Spaces:
Sleeping
Sleeping
| <html lang="en" data-content_root="../"> | |
| <head> | |
| <meta charset="utf-8" /> | |
| <meta name="viewport" content="width=device-width, initial-scale=1.0" /><meta name="viewport" content="width=device-width, initial-scale=1" /> | |
| <meta property="og:title" content="Futures" /> | |
| <meta property="og:type" content="website" /> | |
| <meta property="og:url" content="https://docs.python.org/3/library/asyncio-future.html" /> | |
| <meta property="og:site_name" content="Python documentation" /> | |
| <meta property="og:description" content="Source code: Lib/asyncio/futures.py, Lib/asyncio/base_futures.py Future objects are used to bridge low-level callback-based code with high-level async/await code. Future Functions: Future Object: T..." /> | |
| <meta property="og:image:width" content="1146" /> | |
| <meta property="og:image:height" content="600" /> | |
| <meta property="og:image" content="https://docs.python.org/3.15/_images/social_previews/summary_library_asyncio-future_bb00f916.png" /> | |
| <meta property="og:image:alt" content="Source code: Lib/asyncio/futures.py, Lib/asyncio/base_futures.py Future objects are used to bridge low-level callback-based code with high-level async/await code. Future Functions: Future Object: T..." /> | |
| <meta name="description" content="Source code: Lib/asyncio/futures.py, Lib/asyncio/base_futures.py Future objects are used to bridge low-level callback-based code with high-level async/await code. Future Functions: Future Object: T..." /> | |
| <meta name="twitter:card" content="summary_large_image" /> | |
| <meta name="theme-color" content="#3776ab"> | |
| <title>Futures — Python 3.15.0a6 documentation</title><meta name="viewport" content="width=device-width, initial-scale=1.0"> | |
| <link rel="stylesheet" type="text/css" href="../_static/pygments.css?v=b86133f3" /> | |
| <link rel="stylesheet" type="text/css" href="../_static/classic.css?v=234b1a7c" /> | |
| <link rel="stylesheet" type="text/css" href="../_static/pydoctheme.css?v=89a2f22a" /> | |
| <link rel="stylesheet" type="text/css" href="../_static/profiling-sampling-visualization.css?v=0c2600ae" /> | |
| <link id="pygments_dark_css" media="(prefers-color-scheme: dark)" rel="stylesheet" type="text/css" href="../_static/pygments_dark.css?v=5349f25f" /> | |
| <script src="../_static/documentation_options.js?v=6b7c9ff5"></script> | |
| <script src="../_static/doctools.js?v=9bcbadda"></script> | |
| <script src="../_static/sphinx_highlight.js?v=dc90522c"></script> | |
| <script src="../_static/profiling-sampling-visualization.js?v=9811ed04"></script> | |
| <script src="../_static/sidebar.js"></script> | |
| <link rel="search" type="application/opensearchdescription+xml" | |
| title="Search within Python 3.15.0a6 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="Transports and Protocols" href="asyncio-protocol.html" /> | |
| <link rel="prev" title="Event Loop" href="asyncio-eventloop.html" /> | |
| <script defer file-types="bz2,epub,zip" data-domain="docs.python.org" src="https://analytics.python.org/js/script.file-downloads.outbound-links.js"></script> | |
| <link rel="canonical" href="https://docs.python.org/3/library/asyncio-future.html"> | |
| <style> | |
| @media only screen { | |
| table.full-width-table { | |
| width: 100%; | |
| } | |
| } | |
| </style> | |
| <link rel="stylesheet" href="../_static/pydoctheme_dark.css" media="(prefers-color-scheme: dark)" id="pydoctheme_dark_css"> | |
| <link rel="shortcut icon" type="image/png" href="../_static/py.svg"> | |
| <script type="text/javascript" src="../_static/copybutton.js"></script> | |
| <script type="text/javascript" src="../_static/menu.js"></script> | |
| <script type="text/javascript" src="../_static/search-focus.js"></script> | |
| <script type="text/javascript" src="../_static/themetoggle.js"></script> | |
| <script type="text/javascript" src="../_static/rtd_switcher.js"></script> | |
| <meta name="readthedocs-addons-api-version" content="1"> | |
| </head> | |
| <body> | |
| <div class="mobile-nav"> | |
| <input type="checkbox" id="menuToggler" class="toggler__input" aria-controls="navigation" | |
| aria-pressed="false" aria-expanded="false" role="button" aria-label="Menu"> | |
| <nav class="nav-content" role="navigation"> | |
| <label for="menuToggler" class="toggler__label"> | |
| <span></span> | |
| </label> | |
| <span class="nav-items-wrapper"> | |
| <a href="https://www.python.org/" class="nav-logo"> | |
| <img src="../_static/py.svg" alt="Python logo"> | |
| </a> | |
| <span class="version_switcher_placeholder"></span> | |
| <form role="search" class="search" action="../search.html" method="get"> | |
| <svg xmlns="http://www.w3.org/2000/svg" width="20" height="20" viewBox="0 0 24 24" class="search-icon"> | |
| <path fill-rule="nonzero" fill="currentColor" d="M15.5 14h-.79l-.28-.27a6.5 6.5 0 001.48-5.34c-.47-2.78-2.79-5-5.59-5.34a6.505 6.505 0 00-7.27 7.27c.34 2.8 2.56 5.12 5.34 5.59a6.5 6.5 0 005.34-1.48l.27.28v.79l4.25 4.25c.41.41 1.08.41 1.49 0 .41-.41.41-1.08 0-1.49L15.5 14zm-6 0C7.01 14 5 11.99 5 9.5S7.01 5 9.5 5 14 7.01 14 9.5 11.99 14 9.5 14z"></path> | |
| </svg> | |
| <input placeholder="Quick search" aria-label="Quick search" type="search" name="q"> | |
| <input type="submit" value="Go"> | |
| </form> | |
| </span> | |
| </nav> | |
| <div class="menu-wrapper"> | |
| <nav class="menu" role="navigation" aria-label="main navigation"> | |
| <div class="language_switcher_placeholder"></div> | |
| <label class="theme-selector-label"> | |
| Theme | |
| <select class="theme-selector" oninput="activateTheme(this.value)"> | |
| <option value="auto" selected>Auto</option> | |
| <option value="light">Light</option> | |
| <option value="dark">Dark</option> | |
| </select> | |
| </label> | |
| <div> | |
| <h3><a href="../contents.html">Table of Contents</a></h3> | |
| <ul> | |
| <li><a class="reference internal" href="#">Futures</a><ul> | |
| <li><a class="reference internal" href="#future-functions">Future Functions</a></li> | |
| <li><a class="reference internal" href="#future-object">Future Object</a></li> | |
| </ul> | |
| </li> | |
| </ul> | |
| </div> | |
| <div> | |
| <h4>Previous topic</h4> | |
| <p class="topless"><a href="asyncio-eventloop.html" | |
| title="previous chapter">Event Loop</a></p> | |
| </div> | |
| <div> | |
| <h4>Next topic</h4> | |
| <p class="topless"><a href="asyncio-protocol.html" | |
| title="next chapter">Transports and Protocols</a></p> | |
| </div> | |
| <script> | |
| document.addEventListener('DOMContentLoaded', () => { | |
| const title = document.querySelector('meta[property="og:title"]').content; | |
| const elements = document.querySelectorAll('.improvepage'); | |
| const pageurl = window.location.href.split('?')[0]; | |
| elements.forEach(element => { | |
| const url = new URL(element.href.split('?')[0].replace("-nojs", "")); | |
| url.searchParams.set('pagetitle', title); | |
| url.searchParams.set('pageurl', pageurl); | |
| url.searchParams.set('pagesource', "library/asyncio-future.rst"); | |
| element.href = url.toString(); | |
| }); | |
| }); | |
| </script> | |
| <div role="note" aria-label="source link"> | |
| <h3>This page</h3> | |
| <ul class="this-page-menu"> | |
| <li><a href="../bugs.html">Report a bug</a></li> | |
| <li><a class="improvepage" href="../improve-page-nojs.html">Improve this page</a></li> | |
| <li> | |
| <a href="https://github.com/python/cpython/blob/main/Doc/library/asyncio-future.rst?plain=1" | |
| rel="nofollow">Show source | |
| </a> | |
| </li> | |
| </ul> | |
| </div> | |
| </nav> | |
| </div> | |
| </div> | |
| <div class="related" role="navigation" aria-label="Related"> | |
| <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-protocol.html" title="Transports and Protocols" | |
| accesskey="N">next</a> |</li> | |
| <li class="right" > | |
| <a href="asyncio-eventloop.html" title="Event Loop" | |
| accesskey="P">previous</a> |</li> | |
| <li><img src="../_static/py.svg" alt="Python logo" style="vertical-align: middle; margin-top: -1px"></li> | |
| <li><a href="https://www.python.org/">Python</a> »</li> | |
| <li class="switchers"> | |
| <div class="language_switcher_placeholder"></div> | |
| <div class="version_switcher_placeholder"></div> | |
| </li> | |
| <li> | |
| </li> | |
| <li id="cpython-language-and-version"> | |
| <a href="../index.html">3.15.0a6 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" >Networking and Interprocess Communication</a> »</li> | |
| <li class="nav-item 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> »</li> | |
| <li class="nav-item nav-item-this"><a href="">Futures</a></li> | |
| <li class="right"> | |
| <div class="inline-search" role="search"> | |
| <form class="inline-search" action="../search.html" method="get"> | |
| <input placeholder="Quick search" aria-label="Quick search" type="search" name="q" id="search-box"> | |
| <input type="submit" value="Go"> | |
| </form> | |
| </div> | |
| | | |
| </li> | |
| <li class="right"> | |
| <label class="theme-selector-label"> | |
| Theme | |
| <select class="theme-selector" oninput="activateTheme(this.value)"> | |
| <option value="auto" selected>Auto</option> | |
| <option value="light">Light</option> | |
| <option value="dark">Dark</option> | |
| </select> | |
| </label> |</li> | |
| </ul> | |
| </div> | |
| <div class="document"> | |
| <div class="documentwrapper"> | |
| <div class="bodywrapper"> | |
| <div class="body" role="main"> | |
| <section id="futures"> | |
| <span id="asyncio-futures"></span><h1>Futures<a class="headerlink" href="#futures" title="Link to this heading">¶</a></h1> | |
| <p><strong>Source code:</strong> <a class="extlink-source reference external" href="https://github.com/python/cpython/tree/main/Lib/asyncio/futures.py">Lib/asyncio/futures.py</a>, | |
| <a class="extlink-source reference external" href="https://github.com/python/cpython/tree/main/Lib/asyncio/base_futures.py">Lib/asyncio/base_futures.py</a></p> | |
| <hr class="docutils" /> | |
| <p><em>Future</em> objects are used to bridge <strong>low-level callback-based code</strong> | |
| with high-level async/await code.</p> | |
| <section id="future-functions"> | |
| <h2>Future Functions<a class="headerlink" href="#future-functions" title="Link to this heading">¶</a></h2> | |
| <dl class="py function"> | |
| <dt class="sig sig-object py" id="asyncio.isfuture"> | |
| <span class="sig-prename descclassname"><span class="pre">asyncio.</span></span><span class="sig-name descname"><span class="pre">isfuture</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">obj</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.isfuture" title="Link to this definition">¶</a></dt> | |
| <dd><p>Return <code class="docutils literal notranslate"><span class="pre">True</span></code> if <em>obj</em> is either of:</p> | |
| <ul class="simple"> | |
| <li><p>an instance of <a class="reference internal" href="#asyncio.Future" title="asyncio.Future"><code class="xref py py-class docutils literal notranslate"><span class="pre">asyncio.Future</span></code></a>,</p></li> | |
| <li><p>an instance of <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">asyncio.Task</span></code></a>,</p></li> | |
| <li><p>a Future-like object with a <code class="docutils literal notranslate"><span class="pre">_asyncio_future_blocking</span></code> | |
| attribute.</p></li> | |
| </ul> | |
| <div class="versionadded"> | |
| <p><span class="versionmodified added">Added in version 3.5.</span></p> | |
| </div> | |
| </dd></dl> | |
| <dl class="py function"> | |
| <dt class="sig sig-object py" id="asyncio.ensure_future"> | |
| <span class="sig-prename descclassname"><span class="pre">asyncio.</span></span><span class="sig-name descname"><span class="pre">ensure_future</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="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">loop</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.ensure_future" title="Link to this definition">¶</a></dt> | |
| <dd><p>Return:</p> | |
| <ul class="simple"> | |
| <li><p><em>obj</em> argument as is, if <em>obj</em> is a <a class="reference internal" href="#asyncio.Future" title="asyncio.Future"><code class="xref py py-class docutils literal notranslate"><span class="pre">Future</span></code></a>, | |
| 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>, or a Future-like object (<a class="reference internal" href="#asyncio.isfuture" title="asyncio.isfuture"><code class="xref py py-func docutils literal notranslate"><span class="pre">isfuture()</span></code></a> | |
| is used for the test.)</p></li> | |
| <li><p>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> object wrapping <em>obj</em>, if <em>obj</em> is a | |
| coroutine (<a class="reference internal" href="asyncio-task.html#asyncio.iscoroutine" title="asyncio.iscoroutine"><code class="xref py py-func docutils literal notranslate"><span class="pre">iscoroutine()</span></code></a> is used for the test); | |
| in this case the coroutine will be scheduled by | |
| <code class="docutils literal notranslate"><span class="pre">ensure_future()</span></code>.</p></li> | |
| <li><p>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> object that would await on <em>obj</em>, if <em>obj</em> is an | |
| awaitable (<a class="reference internal" href="inspect.html#inspect.isawaitable" title="inspect.isawaitable"><code class="xref py py-func docutils literal notranslate"><span class="pre">inspect.isawaitable()</span></code></a> is used for the test.)</p></li> | |
| </ul> | |
| <p>If <em>obj</em> is neither of the above a <a class="reference internal" href="exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a> is raised.</p> | |
| <div class="admonition important"> | |
| <p class="admonition-title">Important</p> | |
| <p>Save a reference to the result of this function, to avoid | |
| a task disappearing mid-execution.</p> | |
| <p>See also the <a class="reference internal" href="asyncio-task.html#asyncio.create_task" title="asyncio.create_task"><code class="xref py py-func docutils literal notranslate"><span class="pre">create_task()</span></code></a> function which is the | |
| preferred way for creating new tasks or use <a class="reference internal" href="asyncio-task.html#asyncio.TaskGroup" title="asyncio.TaskGroup"><code class="xref py py-class docutils literal notranslate"><span class="pre">asyncio.TaskGroup</span></code></a> | |
| which keeps reference to the task internally.</p> | |
| </div> | |
| <div class="versionchanged"> | |
| <p><span class="versionmodified changed">Changed in version 3.5.1: </span>The function accepts any <a class="reference internal" href="../glossary.html#term-awaitable"><span class="xref std std-term">awaitable</span></a> object.</p> | |
| </div> | |
| <div class="deprecated"> | |
| <p><span class="versionmodified deprecated">Deprecated since version 3.10: </span>Deprecation warning is emitted if <em>obj</em> is not a Future-like object | |
| and <em>loop</em> is not specified and there is no running event loop.</p> | |
| </div> | |
| </dd></dl> | |
| <dl class="py function"> | |
| <dt class="sig sig-object py" id="asyncio.wrap_future"> | |
| <span class="sig-prename descclassname"><span class="pre">asyncio.</span></span><span class="sig-name descname"><span class="pre">wrap_future</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">future</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">loop</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.wrap_future" title="Link to this definition">¶</a></dt> | |
| <dd><p>Wrap a <a class="reference internal" href="concurrent.futures.html#concurrent.futures.Future" title="concurrent.futures.Future"><code class="xref py py-class docutils literal notranslate"><span class="pre">concurrent.futures.Future</span></code></a> object in a | |
| <a class="reference internal" href="#asyncio.Future" title="asyncio.Future"><code class="xref py py-class docutils literal notranslate"><span class="pre">asyncio.Future</span></code></a> object.</p> | |
| <div class="deprecated"> | |
| <p><span class="versionmodified deprecated">Deprecated since version 3.10: </span>Deprecation warning is emitted if <em>future</em> is not a Future-like object | |
| and <em>loop</em> is not specified and there is no running event loop.</p> | |
| </div> | |
| </dd></dl> | |
| </section> | |
| <section id="future-object"> | |
| <span id="asyncio-future-obj"></span><h2>Future Object<a class="headerlink" href="#future-object" title="Link to this heading">¶</a></h2> | |
| <dl class="py class"> | |
| <dt class="sig sig-object py" id="asyncio.Future"> | |
| <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">Future</span></span><span class="sig-paren">(</span><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">loop</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.Future" title="Link to this definition">¶</a></dt> | |
| <dd><p>A Future represents an eventual result of an asynchronous | |
| operation. Not thread-safe.</p> | |
| <p>Future is an <a class="reference internal" href="../glossary.html#term-awaitable"><span class="xref std std-term">awaitable</span></a> object. Coroutines can await on | |
| Future objects until they either have a result or an exception | |
| set, or until they are cancelled. A Future can be awaited multiple | |
| times and the result is same.</p> | |
| <p>Typically Futures are used to enable low-level | |
| callback-based code (e.g. in protocols implemented using asyncio | |
| <a class="reference internal" href="asyncio-protocol.html#asyncio-transports-protocols"><span class="std std-ref">transports</span></a>) | |
| to interoperate with high-level async/await code.</p> | |
| <p>The rule of thumb is to never expose Future objects in user-facing | |
| APIs, and the recommended way to create a Future object is to call | |
| <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.create_future" title="asyncio.loop.create_future"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.create_future()</span></code></a>. This way alternative event loop | |
| implementations can inject their own optimized implementations | |
| of a Future object.</p> | |
| <div class="versionchanged"> | |
| <p><span class="versionmodified changed">Changed in version 3.7: </span>Added support for the <a class="reference internal" href="contextvars.html#module-contextvars" title="contextvars: Context Variables"><code class="xref py py-mod docutils literal notranslate"><span class="pre">contextvars</span></code></a> module.</p> | |
| </div> | |
| <div class="deprecated"> | |
| <p><span class="versionmodified deprecated">Deprecated since version 3.10: </span>Deprecation warning is emitted if <em>loop</em> is not specified | |
| and there is no running event loop.</p> | |
| </div> | |
| <dl class="py method"> | |
| <dt class="sig sig-object py" id="asyncio.Future.result"> | |
| <span class="sig-name descname"><span class="pre">result</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Future.result" title="Link to this definition">¶</a></dt> | |
| <dd><p>Return the result of the Future.</p> | |
| <p>If the Future is <em>done</em> and has a result set by the | |
| <a class="reference internal" href="#asyncio.Future.set_result" title="asyncio.Future.set_result"><code class="xref py py-meth docutils literal notranslate"><span class="pre">set_result()</span></code></a> method, the result value is returned.</p> | |
| <p>If the Future is <em>done</em> and has an exception set by the | |
| <a class="reference internal" href="#asyncio.Future.set_exception" title="asyncio.Future.set_exception"><code class="xref py py-meth docutils literal notranslate"><span class="pre">set_exception()</span></code></a> method, this method raises the exception.</p> | |
| <p>If the Future has been <em>cancelled</em>, this method raises | |
| a <a class="reference internal" href="asyncio-exceptions.html#asyncio.CancelledError" title="asyncio.CancelledError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">CancelledError</span></code></a> exception.</p> | |
| <p>If the Future’s result isn’t yet available, this method raises | |
| an <a class="reference internal" href="asyncio-exceptions.html#asyncio.InvalidStateError" title="asyncio.InvalidStateError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">InvalidStateError</span></code></a> exception.</p> | |
| </dd></dl> | |
| <dl class="py method"> | |
| <dt class="sig sig-object py" id="asyncio.Future.set_result"> | |
| <span class="sig-name descname"><span class="pre">set_result</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">result</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Future.set_result" title="Link to this definition">¶</a></dt> | |
| <dd><p>Mark the Future as <em>done</em> and set its result.</p> | |
| <p>Raises an <a class="reference internal" href="asyncio-exceptions.html#asyncio.InvalidStateError" title="asyncio.InvalidStateError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">InvalidStateError</span></code></a> error if the Future is | |
| already <em>done</em>.</p> | |
| </dd></dl> | |
| <dl class="py method"> | |
| <dt class="sig sig-object py" id="asyncio.Future.set_exception"> | |
| <span class="sig-name descname"><span class="pre">set_exception</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">exception</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Future.set_exception" title="Link to this definition">¶</a></dt> | |
| <dd><p>Mark the Future as <em>done</em> and set an exception.</p> | |
| <p>Raises an <a class="reference internal" href="asyncio-exceptions.html#asyncio.InvalidStateError" title="asyncio.InvalidStateError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">InvalidStateError</span></code></a> error if the Future is | |
| already <em>done</em>.</p> | |
| </dd></dl> | |
| <dl class="py method"> | |
| <dt class="sig sig-object py" id="asyncio.Future.done"> | |
| <span class="sig-name descname"><span class="pre">done</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Future.done" title="Link to this definition">¶</a></dt> | |
| <dd><p>Return <code class="docutils literal notranslate"><span class="pre">True</span></code> if the Future is <em>done</em>.</p> | |
| <p>A Future is <em>done</em> if it was <em>cancelled</em> or if it has a result | |
| or an exception set with <a class="reference internal" href="#asyncio.Future.set_result" title="asyncio.Future.set_result"><code class="xref py py-meth docutils literal notranslate"><span class="pre">set_result()</span></code></a> or | |
| <a class="reference internal" href="#asyncio.Future.set_exception" title="asyncio.Future.set_exception"><code class="xref py py-meth docutils literal notranslate"><span class="pre">set_exception()</span></code></a> calls.</p> | |
| </dd></dl> | |
| <dl class="py method"> | |
| <dt class="sig sig-object py" id="asyncio.Future.cancelled"> | |
| <span class="sig-name descname"><span class="pre">cancelled</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Future.cancelled" title="Link to this definition">¶</a></dt> | |
| <dd><p>Return <code class="docutils literal notranslate"><span class="pre">True</span></code> if the Future was <em>cancelled</em>.</p> | |
| <p>The method is usually used to check if a Future is not | |
| <em>cancelled</em> before setting a result or an exception for it:</p> | |
| <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">if</span> <span class="ow">not</span> <span class="n">fut</span><span class="o">.</span><span class="n">cancelled</span><span class="p">():</span> | |
| <span class="n">fut</span><span class="o">.</span><span class="n">set_result</span><span class="p">(</span><span class="mi">42</span><span class="p">)</span> | |
| </pre></div> | |
| </div> | |
| </dd></dl> | |
| <dl class="py method"> | |
| <dt class="sig sig-object py" id="asyncio.Future.add_done_callback"> | |
| <span class="sig-name descname"><span class="pre">add_done_callback</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">callback</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">context</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.Future.add_done_callback" title="Link to this definition">¶</a></dt> | |
| <dd><p>Add a callback to be run when the Future is <em>done</em>.</p> | |
| <p>The <em>callback</em> is called with the Future object as its only | |
| argument.</p> | |
| <p>If the Future is already <em>done</em> when this method is called, | |
| the callback is scheduled with <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.call_soon" title="asyncio.loop.call_soon"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.call_soon()</span></code></a>.</p> | |
| <p>An optional keyword-only <em>context</em> argument allows specifying a | |
| custom <a class="reference internal" href="contextvars.html#contextvars.Context" title="contextvars.Context"><code class="xref py py-class docutils literal notranslate"><span class="pre">contextvars.Context</span></code></a> for the <em>callback</em> to run in. | |
| The current context is used when no <em>context</em> is provided.</p> | |
| <p><a class="reference internal" href="functools.html#functools.partial" title="functools.partial"><code class="xref py py-func docutils literal notranslate"><span class="pre">functools.partial()</span></code></a> can be used to pass parameters | |
| to the callback, e.g.:</p> | |
| <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="c1"># Call 'print("Future:", fut)' when "fut" is done.</span> | |
| <span class="n">fut</span><span class="o">.</span><span class="n">add_done_callback</span><span class="p">(</span> | |
| <span class="n">functools</span><span class="o">.</span><span class="n">partial</span><span class="p">(</span><span class="nb">print</span><span class="p">,</span> <span class="s2">"Future:"</span><span class="p">))</span> | |
| </pre></div> | |
| </div> | |
| <div class="versionchanged"> | |
| <p><span class="versionmodified changed">Changed in version 3.7: </span>The <em>context</em> keyword-only parameter was added. | |
| See <span class="target" id="index-0"></span><a class="pep reference external" href="https://peps.python.org/pep-0567/"><strong>PEP 567</strong></a> for more details.</p> | |
| </div> | |
| </dd></dl> | |
| <dl class="py method"> | |
| <dt class="sig sig-object py" id="asyncio.Future.remove_done_callback"> | |
| <span class="sig-name descname"><span class="pre">remove_done_callback</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">callback</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Future.remove_done_callback" title="Link to this definition">¶</a></dt> | |
| <dd><p>Remove <em>callback</em> from the callbacks list.</p> | |
| <p>Returns the number of callbacks removed, which is typically 1, | |
| unless a callback was added more than once.</p> | |
| </dd></dl> | |
| <dl class="py method"> | |
| <dt class="sig sig-object py" id="asyncio.Future.cancel"> | |
| <span class="sig-name descname"><span class="pre">cancel</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">msg</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.Future.cancel" title="Link to this definition">¶</a></dt> | |
| <dd><p>Cancel the Future and schedule callbacks.</p> | |
| <p>If the Future is already <em>done</em> or <em>cancelled</em>, return <code class="docutils literal notranslate"><span class="pre">False</span></code>. | |
| Otherwise, change the Future’s state to <em>cancelled</em>, | |
| schedule the callbacks, and return <code class="docutils literal notranslate"><span class="pre">True</span></code>.</p> | |
| <div class="versionchanged"> | |
| <p><span class="versionmodified changed">Changed in version 3.9: </span>Added the <em>msg</em> parameter.</p> | |
| </div> | |
| </dd></dl> | |
| <dl class="py method"> | |
| <dt class="sig sig-object py" id="asyncio.Future.exception"> | |
| <span class="sig-name descname"><span class="pre">exception</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Future.exception" title="Link to this definition">¶</a></dt> | |
| <dd><p>Return the exception that was set on this Future.</p> | |
| <p>The exception (or <code class="docutils literal notranslate"><span class="pre">None</span></code> if no exception was set) is | |
| returned only if the Future is <em>done</em>.</p> | |
| <p>If the Future has been <em>cancelled</em>, this method raises a | |
| <a class="reference internal" href="asyncio-exceptions.html#asyncio.CancelledError" title="asyncio.CancelledError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">CancelledError</span></code></a> exception.</p> | |
| <p>If the Future isn’t <em>done</em> yet, this method raises an | |
| <a class="reference internal" href="asyncio-exceptions.html#asyncio.InvalidStateError" title="asyncio.InvalidStateError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">InvalidStateError</span></code></a> exception.</p> | |
| </dd></dl> | |
| <dl class="py method"> | |
| <dt class="sig sig-object py" id="asyncio.Future.get_loop"> | |
| <span class="sig-name descname"><span class="pre">get_loop</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Future.get_loop" title="Link to this definition">¶</a></dt> | |
| <dd><p>Return the event loop the Future object is bound to.</p> | |
| <div class="versionadded"> | |
| <p><span class="versionmodified added">Added in version 3.7.</span></p> | |
| </div> | |
| </dd></dl> | |
| </dd></dl> | |
| <p id="asyncio-example-future">This example creates a Future object, creates and schedules an | |
| asynchronous Task to set result for the Future, and waits until | |
| the Future has a result:</p> | |
| <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">async</span> <span class="k">def</span><span class="w"> </span><span class="nf">set_after</span><span class="p">(</span><span class="n">fut</span><span class="p">,</span> <span class="n">delay</span><span class="p">,</span> <span class="n">value</span><span class="p">):</span> | |
| <span class="c1"># Sleep for *delay* seconds.</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="n">delay</span><span class="p">)</span> | |
| <span class="c1"># Set *value* as a result of *fut* Future.</span> | |
| <span class="n">fut</span><span class="o">.</span><span class="n">set_result</span><span class="p">(</span><span class="n">value</span><span class="p">)</span> | |
| <span class="k">async</span> <span class="k">def</span><span class="w"> </span><span class="nf">main</span><span class="p">():</span> | |
| <span class="c1"># Get the current event loop.</span> | |
| <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> | |
| <span class="c1"># Create a new Future object.</span> | |
| <span class="n">fut</span> <span class="o">=</span> <span class="n">loop</span><span class="o">.</span><span class="n">create_future</span><span class="p">()</span> | |
| <span class="c1"># Run "set_after()" coroutine in a parallel Task.</span> | |
| <span class="c1"># We are using the low-level "loop.create_task()" API here because</span> | |
| <span class="c1"># we already have a reference to the event loop at hand.</span> | |
| <span class="c1"># Otherwise we could have just used "asyncio.create_task()".</span> | |
| <span class="n">loop</span><span class="o">.</span><span class="n">create_task</span><span class="p">(</span> | |
| <span class="n">set_after</span><span class="p">(</span><span class="n">fut</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="s1">'... world'</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="c1"># Wait until *fut* has a result (1 second) and print it.</span> | |
| <span class="nb">print</span><span class="p">(</span><span class="k">await</span> <span class="n">fut</span><span class="p">)</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 class="admonition important"> | |
| <p class="admonition-title">Important</p> | |
| <p>The Future object was designed to mimic | |
| <a class="reference internal" href="concurrent.futures.html#concurrent.futures.Future" title="concurrent.futures.Future"><code class="xref py py-class docutils literal notranslate"><span class="pre">concurrent.futures.Future</span></code></a>. Key differences include:</p> | |
| <ul class="simple"> | |
| <li><p>unlike asyncio Futures, <a class="reference internal" href="concurrent.futures.html#concurrent.futures.Future" title="concurrent.futures.Future"><code class="xref py py-class docutils literal notranslate"><span class="pre">concurrent.futures.Future</span></code></a> | |
| instances cannot be awaited.</p></li> | |
| <li><p><a class="reference internal" href="#asyncio.Future.result" title="asyncio.Future.result"><code class="xref py py-meth docutils literal notranslate"><span class="pre">asyncio.Future.result()</span></code></a> and <a class="reference internal" href="#asyncio.Future.exception" title="asyncio.Future.exception"><code class="xref py py-meth docutils literal notranslate"><span class="pre">asyncio.Future.exception()</span></code></a> | |
| do not accept the <em>timeout</em> argument.</p></li> | |
| <li><p><a class="reference internal" href="#asyncio.Future.result" title="asyncio.Future.result"><code class="xref py py-meth docutils literal notranslate"><span class="pre">asyncio.Future.result()</span></code></a> and <a class="reference internal" href="#asyncio.Future.exception" title="asyncio.Future.exception"><code class="xref py py-meth docutils literal notranslate"><span class="pre">asyncio.Future.exception()</span></code></a> | |
| raise an <a class="reference internal" href="asyncio-exceptions.html#asyncio.InvalidStateError" title="asyncio.InvalidStateError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">InvalidStateError</span></code></a> exception when the Future is not | |
| <em>done</em>.</p></li> | |
| <li><p>Callbacks registered with <a class="reference internal" href="#asyncio.Future.add_done_callback" title="asyncio.Future.add_done_callback"><code class="xref py py-meth docutils literal notranslate"><span class="pre">asyncio.Future.add_done_callback()</span></code></a> | |
| are not called immediately. They are scheduled with | |
| <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.call_soon" title="asyncio.loop.call_soon"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.call_soon()</span></code></a> instead.</p></li> | |
| <li><p>asyncio Future is not compatible with the | |
| <a class="reference internal" href="concurrent.futures.html#concurrent.futures.wait" title="concurrent.futures.wait"><code class="xref py py-func docutils literal notranslate"><span class="pre">concurrent.futures.wait()</span></code></a> and | |
| <a class="reference internal" href="concurrent.futures.html#concurrent.futures.as_completed" title="concurrent.futures.as_completed"><code class="xref py py-func docutils literal notranslate"><span class="pre">concurrent.futures.as_completed()</span></code></a> functions.</p></li> | |
| <li><p><a class="reference internal" href="#asyncio.Future.cancel" title="asyncio.Future.cancel"><code class="xref py py-meth docutils literal notranslate"><span class="pre">asyncio.Future.cancel()</span></code></a> accepts an optional <code class="docutils literal notranslate"><span class="pre">msg</span></code> argument, | |
| but <a class="reference internal" href="concurrent.futures.html#concurrent.futures.Future.cancel" title="concurrent.futures.Future.cancel"><code class="xref py py-meth docutils literal notranslate"><span class="pre">concurrent.futures.Future.cancel()</span></code></a> does not.</p></li> | |
| </ul> | |
| </div> | |
| </section> | |
| </section> | |
| <div class="clearer"></div> | |
| </div> | |
| </div> | |
| </div> | |
| <div class="sphinxsidebar" role="navigation" aria-label="Main"> | |
| <div class="sphinxsidebarwrapper"> | |
| <div> | |
| <h3><a href="../contents.html">Table of Contents</a></h3> | |
| <ul> | |
| <li><a class="reference internal" href="#">Futures</a><ul> | |
| <li><a class="reference internal" href="#future-functions">Future Functions</a></li> | |
| <li><a class="reference internal" href="#future-object">Future Object</a></li> | |
| </ul> | |
| </li> | |
| </ul> | |
| </div> | |
| <div> | |
| <h4>Previous topic</h4> | |
| <p class="topless"><a href="asyncio-eventloop.html" | |
| title="previous chapter">Event Loop</a></p> | |
| </div> | |
| <div> | |
| <h4>Next topic</h4> | |
| <p class="topless"><a href="asyncio-protocol.html" | |
| title="next chapter">Transports and Protocols</a></p> | |
| </div> | |
| <script> | |
| document.addEventListener('DOMContentLoaded', () => { | |
| const title = document.querySelector('meta[property="og:title"]').content; | |
| const elements = document.querySelectorAll('.improvepage'); | |
| const pageurl = window.location.href.split('?')[0]; | |
| elements.forEach(element => { | |
| const url = new URL(element.href.split('?')[0].replace("-nojs", "")); | |
| url.searchParams.set('pagetitle', title); | |
| url.searchParams.set('pageurl', pageurl); | |
| url.searchParams.set('pagesource', "library/asyncio-future.rst"); | |
| element.href = url.toString(); | |
| }); | |
| }); | |
| </script> | |
| <div role="note" aria-label="source link"> | |
| <h3>This page</h3> | |
| <ul class="this-page-menu"> | |
| <li><a href="../bugs.html">Report a bug</a></li> | |
| <li><a class="improvepage" href="../improve-page-nojs.html">Improve this page</a></li> | |
| <li> | |
| <a href="https://github.com/python/cpython/blob/main/Doc/library/asyncio-future.rst?plain=1" | |
| rel="nofollow">Show source | |
| </a> | |
| </li> | |
| </ul> | |
| </div> | |
| </div> | |
| <div id="sidebarbutton" title="Collapse sidebar"> | |
| <span>«</span> | |
| </div> | |
| </div> | |
| <div class="clearer"></div> | |
| </div> | |
| <div class="related" role="navigation" aria-label="Related"> | |
| <h3>Navigation</h3> | |
| <ul> | |
| <li class="right" style="margin-right: 10px"> | |
| <a href="../genindex.html" title="General Index" | |
| >index</a></li> | |
| <li class="right" > | |
| <a href="../py-modindex.html" title="Python Module Index" | |
| >modules</a> |</li> | |
| <li class="right" > | |
| <a href="asyncio-protocol.html" title="Transports and Protocols" | |
| >next</a> |</li> | |
| <li class="right" > | |
| <a href="asyncio-eventloop.html" title="Event Loop" | |
| >previous</a> |</li> | |
| <li><img src="../_static/py.svg" alt="Python logo" style="vertical-align: middle; margin-top: -1px"></li> | |
| <li><a href="https://www.python.org/">Python</a> »</li> | |
| <li class="switchers"> | |
| <div class="language_switcher_placeholder"></div> | |
| <div class="version_switcher_placeholder"></div> | |
| </li> | |
| <li> | |
| </li> | |
| <li id="cpython-language-and-version"> | |
| <a href="../index.html">3.15.0a6 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" >Networking and Interprocess Communication</a> »</li> | |
| <li class="nav-item nav-item-3"><a href="asyncio.html" ><code class="xref py py-mod docutils literal notranslate"><span class="pre">asyncio</span></code> — Asynchronous I/O</a> »</li> | |
| <li class="nav-item nav-item-this"><a href="">Futures</a></li> | |
| <li class="right"> | |
| <div class="inline-search" role="search"> | |
| <form class="inline-search" action="../search.html" method="get"> | |
| <input placeholder="Quick search" aria-label="Quick search" type="search" name="q" id="search-box"> | |
| <input type="submit" value="Go"> | |
| </form> | |
| </div> | |
| | | |
| </li> | |
| <li class="right"> | |
| <label class="theme-selector-label"> | |
| Theme | |
| <select class="theme-selector" oninput="activateTheme(this.value)"> | |
| <option value="auto" selected>Auto</option> | |
| <option value="light">Light</option> | |
| <option value="dark">Dark</option> | |
| </select> | |
| </label> |</li> | |
| </ul> | |
| </div> | |
| <div class="footer"> | |
| © <a href="../copyright.html">Copyright</a> 2001 Python Software Foundation. | |
| <br> | |
| This page is licensed under the Python Software Foundation License Version 2. | |
| <br> | |
| Examples, recipes, and other code in the documentation are additionally licensed under the Zero Clause BSD License. | |
| <br> | |
| See <a href="/license.html">History and License</a> for more information.<br> | |
| <br> | |
| The Python Software Foundation is a non-profit corporation. | |
| <a href="https://www.python.org/psf/donations/">Please donate.</a> | |
| <br> | |
| <br> | |
| Last updated on Mar 10, 2026 (08:58 UTC). | |
| <a href="/bugs.html">Found a bug</a>? | |
| <br> | |
| Created using <a href="https://www.sphinx-doc.org/">Sphinx</a> 8.2.3. | |
| </div> | |
| </body> | |
| </html> |