</span></span><span class="p"><span class="pre">]</span></span></em><a class="headerlink" href="#string.templatelib.Template.values" title="Link to this definition">¶</a></dt>342<dd><p>A tuple of all interpolated values in the template.</p>343<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">cheese</span> <span class="o">=</span> <span class="s1">&#39;Camembert&#39;</span>344<span class="gp">&gt;&gt;&gt; </span><span class="n">template</span> <span class="o">=</span> <span class="n">t</span><span class="s1">&#39;Ah! We do have </span><span class="si">{cheese}</span><span class="s1">.&#39;</span>345<span class="gp">&gt;&gt;&gt; </span><span class="n">template</span><span class="o">.</span><span class="n">values</span>346<span class="go">(&#39;Camembert&#39;,)</span>347</pre></div>348</div>349<p>The <code class="docutils literal notranslate"><span class="pre">values</span></code> tuple always has the same length as the350<code class="docutils literal notranslate"><span class="pre">interpolations</span></code> tuple. It is always equivalent to351<code class="docutils literal notranslate"><span class="pre">tuple(i.value</span> <span class="pre">for</span> <span class="pre">i</span> <span class="pre">in</span> <span class="pre">template.interpolations)</span></code>.</p>352</dd></dl>353 354<p class="rubric">Methods</p>355<dl class="py method">356<dt class="sig sig-object py" id="string.templatelib.Template.__new__">357<span class="sig-name descname"><span class="pre">__new__</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="o"><span class="pre">*</span></span><span class="n"><span class="pre">args</span></span><span class="p"><span class="pre">:</span></span><span class="w"> </span><span class="n"><a class="reference internal" href="stdtypes.html#str" title="str"><span class="pre">str</span></a><span class="w"> </span><span class="p"><span class="pre">|</span></span><span class="w"> </span><a class="reference internal" href="#string.templatelib.Interpolation" title="string.templatelib.Interpolation"><span class="pre">Interpolation</span></a></span></em><span class="sig-paren">)</span><a class="headerlink" href="#string.templatelib.Template.__new__" title="Link to this definition">¶</a></dt>358<dd><p>While literal syntax is the most common way to create a <code class="xref py py-class docutils literal notranslate"><span class="pre">Template</span></code>,359it is also possible to create them directly using the constructor:</p>360<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="kn">from</span><span class="w"> </span><span class="nn">string.templatelib</span><span class="w"> </span><span class="kn">import</span> <span class="n">Interpolation</span><span class="p">,</span> <span class="n">Template</span>361<span class="gp">&gt;&gt;&gt; </span><span class="n">cheese</span> <span class="o">=</span> <span class="s1">&#39;Camembert&#39;</span>362<span class="gp">&gt;&gt;&gt; </span><span class="n">template</span> <span class="o">=</span> <span class="n">Template</span><span class="p">(</span>363<span class="gp">... </span>    <span class="s1">&#39;Ah! We do have &#39;</span><span class="p">,</span> <span class="n">Interpolation</span><span class="p">(</span><span class="n">cheese</span><span class="p">,</span> <span class="s1">&#39;cheese&#39;</span><span class="p">),</span> <span class="s1">&#39;.&#39;</span>364<span class="gp">... </span><span class="p">)</span>365<span class="gp">&gt;&gt;&gt; </span><span class="nb">list</span><span class="p">(</span><span class="n">template</span><span class="p">)</span>366<span class="go">[&#39;Ah! We do have &#39;, Interpolation(&#39;Camembert&#39;, &#39;cheese&#39;, None, &#39;&#39;), &#39;.&#39;]</span>367</pre></div>368</div>369<p>If multiple strings are passed consecutively, they will be concatenated370into a single value in the <a class="reference internal" href="#string.templatelib.Template.strings" title="string.templatelib.Template.strings"><code class="xref py py-attr docutils literal notranslate"><span class="pre">strings</span></code></a> attribute. For example,371the following code creates a <code class="xref py py-class docutils literal notranslate"><span class="pre">Template</span></code> with a single final string:</p>372<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="kn">from</span><span class="w"> </span><span class="nn">string.templatelib</span><span class="w"> </span><span class="kn">import</span> <span class="n">Template</span>373<span class="gp">&gt;&gt;&gt; </span><span class="n">template</span> <span class="o">=</span> <span class="n">Template</span><span class="p">(</span><span class="s1">&#39;Ah! We do have &#39;</span><span class="p">,</span> <span class="s1">&#39;Camembert&#39;</span><span class="p">,</span> <span class="s1">&#39;.&#39;</span><span class="p">)</span>374<span class="gp">&gt;&gt;&gt; </span><span class="n">template</span><span class="o">.</span><span class="n">strings</span>375<span class="go">(&#39;Ah! We do have Camembert.&#39;,)</span>376</pre></div>377</div>378<p>If multiple interpolations are passed consecutively, they will be treated379as separate interpolations and an empty string will be inserted between them.380For example, the following code creates a template with empty placeholders381in the <a class="reference internal" href="#string.templatelib.Template.strings" title="string.templatelib.Template.strings"><code class="xref py py-attr docutils literal notranslate"><span class="pre">strings</span></code></a> attribute:</p>382<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="kn">from</span><span class="w"> </span><span class="nn">string.templatelib</span><span class="w"> </span><span class="kn">import</span> <span class="n">Interpolation</span><span class="p">,</span> <span class="n">Template</span>383<span class="gp">&gt;&gt;&gt; </span><span class="n">template</span> <span class="o">=</span> <span class="n">Template</span><span class="p">(</span>384<span class="gp">... </span>    <span class="n">Interpolation</span><span class="p">(</span><span class="s1">&#39;Camembert&#39;</span><span class="p">,</span> <span class="s1">&#39;cheese&#39;</span><span class="p">),</span>385<span class="gp">... </span>    <span class="n">Interpolation</span><span class="p">(</span><span class="s1">&#39;.&#39;</span><span class="p">,</span> <span class="s1">&#39;punctuation&#39;</span><span class="p">),</span>386<span class="gp">... </span><span class="p">)</span>387<span class="gp">&gt;&gt;&gt; </span><span class="n">template</span><span class="o">.</span><span class="n">strings</span>388<span class="go">(&#39;&#39;, &#39;&#39;, &#39;&#39;)</span>389</pre></div>390</div>391</dd></dl>392 393<dl class="describe">394<dt class="sig sig-object">395<span class="sig-name descname"><span class="pre">iter(template)</span></span></dt>396<dd><p>Iterate over the template, yielding each non-empty string and397<a class="reference internal" href="#string.templatelib.Interpolation" title="string.templatelib.Interpolation"><code class="xref py py-class docutils literal notranslate"><span class="pre">Interpolation</span></code></a> in the correct order:</p>398<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">cheese</span> <span class="o">=</span> <span class="s1">&#39;Camembert&#39;</span>399<span class="gp">&gt;&gt;&gt; </span><span class="nb">list</span><span class="p">(</span><span class="n">t</span><span class="s1">&#39;Ah! We do have </span><span class="si">{cheese}</span><span class="s1">.&#39;</span><span class="p">)</span>400<span class="go">[&#39;Ah! We do have &#39;, Interpolation(&#39;Camembert&#39;, &#39;cheese&#39;, None, &#39;&#39;), &#39;.&#39;]</span>401</pre></div>402</div>403<div class="admonition caution">404<p class="admonition-title">Caution</p>405<p>Empty strings are <strong>not</strong> included in the iteration:</p>406<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">response</span> <span class="o">=</span> <span class="s1">&#39;We do have &#39;</span>407<span class="gp">&gt;&gt;&gt; </span><span class="n">cheese</span> <span class="o">=</span> <span class="s1">&#39;Camembert&#39;</span>408<span class="gp">&gt;&gt;&gt; </span><span class="nb">list</span><span class="p">(</span><span class="n">t</span><span class="s1">&#39;Ah! </span><span class="si">{response}{cheese}</span><span class="s1">.&#39;</span><span class="p">)</span>409<span class="go">[&#39;Ah! &#39;,</span>410<span class="go"> Interpolation(&#39;We do have &#39;, &#39;response&#39;, None, &#39;&#39;),</span>411<span class="go"> Interpolation(&#39;Camembert&#39;, &#39;cheese&#39;, None, &#39;&#39;),</span>412<span class="go"> &#39;.&#39;]</span>413</pre></div>414</div>415</div>416</dd></dl>417 418<dl class="describe">419<dt class="sig sig-object">420<span class="sig-name descname"><span class="pre">template</span> <span class="pre">+</span> <span class="pre">other</span></span></dt>421<dt class="sig sig-object">422<span class="sig-name descname"><span class="pre">template</span> <span class="pre">+=</span> <span class="pre">other</span></span></dt>423<dd><p>Concatenate this template with another, returning a new424<code class="xref py py-class docutils literal notranslate"><span class="pre">Template</span></code> instance:</p>425<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">cheese</span> <span class="o">=</span> <span class="s1">&#39;Camembert&#39;</span>426<span class="gp">&gt;&gt;&gt; </span><span class="nb">list</span><span class="p">(</span><span class="n">t</span><span class="s1">&#39;Ah! &#39;</span> <span class="o">+</span> <span class="n">t</span><span class="s1">&#39;We do have </span><span class="si">{cheese}</span><span class="s1">.&#39;</span><span class="p">)</span>427<span class="go">[&#39;Ah! We do have &#39;, Interpolation(&#39;Camembert&#39;, &#39;cheese&#39;, None, &#39;&#39;), &#39;.&#39;]</span>428</pre></div>429</div>430<p>Concatenating a <code class="xref py py-class docutils literal notranslate"><span class="pre">Template</span></code> and a <code class="docutils literal notranslate"><span class="pre">str</span></code> is <strong>not</strong> supported.431This is because it is unclear whether the string should be treated as432a static string or an interpolation.433If you want to concatenate a <code class="xref py py-class docutils literal notranslate"><span class="pre">Template</span></code> with a string,434you should either wrap the string directly in a <code class="xref py py-class docutils literal notranslate"><span class="pre">Template</span></code>435(to treat it as a static string)436or use an <code class="xref py py-class docutils literal notranslate"><span class="pre">Interpolation</span></code> (to treat it as dynamic):</p>437<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="kn">from</span><span class="w"> </span><span class="nn">string.templatelib</span><span class="w"> </span><span class="kn">import</span> <span class="n">Interpolation</span><span class="p">,</span> <span class="n">Template</span>438<span class="gp">&gt;&gt;&gt; </span><span class="n">template</span> <span class="o">=</span> <span class="n">t</span><span class="s1">&#39;Ah! &#39;</span>439<span class="gp">&gt;&gt;&gt; </span><span class="c1"># Treat &#39;We do have &#39; as a static string</span>440<span class="gp">&gt;&gt;&gt; </span><span class="n">template</span> <span class="o">+=</span> <span class="n">Template</span><span class="p">(</span><span class="s1">&#39;We do have &#39;</span><span class="p">)</span>441<span class="gp">&gt;&gt;&gt; </span><span class="c1"># Treat cheese as an interpolation</span>442<span class="gp">&gt;&gt;&gt; </span><span class="n">cheese</span> <span class="o">=</span> <span class="s1">&#39;Camembert&#39;</span>443<span class="gp">&gt;&gt;&gt; </span><span class="n">template</span> <span class="o">+=</span> <span class="n">Template</span><span class="p">(</span><span class="n">Interpolation</span><span class="p">(</span><span class="n">cheese</span><span class="p">,</span> <span class="s1">&#39;cheese&#39;</span><span class="p">))</span>444<span class="gp">&gt;&gt;&gt; </span><span class="nb">list</span><span class="p">(</span><span class="n">template</span><span class="p">)</span>445<span class="go">[&#39;Ah! We do have &#39;, Interpolation(&#39;Camembert&#39;, &#39;cheese&#39;, None, &#39;&#39;)]</span>446</pre></div>447</div>448</dd></dl>449 450</dd></dl>451 452<dl class="py class">453<dt class="sig sig-object py" id="string.templatelib.Interpolation">454<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">string.templatelib.</span></span><span class="sig-name descname"><span class="pre">Interpolation</span></span><a class="headerlink" href="#string.templatelib.Interpolation" title="Link to this definition">¶</a></dt>455<dd><p>The <code class="xref py py-class docutils literal notranslate"><span class="pre">Interpolation</span></code> type represents an expression inside a template string.456It is immutable, meaning that attributes of an interpolation cannot be reassigned.</p>457<p>Interpolations support pattern matching, allowing you to match against458their attributes with the <a class="reference internal" href="../reference/compound_stmts.html#match"><span class="std std-ref">match statement</span></a>:</p>459<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="kn">from</span><span class="w"> </span><span class="nn">string.templatelib</span><span class="w"> </span><span class="kn">import</span> <span class="n">Interpolation</span>460<span class="gp">&gt;&gt;&gt; </span><span class="n">interpolation</span> <span class="o">=</span> <span class="n">t</span><span class="s1">&#39;{1. + 2.:.2f}&#39;</span><span class="o">.</span><span class="n">interpolations</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span>461<span class="gp">&gt;&gt;&gt; </span><span class="n">interpolation</span>462<span class="go">Interpolation(3.0, &#39;1. + 2.&#39;, None, &#39;.2f&#39;)</span>463<span class="gp">&gt;&gt;&gt; </span><span class="k">match</span> <span class="n">interpolation</span><span class="p">:</span>464<span class="gp">... </span>    <span class="k">case</span> <span class="n">Interpolation</span><span class="p">(</span><span class="n">value</span><span class="p">,</span> <span class="n">expression</span><span class="p">,</span> <span class="n">conversion</span><span class="p">,</span> <span class="n">format_spec</span><span class="p">):</span>465<span class="gp">... </span>        <span class="nb">print</span><span class="p">(</span><span class="n">value</span><span class="p">,</span> <span class="n">expression</span><span class="p">,</span> <span class="n">conversion</span><span class="p">,</span> <span class="n">format_spec</span><span class="p">,</span> <span class="n">sep</span><span class="o">=</span><span class="s1">&#39; | &#39;</span><span class="p">)</span>466<span class="gp">...</span>467<span class="go">3.0 | 1. + 2. | None | .2f</span>468</pre></div>469</div>470<p class="rubric">Attributes</p>471<dl class="py attribute">472<dt class="sig sig-object py" id="string.templatelib.Interpolation.value">473<span class="sig-name descname"><span class="pre">value</span></span><em class="property"><span class="p"><span class="pre">:</span></span><span class="w"> </span><a class="reference internal" href="functions.html#object" title="object"><span class="pre">object</span></a></em><a class="headerlink" href="#string.templatelib.Interpolation.value" title="Link to this definition">¶</a></dt>474<dd><p>The evaluated value of the interpolation.</p>475<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">t</span><span class="s1">&#39;{1 + 2}&#39;</span><span class="o">.</span><span class="n">interpolations</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="o">.</span><span class="n">value</span>476<span class="go">3</span>477</pre></div>478</div>479</dd></dl>480 481<dl class="py attribute">482<dt class="sig sig-object py" id="string.templatelib.Interpolation.expression">483<span class="sig-name descname"><span class="pre">expression</span></span><em class="property"><span class="p"><span class="pre">:</span></span><span class="w"> </span><a class="reference internal" href="stdtypes.html#str" title="str"><span class="pre">str</span></a></em><a class="headerlink" href="#string.templatelib.Interpolation.expression" title="Link to this definition">¶</a></dt>484<dd><p>For interpolations created by t-string literals, <code class="xref py py-attr docutils literal notranslate"><span class="pre">expression</span></code>485is the expression text found inside the curly brackets (<code class="docutils literal notranslate"><span class="pre">{</span></code> &amp; <code class="docutils literal notranslate"><span class="pre">}</span></code>),486including any whitespace, excluding the curly brackets themselves,487and ending before the first <code class="docutils literal notranslate"><span class="pre">!</span></code>, <code class="docutils literal notranslate"><span class="pre">:</span></code>, or <code class="docutils literal notranslate"><span class="pre">=</span></code> if any is present.488For manually created interpolations, <code class="xref py py-attr docutils literal notranslate"><span class="pre">expression</span></code> is the arbitrary489string provided when constructing the interpolation instance.</p>490<p>We recommend using valid Python expressions or the empty string for the491<code class="docutils literal notranslate"><span class="pre">expression</span></code> field of manually created <code class="xref py py-class docutils literal notranslate"><span class="pre">Interpolation</span></code>492instances, although this is not enforced at runtime.</p>493<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">t</span><span class="s1">&#39;{1 + 2}&#39;</span><span class="o">.</span><span class="n">interpolations</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="o">.</span><span class="n">expression</span>494<span class="go">&#39;1 + 2&#39;</span>495</pre></div>496</div>497</dd></dl>498 499<dl class="py attribute">500<dt class="sig sig-object py" id="string.templatelib.Interpolation.conversion">501<span class="sig-name descname"><span class="pre">conversion</span></span><em class="property"><span class="p"><span class="pre">:</span></span><span class="w"> </span><a class="reference internal" href="typing.html#typing.Literal" title="typing.Literal"><span class="pre">Literal</span></a><span class="p"><span class="pre">[</span></span><span class="s"><span class="pre">'a'</span></span><span class="p"><span class="pre">,</span></span><span class="w"> </span><span class="s"><span class="pre">'r'</span></span><span class="p"><span class="pre">,</span></span><span class="w"> </span><span class="s"><span class="pre">'s'</span></span><span class="p"><span class="pre">]</span></span><span class="w"> </span><span class="p"><span class="pre">|</span></span><span class="w"> </span><a class="reference internal" href="constants.html#None" title="None"><span class="pre">None</span></a></em><a class="headerlink" href="#string.templatelib.Interpolation.conversion" title="Link to this definition">¶</a></dt>502<dd><p>The conversion to apply to the value, or <code class="docutils literal notranslate"><span class="pre">None</span></code>.</p>503<p>The <code class="xref py py-attr docutils literal notranslate"><span class="pre">conversion</span></code> is the optional conversion to apply504to the value:</p>505<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">t</span><span class="s1">&#39;{1 + 2!a}&#39;</span><span class="o">.</span><span class="n">interpolations</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="o">.</span><span class="n">conversion</span>506<span class="go">&#39;a&#39;</span>507</pre></div>508</div>509<div class="admonition note">510<p class="admonition-title">Note</p>511<p>Unlike f-strings, where conversions are applied automatically,512the expected behavior with t-strings is that code that <em>processes</em> the513<code class="xref py py-class docutils literal notranslate"><span class="pre">Template</span></code> will decide how to interpret and whether to apply514the <code class="xref py py-attr docutils literal notranslate"><span class="pre">conversion</span></code>.515For convenience, the <a class="reference internal" href="#string.templatelib.convert" title="string.templatelib.convert"><code class="xref py py-func docutils literal notranslate"><span class="pre">convert()</span></code></a> function can be used to mimic516f-string conversion semantics.</p>517</div>518</dd></dl>519 520<dl class="py attribute">521<dt class="sig sig-object py" id="string.templatelib.Interpolation.format_spec">522<span class="sig-name descname"><span class="pre">format_spec</span></span><em class="property"><span class="p"><span class="pre">:</span></span><span class="w"> </span><a class="reference internal" href="stdtypes.html#str" title="str"><span class="pre">str</span></a></em><a class="headerlink" href="#string.templatelib.Interpolation.format_spec" title="Link to this definition">¶</a></dt>523<dd><p>The format specification to apply to the value.</p>524<p>The <code class="xref py py-attr docutils literal notranslate"><span class="pre">format_spec</span></code> is an optional, arbitrary string525used as the format specification to present the value:</p>526<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">t</span><span class="s1">&#39;{1 + 2:.2f}&#39;</span><span class="o">.</span><span class="n">interpolations</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="o">.</span><span class="n">format_spec</span>527<span class="go">&#39;.2f&#39;</span>528</pre></div>529</div>530<div class="admonition note">531<p class="admonition-title">Note</p>532<p>Unlike f-strings, where format specifications are applied automatically533via the <a class="reference internal" href="functions.html#format" title="format"><code class="xref py py-func docutils literal notranslate"><span class="pre">format()</span></code></a> protocol, the expected behavior with534t-strings is that code that <em>processes</em> the interpolation will535decide how to interpret and whether to apply the format specification.536As a result, <code class="xref py py-attr docutils literal notranslate"><span class="pre">format_spec</span></code> values in interpolations537can be arbitrary strings,538including those that do not conform to the <code class="xref py py-func docutils literal notranslate"><span class="pre">format()</span></code> protocol.</p>539</div>540</dd></dl>541 542<p class="rubric">Methods</p>543<dl class="py method">544<dt class="sig sig-object py" id="string.templatelib.Interpolation.__new__">545<span class="sig-name descname"><span class="pre">__new__</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">value</span></span><span class="p"><span class="pre">:</span></span><span class="w"> </span><span class="n"><a class="reference internal" href="functions.html#object" title="object"><span class="pre">object</span></a></span></em>, <em class="sig-param"><span class="n"><span class="pre">expression</span></span><span class="p"><span class="pre">:</span></span><span class="w"> </span><span class="n"><a class="reference internal" href="stdtypes.html#str" title="str"><span class="pre">str</span></a></span></em>, <em class="sig-param"><span class="n"><span class="pre">conversion</span></span><span class="p"><span class="pre">:</span></span><span class="w"> </span><span class="n"><a class="reference internal" href="typing.html#typing.Literal" title="typing.Literal"><span class="pre">Literal</span></a><span class="p"><span class="pre">[</span></span><span class="s"><span class="pre">'a'</span></span><span class="p"><span class="pre">,</span></span><span class="w"> </span><span class="s"><span class="pre">'r'</span></span><span class="p"><span class="pre">,</span></span><span class="w"> </span><span class="s"><span class="pre">'s'</span></span><span class="p"><span class="pre">]</span></span><span class="w"> </span><span class="p"><span class="pre">|</span></span><span class="w"> </span><a class="reference internal" href="constants.html#None" title="None"><span class="pre">None</span></a></span><span class="w"> </span><span class="o"><span class="pre">=</span></span><span class="w"> </span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">format_spec</span></span><span class="p"><span class="pre">:</span></span><span class="w"> </span><span class="n"><a class="reference internal" href="stdtypes.html#str" title="str"><span class="pre">str</span></a></span><span class="w"> </span><span class="o"><span class="pre">=</span></span><span class="w"> </span><span class="default_value"><span class="pre">''</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#string.templatelib.Interpolation.__new__" title="Link to this definition">¶</a></dt>546<dd><p>Create a new <code class="xref py py-class docutils literal notranslate"><span class="pre">Interpolation</span></code> object from component parts.</p>547<dl class="field-list simple">548<dt class="field-odd">Parameters<span class="colon">:</span></dt>549<dd class="field-odd"><ul class="simple">550<li><p><strong>value</strong> – The evaluated, in-scope result of the interpolation.</p></li>551<li><p><strong>expression</strong> – The text of a valid Python expression,552or an empty string.</p></li>553<li><p><strong>conversion</strong> – The <a class="reference internal" href="string.html#formatstrings"><span class="std std-ref">conversion</span></a> to be used,554one of <code class="docutils literal notranslate"><span class="pre">None</span></code>, <code class="docutils literal notranslate"><span class="pre">'a'</span></code>, <code class="docutils literal notranslate"><span class="pre">'r'</span></code>, or <code class="docutils literal notranslate"><span class="pre">'s'</span></code>.</p></li>555<li><p><strong>format_spec</strong> – An optional, arbitrary string used as the556<a class="reference internal" href="string.html#formatspec"><span class="std std-ref">format specification</span></a> to present the value.</p></li>557</ul>558</dd>559</dl>560</dd></dl>561 562</dd></dl>563 564</section>565<section id="helper-functions">566<h2>Helper functions<a class="headerlink" href="#helper-functions" title="Link to this heading">¶</a></h2>567<dl class="py function">568<dt class="sig sig-object py" id="string.templatelib.convert">569<span class="sig-prename descclassname"><span class="pre">string.templatelib.</span></span><span class="sig-name descname"><span class="pre">convert</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="positional-only-separator o"><abbr title="Positional-only parameter separator (PEP 570)"><span class="pre">/</span></abbr></span></em>, <em class="sig-param"><span class="n"><span class="pre">conversion</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#string.templatelib.convert" title="Link to this definition">¶</a></dt>570<dd><p>Applies formatted string literal <a class="reference internal" href="string.html#formatstrings-conversion"><span class="std std-ref">conversion</span></a>571semantics to the given object <em>obj</em>.572This is frequently useful for custom template string processing logic.</p>573<p>Three conversion flags are currently supported:</p>574<ul class="simple">575<li><p><code class="docutils literal notranslate"><span class="pre">'s'</span></code> which calls <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-func docutils literal notranslate"><span class="pre">str()</span></code></a> on the value (like <code class="docutils literal notranslate"><span class="pre">!s</span></code>),</p></li>576<li><p><code class="docutils literal notranslate"><span class="pre">'r'</span></code> which calls <a class="reference internal" href="functions.html#repr" title="repr"><code class="xref py py-func docutils literal notranslate"><span class="pre">repr()</span></code></a> (like <code class="docutils literal notranslate"><span class="pre">!r</span></code>), and</p></li>577<li><p><code class="docutils literal notranslate"><span class="pre">'a'</span></code> which calls <a class="reference internal" href="functions.html#ascii" title="ascii"><code class="xref py py-func docutils literal notranslate"><span class="pre">ascii()</span></code></a> (like <code class="docutils literal notranslate"><span class="pre">!a</span></code>).</p></li>578</ul>579<p>If the conversion flag is <code class="docutils literal notranslate"><span class="pre">None</span></code>, <em>obj</em> is returned unchanged.</p>580</dd></dl>581 582</section>583</section>584 585 586            <div class="clearer"></div>587          </div>588        </div>589      </div>590      <div class="sphinxsidebar" role="navigation" aria-label="Main">591        <div class="sphinxsidebarwrapper">592  <div>593    <h3><a href="../contents.html">Table of Contents</a></h3>594    <ul>595<li><a class="reference internal" href="#"><code class="xref py py-mod docutils literal notranslate"><span class="pre">string.templatelib</span></code> — Support for template string literals</a><ul>596<li><a class="reference internal" href="#template-strings">Template strings</a></li>597<li><a class="reference internal" href="#types">Types</a></li>598<li><a class="reference internal" href="#helper-functions">Helper functions</a></li>599</ul>600</li>601</ul>602 603  </div>604  <div>605    <h4>Previous topic</h4>606    <p class="topless"><a href="string.html"607                          title="previous chapter"><code class="xref py py-mod docutils literal notranslate"><span class="pre">string</span></code> — Common string operations</a></p>608  </div>609  <div>610    <h4>Next topic</h4>611    <p class="topless"><a href="re.html"612                          title="next chapter"><code class="xref py py-mod docutils literal notranslate"><span class="pre">re</span></code> — Regular expression operations</a></p>613  </div>614  <script>615    document.addEventListener('DOMContentLoaded', () => {616 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