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nav-item-3"><a href="asyncio.html" accesskey="U"><code class="xref py py-mod docutils literal notranslate"><span class="pre">asyncio</span></code> — Asynchronous I/O</a> &#187;</li>196        <li class="nav-item nav-item-this"><a href="">Streams</a></li>197                <li class="right">198                    199 200    <div class="inline-search" role="search">201        <form class="inline-search" action="../search.html" method="get">202          <input placeholder="Quick search" aria-label="Quick search" type="search" name="q" id="search-box">203          <input type="submit" value="Go">204        </form>205    </div>206                     |207                </li>208            <li class="right">209<label class="theme-selector-label">210    Theme211    <select class="theme-selector" oninput="activateTheme(this.value)">212        <option value="auto" selected>Auto</option>213        <option value="light">Light</option>214        <option value="dark">Dark</option>215    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Streams allow sending and receiving data without232using callbacks or low-level protocols and transports.</p>233<p id="asyncio-example-stream">Here is an example of a TCP echo client written using asyncio234streams:</p>235<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span><span class="w"> </span><span class="nn">asyncio</span>236 237<span class="k">async</span> <span class="k">def</span><span class="w"> </span><span class="nf">tcp_echo_client</span><span class="p">(</span><span class="n">message</span><span class="p">):</span>238    <span class="n">reader</span><span class="p">,</span> <span class="n">writer</span> <span class="o">=</span> <span class="k">await</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">open_connection</span><span class="p">(</span>239        <span class="s1">&#39;127.0.0.1&#39;</span><span class="p">,</span> <span class="mi">8888</span><span class="p">)</span>240 241    <span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s1">&#39;Send: </span><span class="si">{</span><span class="n">message</span><span class="si">!r}</span><span class="s1">&#39;</span><span class="p">)</span>242    <span class="n">writer</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="n">message</span><span class="o">.</span><span class="n">encode</span><span class="p">())</span>243    <span class="k">await</span> <span class="n">writer</span><span class="o">.</span><span class="n">drain</span><span class="p">()</span>244 245    <span class="n">data</span> <span class="o">=</span> <span class="k">await</span> <span class="n">reader</span><span class="o">.</span><span class="n">read</span><span class="p">(</span><span class="mi">100</span><span class="p">)</span>246    <span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s1">&#39;Received: </span><span class="si">{</span><span class="n">data</span><span class="o">.</span><span class="n">decode</span><span class="p">()</span><span class="si">!r}</span><span class="s1">&#39;</span><span class="p">)</span>247 248    <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;Close the connection&#39;</span><span class="p">)</span>249    <span class="n">writer</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>250    <span class="k">await</span> <span class="n">writer</span><span class="o">.</span><span class="n">wait_closed</span><span class="p">()</span>251 252<span class="n">asyncio</span><span class="o">.</span><span class="n">run</span><span class="p">(</span><span class="n">tcp_echo_client</span><span class="p">(</span><span class="s1">&#39;Hello World!&#39;</span><span class="p">))</span>253</pre></div>254</div>255<p>See also the <a class="reference internal" href="#examples">Examples</a> section below.</p>256<p class="rubric">Stream Functions</p>257<p>The following top-level asyncio functions can be used to create258and work with streams:</p>259<dl class="py function">260<dt class="sig sig-object py" id="asyncio.open_connection">261<em class="property"><span class="k"><span class="pre">async</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">asyncio.</span></span><span class="sig-name descname"><span class="pre">open_connection</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">host</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">port</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="keyword-only-separator o"><abbr title="Keyword-only parameters separator (PEP 3102)"><span class="pre">*</span></abbr></span></em>, <em class="sig-param"><span class="n"><span class="pre">limit</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">ssl</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">family</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">0</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">proto</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">0</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">flags</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">0</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">sock</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">local_addr</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">server_hostname</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">ssl_handshake_timeout</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">ssl_shutdown_timeout</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">happy_eyeballs_delay</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">interleave</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="#asyncio.open_connection" title="Link to this definition">¶</a></dt>262<dd><p>Establish a network connection and return a pair of263<code class="docutils literal notranslate"><span class="pre">(reader,</span> <span class="pre">writer)</span></code> objects.</p>264<p>The returned <em>reader</em> and <em>writer</em> objects are instances of265<a class="reference internal" href="#asyncio.StreamReader" title="asyncio.StreamReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReader</span></code></a> and <a class="reference internal" href="#asyncio.StreamWriter" title="asyncio.StreamWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamWriter</span></code></a> classes.</p>266<p><em>limit</em> determines the buffer size limit used by the267returned <a class="reference internal" href="#asyncio.StreamReader" title="asyncio.StreamReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReader</span></code></a> instance.  By default the <em>limit</em>268is set to 64 KiB.</p>269<p>The rest of the arguments are passed directly to270<a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.create_connection" title="asyncio.loop.create_connection"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.create_connection()</span></code></a>.</p>271<div class="admonition note">272<p class="admonition-title">Note</p>273<p>The <em>sock</em> argument transfers ownership of the socket to the274<a class="reference internal" href="#asyncio.StreamWriter" title="asyncio.StreamWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamWriter</span></code></a> created. To close the socket, call its275<a class="reference internal" href="#asyncio.StreamWriter.close" title="asyncio.StreamWriter.close"><code class="xref py py-meth docutils literal notranslate"><span class="pre">close()</span></code></a> method.</p>276</div>277<div class="versionchanged">278<p><span class="versionmodified changed">Changed in version 3.7: </span>Added the <em>ssl_handshake_timeout</em> parameter.</p>279</div>280<div class="versionchanged">281<p><span class="versionmodified changed">Changed in version 3.8: </span>Added the <em>happy_eyeballs_delay</em> and <em>interleave</em> parameters.</p>282</div>283<div class="versionchanged">284<p><span class="versionmodified changed">Changed in version 3.10: </span>Removed the <em>loop</em> parameter.</p>285</div>286<div class="versionchanged">287<p><span class="versionmodified changed">Changed in version 3.11: </span>Added the <em>ssl_shutdown_timeout</em> parameter.</p>288</div>289</dd></dl>290 291<dl class="py function">292<dt class="sig sig-object py" id="asyncio.start_server">293<em class="property"><span class="k"><span class="pre">async</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">asyncio.</span></span><span class="sig-name descname"><span class="pre">start_server</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">client_connected_cb</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">host</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">port</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="keyword-only-separator o"><abbr title="Keyword-only parameters separator (PEP 3102)"><span class="pre">*</span></abbr></span></em>, <em class="sig-param"><span class="n"><span class="pre">limit</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">family</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">socket.AF_UNSPEC</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">flags</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">socket.AI_PASSIVE</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">sock</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">backlog</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">100</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">ssl</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">reuse_address</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">reuse_port</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">keep_alive</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">ssl_handshake_timeout</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">ssl_shutdown_timeout</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">start_serving</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="#asyncio.start_server" title="Link to this definition">¶</a></dt>294<dd><p>Start a socket server.</p>295<p>The <em>client_connected_cb</em> callback is called whenever a new client296connection is established.  It receives a <code class="docutils literal notranslate"><span class="pre">(reader,</span> <span class="pre">writer)</span></code> pair297as two arguments, instances of the <a class="reference internal" href="#asyncio.StreamReader" title="asyncio.StreamReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReader</span></code></a> and298<a class="reference internal" href="#asyncio.StreamWriter" title="asyncio.StreamWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamWriter</span></code></a> classes.</p>299<p><em>client_connected_cb</em> can be a plain callable or a300<a class="reference internal" href="asyncio-task.html#coroutine"><span class="std std-ref">coroutine function</span></a>; if it is a coroutine function,301it will be automatically scheduled as a <a class="reference internal" href="asyncio-task.html#asyncio.Task" title="asyncio.Task"><code class="xref py py-class docutils literal notranslate"><span class="pre">Task</span></code></a>.</p>302<p><em>limit</em> determines the buffer size limit used by the303returned <a class="reference internal" href="#asyncio.StreamReader" title="asyncio.StreamReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReader</span></code></a> instance.  By default the <em>limit</em>304is set to 64 KiB.</p>305<p>The rest of the arguments are passed directly to306<a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.create_server" title="asyncio.loop.create_server"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.create_server()</span></code></a>.</p>307<div class="admonition note">308<p class="admonition-title">Note</p>309<p>The <em>sock</em> argument transfers ownership of the socket to the310server created. To close the socket, call the server’s311<a class="reference internal" href="asyncio-eventloop.html#asyncio.Server.close" title="asyncio.Server.close"><code class="xref py py-meth docutils literal notranslate"><span class="pre">close()</span></code></a> method.</p>312</div>313<div class="versionchanged">314<p><span class="versionmodified changed">Changed in version 3.7: </span>Added the <em>ssl_handshake_timeout</em> and <em>start_serving</em> parameters.</p>315</div>316<div class="versionchanged">317<p><span class="versionmodified changed">Changed in version 3.10: </span>Removed the <em>loop</em> parameter.</p>318</div>319<div class="versionchanged">320<p><span class="versionmodified changed">Changed in version 3.11: </span>Added the <em>ssl_shutdown_timeout</em> parameter.</p>321</div>322<div class="versionchanged">323<p><span class="versionmodified changed">Changed in version 3.13: </span>Added the <em>keep_alive</em> parameter.</p>324</div>325</dd></dl>326 327<p class="rubric">Unix Sockets</p>328<dl class="py function">329<dt class="sig sig-object py" id="asyncio.open_unix_connection">330<em class="property"><span class="k"><span class="pre">async</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">asyncio.</span></span><span class="sig-name descname"><span class="pre">open_unix_connection</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">path</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="keyword-only-separator o"><abbr title="Keyword-only parameters separator (PEP 3102)"><span class="pre">*</span></abbr></span></em>, <em class="sig-param"><span class="n"><span class="pre">limit</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">ssl</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">sock</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">server_hostname</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">ssl_handshake_timeout</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">ssl_shutdown_timeout</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="#asyncio.open_unix_connection" title="Link to this definition">¶</a></dt>331<dd><p>Establish a Unix socket connection and return a pair of332<code class="docutils literal notranslate"><span class="pre">(reader,</span> <span class="pre">writer)</span></code>.</p>333<p>Similar to <a class="reference internal" href="#asyncio.open_connection" title="asyncio.open_connection"><code class="xref py py-func docutils literal notranslate"><span class="pre">open_connection()</span></code></a> but operates on Unix sockets.</p>334<p>See also the documentation of <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.create_unix_connection" title="asyncio.loop.create_unix_connection"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.create_unix_connection()</span></code></a>.</p>335<div class="admonition note">336<p class="admonition-title">Note</p>337<p>The <em>sock</em> argument transfers ownership of the socket to the338<a class="reference internal" href="#asyncio.StreamWriter" title="asyncio.StreamWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamWriter</span></code></a> created. To close the socket, call its339<a class="reference internal" href="#asyncio.StreamWriter.close" title="asyncio.StreamWriter.close"><code class="xref py py-meth docutils literal notranslate"><span class="pre">close()</span></code></a> method.</p>340</div>341<div class="availability docutils container">342<p><a class="reference internal" href="intro.html#availability"><span class="std std-ref">Availability</span></a>: Unix.</p>343</div>344<div class="versionchanged">345<p><span class="versionmodified changed">Changed in version 3.7: </span>Added the <em>ssl_handshake_timeout</em> parameter.346The <em>path</em> parameter can now be a <a class="reference internal" href="../glossary.html#term-path-like-object"><span class="xref std std-term">path-like object</span></a></p>347</div>348<div class="versionchanged">349<p><span class="versionmodified changed">Changed in version 3.10: </span>Removed the <em>loop</em> parameter.</p>350</div>351<div class="versionchanged">352<p><span class="versionmodified changed">Changed in version 3.11: </span>Added the <em>ssl_shutdown_timeout</em> parameter.</p>353</div>354</dd></dl>355 356<dl class="py function">357<dt class="sig sig-object py" id="asyncio.start_unix_server">358<em class="property"><span class="k"><span class="pre">async</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">asyncio.</span></span><span class="sig-name descname"><span class="pre">start_unix_server</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">client_connected_cb</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">path</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="keyword-only-separator o"><abbr title="Keyword-only parameters separator (PEP 3102)"><span class="pre">*</span></abbr></span></em>, <em class="sig-param"><span class="n"><span class="pre">limit</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">sock</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">backlog</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">100</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">ssl</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">ssl_handshake_timeout</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">ssl_shutdown_timeout</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">start_serving</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">True</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">cleanup_socket</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="#asyncio.start_unix_server" title="Link to this definition">¶</a></dt>359<dd><p>Start a Unix socket server.</p>360<p>Similar to <a class="reference internal" href="#asyncio.start_server" title="asyncio.start_server"><code class="xref py py-func docutils literal notranslate"><span class="pre">start_server()</span></code></a> but works with Unix sockets.</p>361<p>If <em>cleanup_socket</em> is true then the Unix socket will automatically362be removed from the filesystem when the server is closed, unless the363socket has been replaced after the server has been created.</p>364<p>See also the documentation of <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.create_unix_server" title="asyncio.loop.create_unix_server"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.create_unix_server()</span></code></a>.</p>365<div class="admonition note">366<p class="admonition-title">Note</p>367<p>The <em>sock</em> argument transfers ownership of the socket to the368server created. To close the socket, call the server’s369<a class="reference internal" href="asyncio-eventloop.html#asyncio.Server.close" title="asyncio.Server.close"><code class="xref py py-meth docutils literal notranslate"><span class="pre">close()</span></code></a> method.</p>370</div>371<div class="availability docutils container">372<p><a class="reference internal" href="intro.html#availability"><span class="std std-ref">Availability</span></a>: Unix.</p>373</div>374<div class="versionchanged">375<p><span class="versionmodified changed">Changed in version 3.7: </span>Added the <em>ssl_handshake_timeout</em> and <em>start_serving</em> parameters.376The <em>path</em> parameter can now be a <a class="reference internal" href="../glossary.html#term-path-like-object"><span class="xref std std-term">path-like object</span></a>.</p>377</div>378<div class="versionchanged">379<p><span class="versionmodified changed">Changed in version 3.10: </span>Removed the <em>loop</em> parameter.</p>380</div>381<div class="versionchanged">382<p><span class="versionmodified changed">Changed in version 3.11: </span>Added the <em>ssl_shutdown_timeout</em> parameter.</p>383</div>384<div class="versionchanged">385<p><span class="versionmodified changed">Changed in version 3.13: </span>Added the <em>cleanup_socket</em> parameter.</p>386</div>387</dd></dl>388 389<section id="streamreader">390<h2>StreamReader<a class="headerlink" href="#streamreader" title="Link to this heading">¶</a></h2>391<dl class="py class">392<dt class="sig sig-object py" id="asyncio.StreamReader">393<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">asyncio.</span></span><span class="sig-name descname"><span class="pre">StreamReader</span></span><a class="headerlink" href="#asyncio.StreamReader" title="Link to this definition">¶</a></dt>394<dd><p>Represents a reader object that provides APIs to read data395from the IO stream. As an <a class="reference internal" href="../glossary.html#term-asynchronous-iterable"><span class="xref std std-term">asynchronous iterable</span></a>, the396object supports the <a class="reference internal" href="../reference/compound_stmts.html#async-for"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">async</span> <span class="pre">for</span></code></a> statement.</p>397<p>It is not recommended to instantiate <em>StreamReader</em> objects398directly; use <a class="reference internal" href="#asyncio.open_connection" title="asyncio.open_connection"><code class="xref py py-func docutils literal notranslate"><span class="pre">open_connection()</span></code></a> and <a class="reference internal" href="#asyncio.start_server" title="asyncio.start_server"><code class="xref py py-func docutils literal notranslate"><span class="pre">start_server()</span></code></a>399instead.</p>400<dl class="py method">401<dt class="sig sig-object py" id="asyncio.StreamReader.feed_eof">402<span class="sig-name descname"><span class="pre">feed_eof</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.StreamReader.feed_eof" title="Link to this definition">¶</a></dt>403<dd><p>Acknowledge the EOF.</p>404</dd></dl>405 406<dl class="py method">407<dt class="sig sig-object py" id="asyncio.StreamReader.read">408<em class="property"><span class="k"><span class="pre">async</span></span><span class="w"> </span></em><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">n</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="#asyncio.StreamReader.read" title="Link to this definition">¶</a></dt>409<dd><p>Read up to <em>n</em> bytes from the stream.</p>410<p>If <em>n</em> is not provided or set to <code class="docutils literal notranslate"><span class="pre">-1</span></code>,411read until EOF, then return all read <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>.412If EOF was received and the internal buffer is empty,413return an empty <code class="docutils literal notranslate"><span class="pre">bytes</span></code> object.</p>414<p>If <em>n</em> is <code class="docutils literal notranslate"><span class="pre">0</span></code>, return an empty <code class="docutils literal notranslate"><span class="pre">bytes</span></code> object immediately.</p>415<p>If <em>n</em> is positive, return at most <em>n</em> available <code class="docutils literal notranslate"><span class="pre">bytes</span></code>416as soon as at least 1 byte is available in the internal buffer.417If EOF is received before any byte is read, return an empty418<code class="docutils literal notranslate"><span class="pre">bytes</span></code> object.</p>419</dd></dl>420 421<dl class="py method">422<dt class="sig sig-object py" id="asyncio.StreamReader.readline">423<em class="property"><span class="k"><span class="pre">async</span></span><span class="w"> </span></em><span class="sig-name descname"><span class="pre">readline</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.StreamReader.readline" title="Link to this definition">¶</a></dt>424<dd><p>Read one line, where “line” is a sequence of bytes425ending with <code class="docutils literal notranslate"><span class="pre">\n</span></code>.</p>426<p>If EOF is received and <code class="docutils literal notranslate"><span class="pre">\n</span></code> was not found, the method427returns partially read data.</p>428<p>If EOF is received and the internal buffer is empty,429return an empty <code class="docutils literal notranslate"><span class="pre">bytes</span></code> object.</p>430</dd></dl>431 432<dl class="py method">433<dt class="sig sig-object py" id="asyncio.StreamReader.readexactly">434<em class="property"><span class="k"><span class="pre">async</span></span><span class="w"> </span></em><span class="sig-name descname"><span class="pre">readexactly</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">n</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.StreamReader.readexactly" title="Link to this definition">¶</a></dt>435<dd><p>Read exactly <em>n</em> bytes.</p>436<p>Raise an <a class="reference internal" href="asyncio-exceptions.html#asyncio.IncompleteReadError" title="asyncio.IncompleteReadError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">IncompleteReadError</span></code></a> if EOF is reached before <em>n</em>437can be read.  Use the <a class="reference internal" href="asyncio-exceptions.html#asyncio.IncompleteReadError.partial" title="asyncio.IncompleteReadError.partial"><code class="xref py py-attr docutils literal notranslate"><span class="pre">IncompleteReadError.partial</span></code></a>438attribute to get the partially read data.</p>439</dd></dl>440 441<dl class="py method">442<dt class="sig sig-object py" id="asyncio.StreamReader.readuntil">443<em class="property"><span class="k"><span class="pre">async</span></span><span class="w"> </span></em><span class="sig-name descname"><span class="pre">readuntil</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">separator</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">b'\n'</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.StreamReader.readuntil" title="Link to this definition">¶</a></dt>444<dd><p>Read data from the stream until <em>separator</em> is found.</p>445<p>On success, the data and separator will be removed from the446internal buffer (consumed). Returned data will include the447separator at the end.</p>448<p>If the amount of data read exceeds the configured stream limit, a449<a class="reference internal" href="asyncio-exceptions.html#asyncio.LimitOverrunError" title="asyncio.LimitOverrunError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">LimitOverrunError</span></code></a> exception is raised, and the data450is left in the internal buffer and can be read again.</p>451<p>If EOF is reached before the complete separator is found,452an <a class="reference internal" href="asyncio-exceptions.html#asyncio.IncompleteReadError" title="asyncio.IncompleteReadError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">IncompleteReadError</span></code></a> exception is raised, and the internal453buffer is reset.  The <a class="reference internal" href="asyncio-exceptions.html#asyncio.IncompleteReadError.partial" title="asyncio.IncompleteReadError.partial"><code class="xref py py-attr docutils literal notranslate"><span class="pre">IncompleteReadError.partial</span></code></a> attribute454may contain a portion of the separator.</p>455<p>The <em>separator</em> may also be a tuple of separators. In this456case the return value will be the shortest possible that has any457separator as the suffix. For the purposes of <a class="reference internal" href="asyncio-exceptions.html#asyncio.LimitOverrunError" title="asyncio.LimitOverrunError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">LimitOverrunError</span></code></a>,458the shortest possible separator is considered to be the one that459matched.</p>460<div class="versionadded">461<p><span class="versionmodified added">Added in version 3.5.2.</span></p>462</div>463<div class="versionchanged">464<p><span class="versionmodified changed">Changed in version 3.13: </span>The <em>separator</em> parameter may now be 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> of465separators.</p>466</div>467</dd></dl>468 469<dl class="py method">470<dt class="sig sig-object py" id="asyncio.StreamReader.at_eof">471<span class="sig-name descname"><span class="pre">at_eof</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.StreamReader.at_eof" title="Link to this definition">¶</a></dt>472<dd><p>Return <code class="docutils literal notranslate"><span class="pre">True</span></code> if the buffer is empty and <a class="reference internal" href="#asyncio.StreamReader.feed_eof" title="asyncio.StreamReader.feed_eof"><code class="xref py py-meth docutils literal notranslate"><span class="pre">feed_eof()</span></code></a>473was called.</p>474</dd></dl>475 476</dd></dl>477 478</section>479<section id="streamwriter">480<h2>StreamWriter<a class="headerlink" href="#streamwriter" title="Link to this heading">¶</a></h2>481<dl class="py class">482<dt class="sig sig-object py" id="asyncio.StreamWriter">483<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">asyncio.</span></span><span class="sig-name descname"><span class="pre">StreamWriter</span></span><a class="headerlink" href="#asyncio.StreamWriter" title="Link to this definition">¶</a></dt>484<dd><p>Represents a writer object that provides APIs to write data485to the IO stream.</p>486<p>It is not recommended to instantiate <em>StreamWriter</em> objects487directly; use <a class="reference internal" href="#asyncio.open_connection" title="asyncio.open_connection"><code class="xref py py-func docutils literal notranslate"><span class="pre">open_connection()</span></code></a> and <a class="reference internal" href="#asyncio.start_server" title="asyncio.start_server"><code class="xref py py-func docutils literal notranslate"><span class="pre">start_server()</span></code></a>488instead.</p>489<dl class="py method">490<dt class="sig sig-object py" id="asyncio.StreamWriter.write">491<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">data</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.StreamWriter.write" title="Link to this definition">¶</a></dt>492<dd><p>The method attempts to write the <em>data</em> to the underlying socket immediately.493If that fails, the data is queued in an internal write buffer until it can be494sent.</p>495<p>The <em>data</em> buffer should be a bytes, bytearray, or C-contiguous one-dimensional496memoryview object.</p>497<p>The method should be used along with the <code class="docutils literal notranslate"><span class="pre">drain()</span></code> method:</p>498<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">stream</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="n">data</span><span class="p">)</span>499<span class="k">await</span> <span class="n">stream</span><span class="o">.</span><span class="n">drain</span><span class="p">()</span>500</pre></div>501</div>502</dd></dl>503 504<dl class="py method">505<dt class="sig sig-object py" id="asyncio.StreamWriter.writelines">506<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">data</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.StreamWriter.writelines" title="Link to this definition">¶</a></dt>507<dd><p>The method writes a list (or any iterable) of bytes to the underlying socket508immediately.509If that fails, the data is queued in an internal write buffer until it can be510sent.</p>511<p>The method should be used along with the <code class="docutils literal notranslate"><span class="pre">drain()</span></code> method:</p>512<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">stream</span><span class="o">.</span><span class="n">writelines</span><span class="p">(</span><span class="n">lines</span><span class="p">)</span>513<span class="k">await</span> <span class="n">stream</span><span class="o">.</span><span class="n">drain</span><span class="p">()</span>514</pre></div>515</div>516</dd></dl>517 518<dl class="py method">519<dt class="sig sig-object py" id="asyncio.StreamWriter.close">520<span class="sig-name descname"><span class="pre">close</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.StreamWriter.close" title="Link to this definition">¶</a></dt>521<dd><p>The method closes the stream and the underlying socket.</p>522<p>The method should be used, though not mandatory,523along with the <code class="docutils literal notranslate"><span class="pre">wait_closed()</span></code> method:</p>524<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">stream</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>525<span class="k">await</span> <span class="n">stream</span><span class="o">.</span><span class="n">wait_closed</span><span class="p">()</span>526</pre></div>527</div>528</dd></dl>529 530<dl class="py method">531<dt class="sig sig-object py" id="asyncio.StreamWriter.can_write_eof">532<span class="sig-name descname"><span class="pre">can_write_eof</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.StreamWriter.can_write_eof" title="Link to this definition">¶</a></dt>533<dd><p>Return <code class="docutils literal notranslate"><span class="pre">True</span></code> if the underlying transport supports534the <a class="reference internal" href="#asyncio.StreamWriter.write_eof" title="asyncio.StreamWriter.write_eof"><code class="xref py py-meth docutils literal notranslate"><span class="pre">write_eof()</span></code></a> method, <code class="docutils literal notranslate"><span class="pre">False</span></code> otherwise.</p>535</dd></dl>536 537<dl class="py method">538<dt class="sig sig-object py" id="asyncio.StreamWriter.write_eof">539<span class="sig-name descname"><span class="pre">write_eof</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.StreamWriter.write_eof" title="Link to this definition">¶</a></dt>540<dd><p>Close the write end of the stream after the buffered write541data is flushed.</p>542</dd></dl>543 544<dl class="py attribute">545<dt class="sig sig-object py" id="asyncio.StreamWriter.transport">546<span class="sig-name descname"><span class="pre">transport</span></span><a class="headerlink" href="#asyncio.StreamWriter.transport" title="Link to this definition">¶</a></dt>547<dd><p>Return the underlying asyncio transport.</p>548</dd></dl>549 550<dl class="py method">551<dt class="sig sig-object py" id="asyncio.StreamWriter.get_extra_info">552<span class="sig-name descname"><span class="pre">get_extra_info</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">default</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="#asyncio.StreamWriter.get_extra_info" title="Link to this definition">¶</a></dt>553<dd><p>Access optional transport information; see554<a class="reference internal" href="asyncio-protocol.html#asyncio.BaseTransport.get_extra_info" title="asyncio.BaseTransport.get_extra_info"><code class="xref py py-meth docutils literal notranslate"><span class="pre">BaseTransport.get_extra_info()</span></code></a> for details.</p>555</dd></dl>556 557<dl class="py method">558<dt class="sig sig-object py" id="asyncio.StreamWriter.drain">559<em class="property"><span class="k"><span class="pre">async</span></span><span class="w"> </span></em><span class="sig-name descname"><span class="pre">drain</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.StreamWriter.drain" title="Link to this definition">¶</a></dt>560<dd><p>Wait until it is appropriate to resume writing to the stream.561Example:</p>562<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">writer</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="n">data</span><span class="p">)</span>563<span class="k">await</span> <span class="n">writer</span><span class="o">.</span><span class="n">drain</span><span class="p">()</span>564</pre></div>565</div>566<p>This is a flow control method that interacts with the underlying567IO write buffer.  When the size of the buffer reaches568the high watermark, <em>drain()</em> blocks until the size of the569buffer is drained down to the low watermark and writing can570be resumed.  When there is nothing to wait for, the <code class="xref py py-meth docutils literal notranslate"><span class="pre">drain()</span></code>571returns immediately.</p>572</dd></dl>573 574<dl class="py method">575<dt class="sig sig-object py" id="asyncio.StreamWriter.start_tls">576<em class="property"><span class="k"><span class="pre">async</span></span><span class="w"> </span></em><span class="sig-name descname"><span class="pre">start_tls</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">sslcontext</span></span></em>, <em class="sig-param"><span class="keyword-only-separator o"><abbr title="Keyword-only parameters separator (PEP 3102)"><span class="pre">*</span></abbr></span></em>, <em class="sig-param"><span class="n"><span class="pre">server_hostname</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">ssl_handshake_timeout</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">ssl_shutdown_timeout</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="#asyncio.StreamWriter.start_tls" title="Link to this definition">¶</a></dt>577<dd><p>Upgrade an existing stream-based connection to TLS.</p>578<p>Parameters:</p>579<ul class="simple">580<li><p><em>sslcontext</em>: a configured instance of <a class="reference internal" href="ssl.html#ssl.SSLContext" title="ssl.SSLContext"><code class="xref py py-class docutils literal notranslate"><span class="pre">SSLContext</span></code></a>.</p></li>581<li><p><em>server_hostname</em>: sets or overrides the host name that the target582server’s certificate will be matched against.</p></li>583<li><p><em>ssl_handshake_timeout</em> is the time in seconds to wait for the TLS584handshake to complete before aborting the connection.  <code class="docutils literal notranslate"><span class="pre">60.0</span></code> seconds585if <code class="docutils literal notranslate"><span class="pre">None</span></code> (default).</p></li>586<li><p><em>ssl_shutdown_timeout</em> is the time in seconds to wait for the SSL shutdown587to complete before aborting the connection. <code class="docutils literal notranslate"><span class="pre">30.0</span></code> seconds if <code class="docutils literal notranslate"><span class="pre">None</span></code>588(default).</p></li>589</ul>590<div class="versionadded">591<p><span class="versionmodified added">Added in version 3.11.</span></p>592</div>593<div class="versionchanged">594<p><span class="versionmodified changed">Changed in version 3.12: </span>Added the <em>ssl_shutdown_timeout</em> parameter.</p>595</div>596</dd></dl>597 598<dl class="py method">599<dt class="sig sig-object py" id="asyncio.StreamWriter.is_closing">600<span class="sig-name descname"><span class="pre">is_closing</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.StreamWriter.is_closing" title="Link to this definition">¶</a></dt>601<dd><p>Return <code class="docutils literal notranslate"><span class="pre">True</span></code> if the stream is closed or in the process of602being closed.</p>603<div class="versionadded">604<p><span class="versionmodified added">Added in version 3.7.</span></p>605</div>606</dd></dl>607 608<dl class="py method">609<dt class="sig sig-object py" id="asyncio.StreamWriter.wait_closed">610<em class="property"><span class="k"><span class="pre">async</span></span><span class="w"> </span></em><span class="sig-name descname"><span class="pre">wait_closed</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.StreamWriter.wait_closed" title="Link to this definition">¶</a></dt>611<dd><p>Wait until the stream is closed.</p>612<p>Should be called after <a class="reference internal" href="#asyncio.StreamWriter.close" title="asyncio.StreamWriter.close"><code class="xref py py-meth docutils literal notranslate"><span class="pre">close()</span></code></a> to wait until the underlying613connection is closed, ensuring that all data has been flushed614before e.g. exiting the program.</p>615<div class="versionadded">616<p><span class="versionmodified added">Added in version 3.7.</span></p>617</div>618</dd></dl>619 620</dd></dl>621 622</section>623<section id="examples">624<h2>Examples<a class="headerlink" href="#examples" title="Link to this heading">¶</a></h2>625<section id="tcp-echo-client-using-streams">626<span id="asyncio-tcp-echo-client-streams"></span><h3>TCP echo client using streams<a class="headerlink" href="#tcp-echo-client-using-streams" title="Link to this heading">¶</a></h3>627<p>TCP echo client using the <a class="reference internal" href="#asyncio.open_connection" title="asyncio.open_connection"><code class="xref py py-func docutils literal notranslate"><span class="pre">asyncio.open_connection()</span></code></a> function:</p>628<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span><span class="w"> </span><span class="nn">asyncio</span>629 630<span class="k">async</span> <span class="k">def</span><span class="w"> </span><span class="nf">tcp_echo_client</span><span class="p">(</span><span class="n">message</span><span class="p">):</span>631    <span class="n">reader</span><span class="p">,</span> <span class="n">writer</span> <span class="o">=</span> <span class="k">await</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">open_connection</span><span class="p">(</span>632        <span class="s1">&#39;127.0.0.1&#39;</span><span class="p">,</span> <span class="mi">8888</span><span class="p">)</span>633 634    <span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s1">&#39;Send: </span><span class="si">{</span><span class="n">message</span><span class="si">!r}</span><span class="s1">&#39;</span><span class="p">)</span>635    <span class="n">writer</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="n">message</span><span class="o">.</span><span class="n">encode</span><span class="p">())</span>636    <span class="k">await</span> <span class="n">writer</span><span class="o">.</span><span class="n">drain</span><span class="p">()</span>637 638    <span class="n">data</span> <span class="o">=</span> <span class="k">await</span> <span class="n">reader</span><span class="o">.</span><span class="n">read</span><span class="p">(</span><span class="mi">100</span><span class="p">)</span>639    <span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s1">&#39;Received: </span><span class="si">{</span><span class="n">data</span><span class="o">.</span><span class="n">decode</span><span class="p">()</span><span class="si">!r}</span><span class="s1">&#39;</span><span class="p">)</span>640 641    <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;Close the connection&#39;</span><span class="p">)</span>642    <span class="n">writer</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>643    <span class="k">await</span> <span class="n">writer</span><span class="o">.</span><span class="n">wait_closed</span><span class="p">()</span>644 645<span class="n">asyncio</span><span class="o">.</span><span class="n">run</span><span class="p">(</span><span class="n">tcp_echo_client</span><span class="p">(</span><span class="s1">&#39;Hello World!&#39;</span><span class="p">))</span>646</pre></div>647</div>648<div class="admonition seealso">649<p class="admonition-title">See also</p>650<p>The <a class="reference internal" href="asyncio-protocol.html#asyncio-example-tcp-echo-client-protocol"><span class="std std-ref">TCP echo client protocol</span></a>651example uses the low-level <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.create_connection" title="asyncio.loop.create_connection"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.create_connection()</span></code></a> method.</p>652</div>653</section>654<section id="tcp-echo-server-using-streams">655<span id="asyncio-tcp-echo-server-streams"></span><h3>TCP echo server using streams<a class="headerlink" href="#tcp-echo-server-using-streams" title="Link to this heading">¶</a></h3>656<p>TCP echo server using the <a class="reference internal" href="#asyncio.start_server" title="asyncio.start_server"><code class="xref py py-func docutils literal notranslate"><span class="pre">asyncio.start_server()</span></code></a> function:</p>657<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span><span class="w"> </span><span class="nn">asyncio</span>658 659<span class="k">async</span> <span class="k">def</span><span class="w"> </span><span class="nf">handle_echo</span><span class="p">(</span><span class="n">reader</span><span class="p">,</span> <span class="n">writer</span><span class="p">):</span>660    <span class="n">data</span> <span class="o">=</span> <span class="k">await</span> <span class="n">reader</span><span class="o">.</span><span class="n">read</span><span class="p">(</span><span class="mi">100</span><span class="p">)</span>661    <span class="n">message</span> <span class="o">=</span> <span class="n">data</span><span class="o">.</span><span class="n">decode</span><span class="p">()</span>662    <span class="n">addr</span> <span class="o">=</span> <span class="n">writer</span><span class="o">.</span><span class="n">get_extra_info</span><span class="p">(</span><span class="s1">&#39;peername&#39;</span><span class="p">)</span>663 664    <span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s2">&quot;Received </span><span class="si">{</span><span class="n">message</span><span class="si">!r}</span><span class="s2"> from </span><span class="si">{</span><span class="n">addr</span><span class="si">!r}</span><span class="s2">&quot;</span><span class="p">)</span>665 666    <span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s2">&quot;Send: </span><span class="si">{</span><span class="n">message</span><span class="si">!r}</span><span class="s2">&quot;</span><span class="p">)</span>667    <span class="n">writer</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="n">data</span><span class="p">)</span>668    <span class="k">await</span> <span class="n">writer</span><span class="o">.</span><span class="n">drain</span><span class="p">()</span>669 670    <span class="nb">print</span><span class="p">(</span><span class="s2">&quot;Close the connection&quot;</span><span class="p">)</span>671    <span class="n">writer</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>672    <span class="k">await</span> <span class="n">writer</span><span class="o">.</span><span class="n">wait_closed</span><span class="p">()</span>673 674<span class="k">async</span> <span class="k">def</span><span class="w"> </span><span class="nf">main</span><span class="p">():</span>675    <span class="n">server</span> <span class="o">=</span> <span class="k">await</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">start_server</span><span class="p">(</span>676        <span class="n">handle_echo</span><span class="p">,</span> <span class="s1">&#39;127.0.0.1&#39;</span><span class="p">,</span> <span class="mi">8888</span><span class="p">)</span>677 678    <span class="n">addrs</span> <span class="o">=</span> <span class="s1">&#39;, &#39;</span><span class="o">.</span><span class="n">join</span><span class="p">(</span><span class="nb">str</span><span class="p">(</span><span class="n">sock</span><span class="o">.</span><span class="n">getsockname</span><span class="p">())</span> <span class="k">for</span> <span class="n">sock</span> <span class="ow">in</span> <span class="n">server</span><span class="o">.</span><span class="n">sockets</span><span class="p">)</span>679    <span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s1">&#39;Serving on </span><span class="si">{</span><span class="n">addrs</span><span class="si">}</span><span class="s1">&#39;</span><span class="p">)</span>680 681    <span class="k">async</span> <span class="k">with</span> <span class="n">server</span><span class="p">:</span>682        <span class="k">await</span> <span class="n">server</span><span class="o">.</span><span class="n">serve_forever</span><span class="p">()</span>683 684<span class="n">asyncio</span><span class="o">.</span><span class="n">run</span><span class="p">(</span><span class="n">main</span><span class="p">())</span>685</pre></div>686</div>687<div class="admonition seealso">688<p class="admonition-title">See also</p>689<p>The <a class="reference internal" href="asyncio-protocol.html#asyncio-example-tcp-echo-server-protocol"><span class="std std-ref">TCP echo server protocol</span></a>690example uses the <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.create_server" title="asyncio.loop.create_server"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.create_server()</span></code></a> method.</p>691</div>692</section>693<section id="get-http-headers">694<h3>Get HTTP headers<a class="headerlink" href="#get-http-headers" title="Link to this heading">¶</a></h3>695<p>Simple example querying HTTP headers of the URL passed on the command line:</p>696<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span><span class="w"> </span><span class="nn">asyncio</span>697<span class="kn">import</span><span class="w"> </span><span class="nn">urllib.parse</span>698<span class="kn">import</span><span class="w"> </span><span class="nn">sys</span>699 700<span class="k">async</span> <span class="k">def</span><span class="w"> </span><span class="nf">print_http_headers</span><span class="p">(</span><span class="n">url</span><span class="p">):</span>701    <span class="n">url</span> <span class="o">=</span> <span class="n">urllib</span><span class="o">.</span><span class="n">parse</span><span class="o">.</span><span class="n">urlsplit</span><span class="p">(</span><span class="n">url</span><span class="p">)</span>702    <span class="k">if</span> <span class="n">url</span><span class="o">.</span><span class="n">scheme</span> <span class="o">==</span> <span class="s1">&#39;https&#39;</span><span class="p">:</span>703        <span class="n">reader</span><span class="p">,</span> <span class="n">writer</span> <span class="o">=</span> <span class="k">await</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">open_connection</span><span class="p">(</span>704            <span class="n">url</span><span class="o">.</span><span class="n">hostname</span><span class="p">,</span> <span class="mi">443</span><span class="p">,</span> <span class="n">ssl</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span>705    <span class="k">else</span><span class="p">:</span>706        <span class="n">reader</span><span class="p">,</span> <span class="n">writer</span> <span class="o">=</span> <span class="k">await</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">open_connection</span><span class="p">(</span>707            <span class="n">url</span><span class="o">.</span><span class="n">hostname</span><span class="p">,</span> <span class="mi">80</span><span class="p">)</span>708 709    <span class="n">query</span> <span class="o">=</span> <span class="p">(</span>710        <span class="sa">f</span><span class="s2">&quot;HEAD </span><span class="si">{</span><span class="n">url</span><span class="o">.</span><span class="n">path</span><span class="w"> </span><span class="ow">or</span><span class="w"> </span><span class="s1">&#39;/&#39;</span><span class="si">}</span><span class="s2"> HTTP/1.0</span><span class="se">\r\n</span><span class="s2">&quot;</span>711        <span class="sa">f</span><span class="s2">&quot;Host: </span><span class="si">{</span><span class="n">url</span><span class="o">.</span><span class="n">hostname</span><span class="si">}</span><span class="se">\r\n</span><span class="s2">&quot;</span>712        <span class="sa">f</span><span class="s2">&quot;</span><span class="se">\r\n</span><span class="s2">&quot;</span>713    <span class="p">)</span>714 715    <span class="n">writer</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="n">query</span><span class="o">.</span><span class="n">encode</span><span class="p">(</span><span class="s1">&#39;latin-1&#39;</span><span class="p">))</span>716    <span class="k">while</span> <span class="kc">True</span><span class="p">:</span>717        <span class="n">line</span> <span class="o">=</span> <span class="k">await</span> <span class="n">reader</span><span class="o">.</span><span class="n">readline</span><span class="p">()</span>718        <span class="k">if</span> <span class="ow">not</span> <span class="n">line</span><span class="p">:</span>719            <span class="k">break</span>720 721        <span class="n">line</span> <span class="o">=</span> <span class="n">line</span><span class="o">.</span><span class="n">decode</span><span class="p">(</span><span class="s1">&#39;latin1&#39;</span><span class="p">)</span><span class="o">.</span><span class="n">rstrip</span><span class="p">()</span>722        <span class="k">if</span> <span class="n">line</span><span class="p">:</span>723            <span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s1">&#39;HTTP header&gt; </span><span class="si">{</span><span class="n">line</span><span class="si">}</span><span class="s1">&#39;</span><span class="p">)</span>724 725    <span class="c1"># Ignore the body, close the socket</span>726    <span class="n">writer</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>727    <span class="k">await</span> <span class="n">writer</span><span class="o">.</span><span class="n">wait_closed</span><span class="p">()</span>728 729<span class="n">url</span> <span class="o">=</span> <span class="n">sys</span><span class="o">.</span><span class="n">argv</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span>730<span class="n">asyncio</span><span class="o">.</span><span class="n">run</span><span class="p">(</span><span class="n">print_http_headers</span><span class="p">(</span><span class="n">url</span><span class="p">))</span>731</pre></div>732</div>733<p>Usage:</p>734<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">python</span> <span class="n">example</span><span class="o">.</span><span class="n">py</span> <span class="n">http</span><span class="p">:</span><span class="o">//</span><span class="n">example</span><span class="o">.</span><span class="n">com</span><span class="o">/</span><span class="n">path</span><span class="o">/</span><span class="n">page</span><span class="o">.</span><span class="n">html</span>735</pre></div>736</div>737<p>or with HTTPS:</p>738<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">python</span> <span class="n">example</span><span class="o">.</span><span class="n">py</span> <span class="n">https</span><span class="p">:</span><span class="o">//</span><span class="n">example</span><span class="o">.</span><span class="n">com</span><span class="o">/</span><span class="n">path</span><span class="o">/</span><span class="n">page</span><span class="o">.</span><span class="n">html</span>739</pre></div>740</div>741</section>742<section id="register-an-open-socket-to-wait-for-data-using-streams">743<span id="asyncio-example-create-connection-streams"></span><h3>Register an open socket to wait for data using streams<a class="headerlink" href="#register-an-open-socket-to-wait-for-data-using-streams" title="Link to this heading">¶</a></h3>744<p>Coroutine waiting until a socket receives data using the745<a class="reference internal" href="#asyncio.open_connection" title="asyncio.open_connection"><code class="xref py py-func docutils literal notranslate"><span class="pre">open_connection()</span></code></a> function:</p>746<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span><span class="w"> </span><span class="nn">asyncio</span>747<span class="kn">import</span><span class="w"> </span><span class="nn">socket</span>748 749<span class="k">async</span> <span class="k">def</span><span class="w"> </span><span class="nf">wait_for_data</span><span class="p">():</span>750    <span class="c1"># Get a reference to the current event loop because</span>751    <span class="c1"># we want to access low-level APIs.</span>752    <span class="n">loop</span> <span class="o">=</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">get_running_loop</span><span class="p">()</span>753 754    <span class="c1"># Create a pair of connected sockets.</span>755    <span class="n">rsock</span><span class="p">,</span> <span class="n">wsock</span> <span class="o">=</span> <span class="n">socket</span><span class="o">.</span><span class="n">socketpair</span><span class="p">()</span>756 757    <span class="c1"># Register the open socket to wait for data.</span>758    <span class="n">reader</span><span class="p">,</span> <span class="n">writer</span> <span class="o">=</span> <span class="k">await</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">open_connection</span><span class="p">(</span><span class="n">sock</span><span class="o">=</span><span class="n">rsock</span><span class="p">)</span>759 760    <span class="c1"># Simulate the reception of data from the network</span>761    <span class="n">loop</span><span class="o">.</span><span class="n">call_soon</span><span class="p">(</span><span class="n">wsock</span><span class="o">.</span><span class="n">send</span><span class="p">,</span> <span class="s1">&#39;abc&#39;</span><span class="o">.</span><span class="n">encode</span><span class="p">())</span>762 763    <span class="c1"># Wait for data</span>764    <span class="n">data</span> <span class="o">=</span> <span class="k">await</span> <span class="n">reader</span><span class="o">.</span><span class="n">read</span><span class="p">(</span><span class="mi">100</span><span class="p">)</span>765 766    <span class="c1"># Got data, we are done: close the socket</span>767    <span class="nb">print</span><span class="p">(</span><span class="s2">&quot;Received:&quot;</span><span class="p">,</span> <span class="n">data</span><span class="o">.</span><span class="n">decode</span><span class="p">())</span>768    <span class="n">writer</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>769    <span class="k">await</span> <span class="n">writer</span><span class="o">.</span><span class="n">wait_closed</span><span class="p">()</span>770 771    <span class="c1"># Close the second socket</span>772    <span class="n">wsock</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>773 774<span class="n">asyncio</span><span class="o">.</span><span class="n">run</span><span class="p">(</span><span class="n">wait_for_data</span><span class="p">())</span>775</pre></div>776</div>777<div class="admonition seealso">778<p class="admonition-title">See also</p>779<p>The <a class="reference internal" href="asyncio-protocol.html#asyncio-example-create-connection"><span class="std std-ref">register an open socket to wait for data using a protocol</span></a> example uses a low-level protocol and780the <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.create_connection" title="asyncio.loop.create_connection"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.create_connection()</span></code></a> method.</p>781<p>The <a class="reference internal" href="asyncio-eventloop.html#asyncio-example-watch-fd"><span class="std std-ref">watch a file descriptor for read events</span></a> example uses the low-level782<a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.add_reader" title="asyncio.loop.add_reader"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.add_reader()</span></code></a> method to watch a file descriptor.</p>783</div>784</section>785</section>786</section>787 788 789            <div class="clearer"></div>790          </div>791        </div>792      </div>793      <div class="sphinxsidebar" role="navigation" aria-label="Main">794        <div class="sphinxsidebarwrapper">795  <div>796    <h3><a href="../contents.html">Table of Contents</a></h3>797    <ul>798<li><a class="reference internal" href="#">Streams</a><ul>799<li><a class="reference internal" href="#streamreader">StreamReader</a></li>800<li><a class="reference internal" href="#streamwriter">StreamWriter</a></li>801<li><a class="reference internal" href="#examples">Examples</a><ul>802<li><a class="reference internal" href="#tcp-echo-client-using-streams">TCP echo client using streams</a></li>803<li><a class="reference internal" href="#tcp-echo-server-using-streams">TCP echo server using streams</a></li>804<li><a class="reference internal" href="#get-http-headers">Get HTTP headers</a></li>805<li><a class="reference internal" href="#register-an-open-socket-to-wait-for-data-using-streams">Register an open socket to wait for data using streams</a></li>806</ul>807</li>808</ul>809</li>810</ul>811 812  </div>813  <div>814    <h4>Previous topic</h4>815    <p class="topless"><a href="asyncio-task.html"816                          title="previous chapter">Coroutines and Tasks</a></p>817  </div>818  <div>819    <h4>Next topic</h4>820    <p class="topless"><a href="asyncio-sync.html"821                          title="next chapter">Synchronization Primitives</a></p>822  </div>823  <script>824    document.addEventListener('DOMContentLoaded', () => {825        const title = document.querySelector('meta[property="og:title"]').content;826        const elements = 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