<!DOCTYPE html> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta charset="utf-8" /> <title>asyncio — Asynchronous I/O — Python 3.7.10 documentation</title> <link rel="stylesheet" href="../_static/pydoctheme.css" type="text/css" /> <link rel="stylesheet" href="../_static/pygments.css" type="text/css" /> <script type="text/javascript" id="documentation_options" data-url_root="../" src="../_static/documentation_options.js"></script> <script type="text/javascript" src="../_static/jquery.js"></script> <script type="text/javascript" src="../_static/underscore.js"></script> <script type="text/javascript" src="../_static/doctools.js"></script> <script type="text/javascript" src="../_static/language_data.js"></script> <script type="text/javascript" src="../_static/sidebar.js"></script> <link rel="search" type="application/opensearchdescription+xml" title="Search within Python 3.7.10 documentation" href="../_static/opensearch.xml"/> <link rel="author" title="About these documents" href="../about.html" /> <link rel="index" title="Index" href="../genindex.html" /> <link rel="search" title="Search" href="../search.html" /> <link rel="copyright" title="Copyright" href="../copyright.html" /> <link rel="next" title="Coroutines and Tasks" href="asyncio-task.html" /> <link rel="prev" title="Networking and Interprocess Communication" href="ipc.html" /> <link rel="shortcut icon" type="image/png" href="../_static/py.png" /> <link rel="canonical" href="https://docs.python.org/3/library/asyncio.html" /> <script type="text/javascript" src="../_static/copybutton.js"></script> <style> @media only screen { table.full-width-table { width: 100%; } } </style> </head><body> <div class="related" role="navigation" aria-label="related navigation"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="../genindex.html" title="General Index" accesskey="I">index</a></li> <li class="right" > <a href="../py-modindex.html" title="Python Module Index" >modules</a> |</li> <li class="right" > <a href="asyncio-task.html" title="Coroutines and Tasks" accesskey="N">next</a> |</li> <li class="right" > <a href="ipc.html" title="Networking and Interprocess Communication" accesskey="P">previous</a> |</li> <li><img src="../_static/py.png" alt="" style="vertical-align: middle; margin-top: -1px"/></li> <li><a href="https://www.python.org/">Python</a> »</li> <li> <a href="../index.html">3.7.10 Documentation</a> » </li> <li class="nav-item nav-item-1"><a href="index.html" >The Python Standard Library</a> »</li> <li class="nav-item nav-item-2"><a href="ipc.html" accesskey="U">Networking and Interprocess Communication</a> »</li> <li class="right"> <div class="inline-search" style="display: none" role="search"> <form class="inline-search" action="../search.html" method="get"> <input placeholder="Quick search" type="text" name="q" /> <input type="submit" value="Go" /> <input type="hidden" name="check_keywords" value="yes" /> <input type="hidden" name="area" value="default" /> </form> </div> <script type="text/javascript">$('.inline-search').show(0);</script> | </li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body" role="main"> <div class="section" id="module-asyncio"> <span id="asyncio-asynchronous-i-o"></span><h1><a class="reference internal" href="#module-asyncio" title="asyncio: Asynchronous I/O."><code class="xref py py-mod docutils literal notranslate"><span class="pre">asyncio</span></code></a> — Asynchronous I/O<a class="headerlink" href="#module-asyncio" title="Permalink to this headline">¶</a></h1> <hr class="docutils" /> <div class="sidebar"> <p class="sidebar-title">Hello World!</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">asyncio</span> <span class="k">async</span> <span class="k">def</span> <span class="nf">main</span><span class="p">():</span> <span class="nb">print</span><span class="p">(</span><span class="s1">'Hello ...'</span><span class="p">)</span> <span class="k">await</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">sleep</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span> <span class="nb">print</span><span class="p">(</span><span class="s1">'... World!'</span><span class="p">)</span> <span class="c1"># Python 3.7+</span> <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> </pre></div> </div> </div> <p>asyncio is a library to write <strong>concurrent</strong> code using the <strong>async/await</strong> syntax.</p> <p>asyncio is used as a foundation for multiple Python asynchronous frameworks that provide high-performance network and web-servers, database connection libraries, distributed task queues, etc.</p> <p>asyncio is often a perfect fit for IO-bound and high-level <strong>structured</strong> network code.</p> <p>asyncio provides a set of <strong>high-level</strong> APIs to:</p> <ul class="simple"> <li><p><a class="reference internal" href="asyncio-task.html#coroutine"><span class="std std-ref">run Python coroutines</span></a> concurrently and have full control over their execution;</p></li> <li><p>perform <a class="reference internal" href="asyncio-stream.html#asyncio-streams"><span class="std std-ref">network IO and IPC</span></a>;</p></li> <li><p>control <a class="reference internal" href="asyncio-subprocess.html#asyncio-subprocess"><span class="std std-ref">subprocesses</span></a>;</p></li> <li><p>distribute tasks via <a class="reference internal" href="asyncio-queue.html#asyncio-queues"><span class="std std-ref">queues</span></a>;</p></li> <li><p><a class="reference internal" href="asyncio-sync.html#asyncio-sync"><span class="std std-ref">synchronize</span></a> concurrent code;</p></li> </ul> <p>Additionally, there are <strong>low-level</strong> APIs for <em>library and framework developers</em> to:</p> <ul class="simple"> <li><p>create and manage <a class="reference internal" href="asyncio-eventloop.html#asyncio-event-loop"><span class="std std-ref">event loops</span></a>, which provide asynchronous APIs for <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">networking</span></code></a>, running <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.subprocess_exec" title="asyncio.loop.subprocess_exec"><code class="xref py py-meth docutils literal notranslate"><span class="pre">subprocesses</span></code></a>, handling <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.add_signal_handler" title="asyncio.loop.add_signal_handler"><code class="xref py py-meth docutils literal notranslate"><span class="pre">OS</span> <span class="pre">signals</span></code></a>, etc;</p></li> <li><p>implement efficient protocols using <a class="reference internal" href="asyncio-protocol.html#asyncio-transports-protocols"><span class="std std-ref">transports</span></a>;</p></li> <li><p><a class="reference internal" href="asyncio-future.html#asyncio-futures"><span class="std std-ref">bridge</span></a> callback-based libraries and code with async/await syntax.</p></li> </ul> <p class="rubric">Reference</p> <div class="toctree-wrapper compound"> <p class="caption"><span class="caption-text">High-level APIs</span></p> <ul> <li class="toctree-l1"><a class="reference internal" href="asyncio-task.html">Coroutines and Tasks</a></li> <li class="toctree-l1"><a class="reference internal" href="asyncio-stream.html">Streams</a></li> <li class="toctree-l1"><a class="reference internal" href="asyncio-sync.html">Synchronization Primitives</a></li> <li class="toctree-l1"><a class="reference internal" href="asyncio-subprocess.html">Subprocesses</a></li> <li class="toctree-l1"><a class="reference internal" href="asyncio-queue.html">Queues</a></li> <li class="toctree-l1"><a class="reference internal" href="asyncio-exceptions.html">Exceptions</a></li> </ul> </div> <div class="toctree-wrapper compound"> <p class="caption"><span class="caption-text">Low-level APIs</span></p> <ul> <li class="toctree-l1"><a class="reference internal" href="asyncio-eventloop.html">Event Loop</a></li> <li class="toctree-l1"><a class="reference internal" href="asyncio-future.html">Futures</a></li> <li class="toctree-l1"><a class="reference internal" href="asyncio-protocol.html">Transports and Protocols</a></li> <li class="toctree-l1"><a class="reference internal" href="asyncio-policy.html">Policies</a></li> <li class="toctree-l1"><a class="reference internal" href="asyncio-platforms.html">Platform Support</a></li> </ul> </div> <div class="toctree-wrapper compound"> <p class="caption"><span class="caption-text">Guides and Tutorials</span></p> <ul> <li class="toctree-l1"><a class="reference internal" href="asyncio-api-index.html">High-level API Index</a></li> <li class="toctree-l1"><a class="reference internal" href="asyncio-llapi-index.html">Low-level API Index</a></li> <li class="toctree-l1"><a 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