Baoding-FenShuaJiang
/
Green_GoodERP18_FSJ_Standard
보기 1
좋아요 0
위키 捐赠
gooderp18绿色标准版
You can not select more than 25 topics Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
브렌치: master
브랜치 태그
${ item.name }
Create branch ${ searchTerm }
from 'master'
${ noResults }
Green_GoodERP18_FSJ_Standard/python/Doc/html/library/asyncio-dev.html

552 lines
39KB
Raw 고유링크 Blame 히스토리 

  1. <!DOCTYPE html>

  2. 

  3. <html lang="en" data-content_root="../">

  4.   <head>

  5.     <meta charset="utf-8" />

  6.     <meta name="viewport" content="width=device-width, initial-scale=1.0" /><meta name="viewport" content="width=device-width, initial-scale=1" />

  7. <meta property="og:title" content="Developing with asyncio" />

  8. <meta property="og:type" content="website" />

  9. <meta property="og:url" content="https://docs.python.org/3/library/asyncio-dev.html" />

  10. <meta property="og:site_name" content="Python documentation" />

  11. <meta property="og:description" content="Asynchronous programming is different from classic “sequential” programming. This page lists common mistakes and traps and explains how to avoid them. Debug Mode: By default asyncio runs in product..." />

  12. <meta property="og:image" content="https://docs.python.org/3/_static/og-image.png" />

  13. <meta property="og:image:alt" content="Python documentation" />

  14. <meta name="description" content="Asynchronous programming is different from classic “sequential” programming. This page lists common mistakes and traps and explains how to avoid them. Debug Mode: By default asyncio runs in product..." />

  15. <meta property="og:image:width" content="200" />

  16. <meta property="og:image:height" content="200" />

  17. <meta name="theme-color" content="#3776ab" />

  18. 

  19.     <title>Developing with asyncio &#8212; Python 3.12.3 documentation</title><meta name="viewport" content="width=device-width, initial-scale=1.0">

  20.     

  21.     <link rel="stylesheet" type="text/css" href="../_static/pygments.css?v=80d5e7a1" />

  22.     <link rel="stylesheet" type="text/css" href="../_static/pydoctheme.css?v=bb723527" />

  23.     <link id="pygments_dark_css" media="(prefers-color-scheme: dark)" rel="stylesheet" type="text/css" href="../_static/pygments_dark.css?v=b20cc3f5" />

  24.     

  25.     <script src="../_static/documentation_options.js?v=2c828074"></script>

  26.     <script src="../_static/doctools.js?v=888ff710"></script>

  27.     <script src="../_static/sphinx_highlight.js?v=dc90522c"></script>

  28.     

  29.     <script src="../_static/sidebar.js"></script>

  30.     

  31.     <link rel="search" type="application/opensearchdescription+xml"

  32.           title="Search within Python 3.12.3 documentation"

  33.           href="../_static/opensearch.xml"/>

  34.     <link rel="author" title="About these documents" href="../about.html" />

  35.     <link rel="index" title="Index" href="../genindex.html" />

  36.     <link rel="search" title="Search" href="../search.html" />

  37.     <link rel="copyright" title="Copyright" href="../copyright.html" />

  38.     <link rel="next" title="socket — Low-level networking interface" href="socket.html" />

  39.     <link rel="prev" title="Low-level API Index" href="asyncio-llapi-index.html" />

  40.     <link rel="canonical" href="https://docs.python.org/3/library/asyncio-dev.html" />

  41.     

  42.       

  43.     

  44. 

  45.     

  46.     <style>

  47.       @media only screen {

  48.         table.full-width-table {

  49.             width: 100%;

  50.         }

  51.       }

  52.     </style>

  53. <link rel="stylesheet" href="../_static/pydoctheme_dark.css" media="(prefers-color-scheme: dark)" id="pydoctheme_dark_css">

  54.     <link rel="shortcut icon" type="image/png" href="../_static/py.svg" />

  55.             <script type="text/javascript" src="../_static/copybutton.js"></script>

  56.             <script type="text/javascript" src="../_static/menu.js"></script>

  57.             <script type="text/javascript" src="../_static/search-focus.js"></script>

  58.             <script type="text/javascript" src="../_static/themetoggle.js"></script> 

  59. 

  60.   </head>

  61. <body>

  62. <div class="mobile-nav">

  63.     <input type="checkbox" id="menuToggler" class="toggler__input" aria-controls="navigation"

  64.            aria-pressed="false" aria-expanded="false" role="button" aria-label="Menu" />

  65.     <nav class="nav-content" role="navigation">

  66.         <label for="menuToggler" class="toggler__label">

  67.             <span></span>

  68.         </label>

  69.         <span class="nav-items-wrapper">

  70.             <a href="https://www.python.org/" class="nav-logo">

  71.                 <img src="../_static/py.svg" alt="Python logo"/>

  72.             </a>

  73.             <span class="version_switcher_placeholder"></span>

  74.             <form role="search" class="search" action="../search.html" method="get">

  75.                 <svg xmlns="http://www.w3.org/2000/svg" width="20" height="20" viewBox="0 0 24 24" class="search-icon">

  76.                     <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>

  77.                 </svg>

  78.                 <input placeholder="Quick search" aria-label="Quick search" type="search" name="q" />

  79.                 <input type="submit" value="Go"/>

  80.             </form>

  81.         </span>

  82.     </nav>

  83.     <div class="menu-wrapper">

  84.         <nav class="menu" role="navigation" aria-label="main navigation">

  85.             <div class="language_switcher_placeholder"></div>

  86.             

  87. <label class="theme-selector-label">

  88.     Theme

  89.     <select class="theme-selector" oninput="activateTheme(this.value)">

  90.         <option value="auto" selected>Auto</option>

  91.         <option value="light">Light</option>

  92.         <option value="dark">Dark</option>

  93.     </select>

  94. </label>

  95.   <div>

  96.     <h3><a href="../contents.html">Table of Contents</a></h3>

  97.     <ul>

  98. <li><a class="reference internal" href="#">Developing with asyncio</a><ul>

  99. <li><a class="reference internal" href="#debug-mode">Debug Mode</a></li>

  100. <li><a class="reference internal" href="#concurrency-and-multithreading">Concurrency and Multithreading</a></li>

  101. <li><a class="reference internal" href="#running-blocking-code">Running Blocking Code</a></li>

  102. <li><a class="reference internal" href="#logging">Logging</a></li>

  103. <li><a class="reference internal" href="#detect-never-awaited-coroutines">Detect never-awaited coroutines</a></li>

  104. <li><a class="reference internal" href="#detect-never-retrieved-exceptions">Detect never-retrieved exceptions</a></li>

  105. </ul>

  106. </li>

  107. </ul>

  108. 

  109.   </div>

  110.   <div>

  111.     <h4>Previous topic</h4>

  112.     <p class="topless"><a href="asyncio-llapi-index.html"

  113.                           title="previous chapter">Low-level API Index</a></p>

  114.   </div>

  115.   <div>

  116.     <h4>Next topic</h4>

  117.     <p class="topless"><a href="socket.html"

  118.                           title="next chapter"><code class="xref py py-mod docutils literal notranslate"><span class="pre">socket</span></code> — Low-level networking interface</a></p>

  119.   </div>

  120.   <div role="note" aria-label="source link">

  121.     <h3>This Page</h3>

  122.     <ul class="this-page-menu">

  123.       <li><a href="../bugs.html">Report a Bug</a></li>

  124.       <li>

  125.         <a href="https://github.com/python/cpython/blob/main/Doc/library/asyncio-dev.rst"

  126.             rel="nofollow">Show Source

  127.         </a>

  128.       </li>

  129.     </ul>

  130.   </div>

  131.         </nav>

  132.     </div>

  133. </div>

  134. 

  135.   

  136.     <div class="related" role="navigation" aria-label="related navigation">

  137.       <h3>Navigation</h3>

  138.       <ul>

  139.         <li class="right" style="margin-right: 10px">

  140.           <a href="../genindex.html" title="General Index"

  141.              accesskey="I">index</a></li>

  142.         <li class="right" >

  143.           <a href="../py-modindex.html" title="Python Module Index"

  144.              >modules</a> |</li>

  145.         <li class="right" >

  146.           <a href="socket.html" title="socket — Low-level networking interface"

  147.              accesskey="N">next</a> |</li>

  148.         <li class="right" >

  149.           <a href="asyncio-llapi-index.html" title="Low-level API Index"

  150.              accesskey="P">previous</a> |</li>

  151. 

  152.           <li><img src="../_static/py.svg" alt="Python logo" style="vertical-align: middle; margin-top: -1px"/></li>

  153.           <li><a href="https://www.python.org/">Python</a> &#187;</li>

  154.           <li class="switchers">

  155.             <div class="language_switcher_placeholder"></div>

  156.             <div class="version_switcher_placeholder"></div>

  157.           </li>

  158.           <li>

  159.               

  160.           </li>

  161.     <li id="cpython-language-and-version">

  162.       <a href="../index.html">3.12.3 Documentation</a> &#187;

  163.     </li>

  164. 

  165.           <li class="nav-item nav-item-1"><a href="index.html" >The Python Standard Library</a> &#187;</li>

  166.           <li class="nav-item nav-item-2"><a href="ipc.html" >Networking and Interprocess Communication</a> &#187;</li>

  167.           <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> &#187;</li>

  168.         <li class="nav-item nav-item-this"><a href="">Developing with asyncio</a></li>

  169.                 <li class="right">

  170.                     

  171. 

  172.     <div class="inline-search" role="search">

  173.         <form class="inline-search" action="../search.html" method="get">

  174.           <input placeholder="Quick search" aria-label="Quick search" type="search" name="q" id="search-box" />

  175.           <input type="submit" value="Go" />

  176.         </form>

  177.     </div>

  178.                      |

  179.                 </li>

  180.             <li class="right">

  181. <label class="theme-selector-label">

  182.     Theme

  183.     <select class="theme-selector" oninput="activateTheme(this.value)">

  184.         <option value="auto" selected>Auto</option>

  185.         <option value="light">Light</option>

  186.         <option value="dark">Dark</option>

  187.     </select>

  188. </label> |</li>

  189.             

  190.       </ul>

  191.     </div>    

  192. 

  193.     <div class="document">

  194.       <div class="documentwrapper">

  195.         <div class="bodywrapper">

  196.           <div class="body" role="main">

  197.             

  198.   <section id="developing-with-asyncio">

  199. <span id="asyncio-dev"></span><h1>Developing with asyncio<a class="headerlink" href="#developing-with-asyncio" title="Link to this heading">¶</a></h1>

  200. <p>Asynchronous programming is different from classic “sequential”

  201. programming.</p>

  202. <p>This page lists common mistakes and traps and explains how

  203. to avoid them.</p>

  204. <section id="debug-mode">

  205. <span id="asyncio-debug-mode"></span><h2>Debug Mode<a class="headerlink" href="#debug-mode" title="Link to this heading">¶</a></h2>

  206. <p>By default asyncio runs in production mode.  In order to ease

  207. the development asyncio has a <em>debug mode</em>.</p>

  208. <p>There are several ways to enable asyncio debug mode:</p>

  209. <ul class="simple">

  210. <li><p>Setting the <span class="target" id="index-0"></span><a class="reference internal" href="../using/cmdline.html#envvar-PYTHONASYNCIODEBUG"><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PYTHONASYNCIODEBUG</span></code></a> environment variable to <code class="docutils literal notranslate"><span class="pre">1</span></code>.</p></li>

  211. <li><p>Using the <a class="reference internal" href="devmode.html#devmode"><span class="std std-ref">Python Development Mode</span></a>.</p></li>

  212. <li><p>Passing <code class="docutils literal notranslate"><span class="pre">debug=True</span></code> to <a class="reference internal" href="asyncio-runner.html#asyncio.run" title="asyncio.run"><code class="xref py py-func docutils literal notranslate"><span class="pre">asyncio.run()</span></code></a>.</p></li>

  213. <li><p>Calling <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.set_debug" title="asyncio.loop.set_debug"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.set_debug()</span></code></a>.</p></li>

  214. </ul>

  215. <p>In addition to enabling the debug mode, consider also:</p>

  216. <ul>

  217. <li><p>setting the log level of the <a class="reference internal" href="#asyncio-logger"><span class="std std-ref">asyncio logger</span></a> to

  218. <a class="reference internal" href="logging.html#logging.DEBUG" title="logging.DEBUG"><code class="xref py py-const docutils literal notranslate"><span class="pre">logging.DEBUG</span></code></a>, for example the following snippet of code

  219. can be run at startup of the application:</p>

  220. <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">logging</span><span class="o">.</span><span class="n">basicConfig</span><span class="p">(</span><span class="n">level</span><span class="o">=</span><span class="n">logging</span><span class="o">.</span><span class="n">DEBUG</span><span class="p">)</span>

  221. </pre></div>

  222. </div>

  223. </li>

  224. <li><p>configuring the <a class="reference internal" href="warnings.html#module-warnings" title="warnings: Issue warning messages and control their disposition."><code class="xref py py-mod docutils literal notranslate"><span class="pre">warnings</span></code></a> module to display

  225. <a class="reference internal" href="exceptions.html#ResourceWarning" title="ResourceWarning"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ResourceWarning</span></code></a> warnings.  One way of doing that is by

  226. using the <a class="reference internal" href="../using/cmdline.html#cmdoption-W"><code class="xref std std-option docutils literal notranslate"><span class="pre">-W</span></code></a> <code class="docutils literal notranslate"><span class="pre">default</span></code> command line option.</p></li>

  227. </ul>

  228. <p>When the debug mode is enabled:</p>

  229. <ul class="simple">

  230. <li><p>asyncio checks for <a class="reference internal" href="#asyncio-coroutine-not-scheduled"><span class="std std-ref">coroutines that were not awaited</span></a> and logs them; this mitigates

  231. the “forgotten await” pitfall.</p></li>

  232. <li><p>Many non-threadsafe asyncio APIs (such as <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> and

  233. <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.call_at" title="asyncio.loop.call_at"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.call_at()</span></code></a> methods) raise an exception if they are called

  234. from a wrong thread.</p></li>

  235. <li><p>The execution time of the I/O selector is logged if it takes too long to

  236. perform an I/O operation.</p></li>

  237. <li><p>Callbacks taking longer than 100 milliseconds are logged.  The

  238. <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.slow_callback_duration" title="asyncio.loop.slow_callback_duration"><code class="xref py py-attr docutils literal notranslate"><span class="pre">loop.slow_callback_duration</span></code></a> attribute can be used to set the

  239. minimum execution duration in seconds that is considered “slow”.</p></li>

  240. </ul>

  241. </section>

  242. <section id="concurrency-and-multithreading">

  243. <span id="asyncio-multithreading"></span><h2>Concurrency and Multithreading<a class="headerlink" href="#concurrency-and-multithreading" title="Link to this heading">¶</a></h2>

  244. <p>An event loop runs in a thread (typically the main thread) and executes

  245. all callbacks and Tasks in its thread.  While a Task is running in the

  246. event loop, no other Tasks can run in the same thread.  When a Task

  247. executes an <code class="docutils literal notranslate"><span class="pre">await</span></code> expression, the running Task gets suspended, and

  248. the event loop executes the next Task.</p>

  249. <p>To schedule a <a class="reference internal" href="../glossary.html#term-callback"><span class="xref std std-term">callback</span></a> from another OS thread, the

  250. <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.call_soon_threadsafe" title="asyncio.loop.call_soon_threadsafe"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.call_soon_threadsafe()</span></code></a> method should be used. Example:</p>

  251. <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">loop</span><span class="o">.</span><span class="n">call_soon_threadsafe</span><span class="p">(</span><span class="n">callback</span><span class="p">,</span> <span class="o">*</span><span class="n">args</span><span class="p">)</span>

  252. </pre></div>

  253. </div>

  254. <p>Almost all asyncio objects are not thread safe, which is typically

  255. not a problem unless there is code that works with them from outside

  256. of a Task or a callback.  If there’s a need for such code to call a

  257. low-level asyncio API, the <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.call_soon_threadsafe" title="asyncio.loop.call_soon_threadsafe"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.call_soon_threadsafe()</span></code></a> method

  258. should be used, e.g.:</p>

  259. <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">loop</span><span class="o">.</span><span class="n">call_soon_threadsafe</span><span class="p">(</span><span class="n">fut</span><span class="o">.</span><span class="n">cancel</span><span class="p">)</span>

  260. </pre></div>

  261. </div>

  262. <p>To schedule a coroutine object from a different OS thread, the

  263. <a class="reference internal" href="asyncio-task.html#asyncio.run_coroutine_threadsafe" title="asyncio.run_coroutine_threadsafe"><code class="xref py py-func docutils literal notranslate"><span class="pre">run_coroutine_threadsafe()</span></code></a> function should be used. It returns a

  264. <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> to access the result:</p>

  265. <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">async</span> <span class="k">def</span> <span class="nf">coro_func</span><span class="p">():</span>

  266.      <span class="k">return</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="mi">42</span><span class="p">)</span>

  267. 

  268. <span class="c1"># Later in another OS thread:</span>

  269. 

  270. <span class="n">future</span> <span class="o">=</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">run_coroutine_threadsafe</span><span class="p">(</span><span class="n">coro_func</span><span class="p">(),</span> <span class="n">loop</span><span class="p">)</span>

  271. <span class="c1"># Wait for the result:</span>

  272. <span class="n">result</span> <span class="o">=</span> <span class="n">future</span><span class="o">.</span><span class="n">result</span><span class="p">()</span>

  273. </pre></div>

  274. </div>

  275. <p>To handle signals the event loop must be

  276. run in the main thread.</p>

  277. <p>The <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.run_in_executor" title="asyncio.loop.run_in_executor"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.run_in_executor()</span></code></a> method can be used with a

  278. <a class="reference internal" href="concurrent.futures.html#concurrent.futures.ThreadPoolExecutor" title="concurrent.futures.ThreadPoolExecutor"><code class="xref py py-class docutils literal notranslate"><span class="pre">concurrent.futures.ThreadPoolExecutor</span></code></a> to execute

  279. blocking code in a different OS thread without blocking the OS thread

  280. that the event loop runs in.</p>

  281. <p>There is currently no way to schedule coroutines or callbacks directly

  282. from a different process (such as one started with

  283. <a class="reference internal" href="multiprocessing.html#module-multiprocessing" title="multiprocessing: Process-based parallelism."><code class="xref py py-mod docutils literal notranslate"><span class="pre">multiprocessing</span></code></a>). The <a class="reference internal" href="asyncio-eventloop.html#asyncio-event-loop-methods"><span class="std std-ref">Event Loop Methods</span></a>

  284. section lists APIs that can read from pipes and watch file descriptors

  285. without blocking the event loop. In addition, asyncio’s

  286. <a class="reference internal" href="asyncio-subprocess.html#asyncio-subprocess"><span class="std std-ref">Subprocess</span></a> APIs provide a way to start a

  287. process and communicate with it from the event loop. Lastly, the

  288. aforementioned <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.run_in_executor" title="asyncio.loop.run_in_executor"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.run_in_executor()</span></code></a> method can also be used

  289. with a <a class="reference internal" href="concurrent.futures.html#concurrent.futures.ProcessPoolExecutor" title="concurrent.futures.ProcessPoolExecutor"><code class="xref py py-class docutils literal notranslate"><span class="pre">concurrent.futures.ProcessPoolExecutor</span></code></a> to execute

  290. code in a different process.</p>

  291. </section>

  292. <section id="running-blocking-code">

  293. <span id="asyncio-handle-blocking"></span><h2>Running Blocking Code<a class="headerlink" href="#running-blocking-code" title="Link to this heading">¶</a></h2>

  294. <p>Blocking (CPU-bound) code should not be called directly.  For example,

  295. if a function performs a CPU-intensive calculation for 1 second,

  296. all concurrent asyncio Tasks and IO operations would be delayed

  297. by 1 second.</p>

  298. <p>An executor can be used to run a task in a different thread or even in

  299. a different process to avoid blocking the OS thread with the

  300. event loop.  See the <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.run_in_executor" title="asyncio.loop.run_in_executor"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.run_in_executor()</span></code></a> method for more

  301. details.</p>

  302. </section>

  303. <section id="logging">

  304. <span id="asyncio-logger"></span><h2>Logging<a class="headerlink" href="#logging" title="Link to this heading">¶</a></h2>

  305. <p>asyncio uses the <a class="reference internal" href="logging.html#module-logging" title="logging: Flexible event logging system for applications."><code class="xref py py-mod docutils literal notranslate"><span class="pre">logging</span></code></a> module and all logging is performed

  306. via the <code class="docutils literal notranslate"><span class="pre">&quot;asyncio&quot;</span></code> logger.</p>

  307. <p>The default log level is <a class="reference internal" href="logging.html#logging.INFO" title="logging.INFO"><code class="xref py py-const docutils literal notranslate"><span class="pre">logging.INFO</span></code></a>, which can be easily

  308. adjusted:</p>

  309. <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">logging</span><span class="o">.</span><span class="n">getLogger</span><span class="p">(</span><span class="s2">&quot;asyncio&quot;</span><span class="p">)</span><span class="o">.</span><span class="n">setLevel</span><span class="p">(</span><span class="n">logging</span><span class="o">.</span><span class="n">WARNING</span><span class="p">)</span>

  310. </pre></div>

  311. </div>

  312. <p>Network logging can block the event loop. It is recommended to use

  313. a separate thread for handling logs or use non-blocking IO. For example,

  314. see <a class="reference internal" href="../howto/logging-cookbook.html#blocking-handlers"><span class="std std-ref">Dealing with handlers that block</span></a>.</p>

  315. </section>

  316. <section id="detect-never-awaited-coroutines">

  317. <span id="asyncio-coroutine-not-scheduled"></span><h2>Detect never-awaited coroutines<a class="headerlink" href="#detect-never-awaited-coroutines" title="Link to this heading">¶</a></h2>

  318. <p>When a coroutine function is called, but not awaited

  319. (e.g. <code class="docutils literal notranslate"><span class="pre">coro()</span></code> instead of <code class="docutils literal notranslate"><span class="pre">await</span> <span class="pre">coro()</span></code>)

  320. or the coroutine is not scheduled with <a class="reference internal" href="asyncio-task.html#asyncio.create_task" title="asyncio.create_task"><code class="xref py py-meth docutils literal notranslate"><span class="pre">asyncio.create_task()</span></code></a>, asyncio

  321. will emit a <a class="reference internal" href="exceptions.html#RuntimeWarning" title="RuntimeWarning"><code class="xref py py-exc docutils literal notranslate"><span class="pre">RuntimeWarning</span></code></a>:</p>

  322. <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">asyncio</span>

  323. 

  324. <span class="k">async</span> <span class="k">def</span> <span class="nf">test</span><span class="p">():</span>

  325.     <span class="nb">print</span><span class="p">(</span><span class="s2">&quot;never scheduled&quot;</span><span class="p">)</span>

  326. 

  327. <span class="k">async</span> <span class="k">def</span> <span class="nf">main</span><span class="p">():</span>

  328.     <span class="n">test</span><span class="p">()</span>

  329. 

  330. <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>

  331. </pre></div>

  332. </div>

  333. <p>Output:</p>

  334. <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">test</span><span class="o">.</span><span class="n">py</span><span class="p">:</span><span class="mi">7</span><span class="p">:</span> <span class="ne">RuntimeWarning</span><span class="p">:</span> <span class="n">coroutine</span> <span class="s1">&#39;test&#39;</span> <span class="n">was</span> <span class="n">never</span> <span class="n">awaited</span>

  335.   <span class="n">test</span><span class="p">()</span>

  336. </pre></div>

  337. </div>

  338. <p>Output in debug mode:</p>

  339. <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">test</span><span class="o">.</span><span class="n">py</span><span class="p">:</span><span class="mi">7</span><span class="p">:</span> <span class="ne">RuntimeWarning</span><span class="p">:</span> <span class="n">coroutine</span> <span class="s1">&#39;test&#39;</span> <span class="n">was</span> <span class="n">never</span> <span class="n">awaited</span>

  340. <span class="n">Coroutine</span> <span class="n">created</span> <span class="n">at</span> <span class="p">(</span><span class="n">most</span> <span class="n">recent</span> <span class="n">call</span> <span class="n">last</span><span class="p">)</span>

  341.   <span class="n">File</span> <span class="s2">&quot;../t.py&quot;</span><span class="p">,</span> <span class="n">line</span> <span class="mi">9</span><span class="p">,</span> <span class="ow">in</span> <span class="o">&lt;</span><span class="n">module</span><span class="o">&gt;</span>

  342.     <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> <span class="n">debug</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span>

  343. 

  344.   <span class="o">&lt;</span> <span class="o">..</span> <span class="o">&gt;</span>

  345. 

  346.   <span class="n">File</span> <span class="s2">&quot;../t.py&quot;</span><span class="p">,</span> <span class="n">line</span> <span class="mi">7</span><span class="p">,</span> <span class="ow">in</span> <span class="n">main</span>

  347.     <span class="n">test</span><span class="p">()</span>

  348.   <span class="n">test</span><span class="p">()</span>

  349. </pre></div>

  350. </div>

  351. <p>The usual fix is to either await the coroutine or call the

  352. <a class="reference internal" href="asyncio-task.html#asyncio.create_task" title="asyncio.create_task"><code class="xref py py-meth docutils literal notranslate"><span class="pre">asyncio.create_task()</span></code></a> function:</p>

  353. <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">async</span> <span class="k">def</span> <span class="nf">main</span><span class="p">():</span>

  354.     <span class="k">await</span> <span class="n">test</span><span class="p">()</span>

  355. </pre></div>

  356. </div>

  357. </section>

  358. <section id="detect-never-retrieved-exceptions">

  359. <h2>Detect never-retrieved exceptions<a class="headerlink" href="#detect-never-retrieved-exceptions" title="Link to this heading">¶</a></h2>

  360. <p>If a <a class="reference internal" href="asyncio-future.html#asyncio.Future.set_exception" title="asyncio.Future.set_exception"><code class="xref py py-meth docutils literal notranslate"><span class="pre">Future.set_exception()</span></code></a> is called but the Future object is

  361. never awaited on, the exception would never be propagated to the

  362. user code.  In this case, asyncio would emit a log message when the

  363. Future object is garbage collected.</p>

  364. <p>Example of an unhandled exception:</p>

  365. <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">asyncio</span>

  366. 

  367. <span class="k">async</span> <span class="k">def</span> <span class="nf">bug</span><span class="p">():</span>

  368.     <span class="k">raise</span> <span class="ne">Exception</span><span class="p">(</span><span class="s2">&quot;not consumed&quot;</span><span class="p">)</span>

  369. 

  370. <span class="k">async</span> <span class="k">def</span> <span class="nf">main</span><span class="p">():</span>

  371.     <span class="n">asyncio</span><span class="o">.</span><span class="n">create_task</span><span class="p">(</span><span class="n">bug</span><span class="p">())</span>

  372. 

  373. <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>

  374. </pre></div>

  375. </div>

  376. <p>Output:</p>

  377. <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">Task</span> <span class="n">exception</span> <span class="n">was</span> <span class="n">never</span> <span class="n">retrieved</span>

  378. <span class="n">future</span><span class="p">:</span> <span class="o">&lt;</span><span class="n">Task</span> <span class="n">finished</span> <span class="n">coro</span><span class="o">=&lt;</span><span class="n">bug</span><span class="p">()</span> <span class="n">done</span><span class="p">,</span> <span class="n">defined</span> <span class="n">at</span> <span class="n">test</span><span class="o">.</span><span class="n">py</span><span class="p">:</span><span class="mi">3</span><span class="o">&gt;</span>

  379.   <span class="n">exception</span><span class="o">=</span><span class="ne">Exception</span><span class="p">(</span><span class="s1">&#39;not consumed&#39;</span><span class="p">)</span><span class="o">&gt;</span>

  380. 

  381. <span class="n">Traceback</span> <span class="p">(</span><span class="n">most</span> <span class="n">recent</span> <span class="n">call</span> <span class="n">last</span><span class="p">):</span>

  382.   <span class="n">File</span> <span class="s2">&quot;test.py&quot;</span><span class="p">,</span> <span class="n">line</span> <span class="mi">4</span><span class="p">,</span> <span class="ow">in</span> <span class="n">bug</span>

  383.     <span class="k">raise</span> <span class="ne">Exception</span><span class="p">(</span><span class="s2">&quot;not consumed&quot;</span><span class="p">)</span>

  384. <span class="ne">Exception</span><span class="p">:</span> <span class="ow">not</span> <span class="n">consumed</span>

  385. </pre></div>

  386. </div>

  387. <p><a class="reference internal" href="#asyncio-debug-mode"><span class="std std-ref">Enable the debug mode</span></a> to get the

  388. traceback where the task was created:</p>

  389. <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></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> <span class="n">debug</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span>

  390. </pre></div>

  391. </div>

  392. <p>Output in debug mode:</p>

  393. <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">Task</span> <span class="n">exception</span> <span class="n">was</span> <span class="n">never</span> <span class="n">retrieved</span>

  394. <span class="n">future</span><span class="p">:</span> <span class="o">&lt;</span><span class="n">Task</span> <span class="n">finished</span> <span class="n">coro</span><span class="o">=&lt;</span><span class="n">bug</span><span class="p">()</span> <span class="n">done</span><span class="p">,</span> <span class="n">defined</span> <span class="n">at</span> <span class="n">test</span><span class="o">.</span><span class="n">py</span><span class="p">:</span><span class="mi">3</span><span class="o">&gt;</span>

  395.     <span class="n">exception</span><span class="o">=</span><span class="ne">Exception</span><span class="p">(</span><span class="s1">&#39;not consumed&#39;</span><span class="p">)</span> <span class="n">created</span> <span class="n">at</span> <span class="n">asyncio</span><span class="o">/</span><span class="n">tasks</span><span class="o">.</span><span class="n">py</span><span class="p">:</span><span class="mi">321</span><span class="o">&gt;</span>

  396. 

  397. <span class="n">source_traceback</span><span class="p">:</span> <span class="n">Object</span> <span class="n">created</span> <span class="n">at</span> <span class="p">(</span><span class="n">most</span> <span class="n">recent</span> <span class="n">call</span> <span class="n">last</span><span class="p">):</span>

  398.   <span class="n">File</span> <span class="s2">&quot;../t.py&quot;</span><span class="p">,</span> <span class="n">line</span> <span class="mi">9</span><span class="p">,</span> <span class="ow">in</span> <span class="o">&lt;</span><span class="n">module</span><span class="o">&gt;</span>

  399.     <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> <span class="n">debug</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span>

  400. 

  401. <span class="o">&lt;</span> <span class="o">..</span> <span class="o">&gt;</span>

  402. 

  403. <span class="n">Traceback</span> <span class="p">(</span><span class="n">most</span> <span class="n">recent</span> <span class="n">call</span> <span class="n">last</span><span class="p">):</span>

  404.   <span class="n">File</span> <span class="s2">&quot;../t.py&quot;</span><span class="p">,</span> <span class="n">line</span> <span class="mi">4</span><span class="p">,</span> <span class="ow">in</span> <span class="n">bug</span>

  405.     <span class="k">raise</span> <span class="ne">Exception</span><span class="p">(</span><span class="s2">&quot;not consumed&quot;</span><span class="p">)</span>

  406. <span class="ne">Exception</span><span class="p">:</span> <span class="ow">not</span> <span class="n">consumed</span>

  407. </pre></div>

  408. </div>

  409. </section>

  410. </section>

  411. 

  412. 

  413.             <div class="clearer"></div>

  414.           </div>

  415.         </div>

  416.       </div>

  417.       <div class="sphinxsidebar" role="navigation" aria-label="main navigation">

  418.         <div class="sphinxsidebarwrapper">

  419.   <div>

  420.     <h3><a href="../contents.html">Table of Contents</a></h3>

  421.     <ul>

  422. <li><a class="reference internal" href="#">Developing with asyncio</a><ul>

  423. <li><a class="reference internal" href="#debug-mode">Debug Mode</a></li>

  424. <li><a class="reference internal" href="#concurrency-and-multithreading">Concurrency and Multithreading</a></li>

  425. <li><a class="reference internal" href="#running-blocking-code">Running Blocking Code</a></li>

  426. <li><a class="reference internal" href="#logging">Logging</a></li>

  427. <li><a class="reference internal" href="#detect-never-awaited-coroutines">Detect never-awaited coroutines</a></li>

  428. <li><a class="reference internal" href="#detect-never-retrieved-exceptions">Detect never-retrieved exceptions</a></li>

  429. </ul>

  430. </li>

  431. </ul>

  432. 

  433.   </div>

  434.   <div>

  435.     <h4>Previous topic</h4>

  436.     <p class="topless"><a href="asyncio-llapi-index.html"

  437.                           title="previous chapter">Low-level API Index</a></p>

  438.   </div>

  439.   <div>

  440.     <h4>Next topic</h4>

  441.     <p class="topless"><a href="socket.html"

  442.                           title="next chapter"><code class="xref py py-mod docutils literal notranslate"><span class="pre">socket</span></code> — Low-level networking interface</a></p>

  443.   </div>

  444.   <div role="note" aria-label="source link">

  445.     <h3>This Page</h3>

  446.     <ul class="this-page-menu">

  447.       <li><a href="../bugs.html">Report a Bug</a></li>

  448.       <li>

  449.         <a href="https://github.com/python/cpython/blob/main/Doc/library/asyncio-dev.rst"

  450.             rel="nofollow">Show Source

  451.         </a>

  452.       </li>

  453.     </ul>

  454.   </div>

  455.         </div>

  456. <div id="sidebarbutton" title="Collapse sidebar">

  457. <span>«</span>

  458. </div>

  459. 

  460.       </div>

  461.       <div class="clearer"></div>

  462.     </div>  

  463.     <div class="related" role="navigation" aria-label="related navigation">

  464.       <h3>Navigation</h3>

  465.       <ul>

  466.         <li class="right" style="margin-right: 10px">

  467.           <a href="../genindex.html" title="General Index"

  468.              >index</a></li>

  469.         <li class="right" >

  470.           <a href="../py-modindex.html" title="Python Module Index"

  471.              >modules</a> |</li>

  472.         <li class="right" >

  473.           <a href="socket.html" title="socket — Low-level networking interface"

  474.              >next</a> |</li>

  475.         <li class="right" >

  476.           <a href="asyncio-llapi-index.html" title="Low-level API Index"

  477.              >previous</a> |</li>

  478. 

  479.           <li><img src="../_static/py.svg" alt="Python logo" style="vertical-align: middle; margin-top: -1px"/></li>

  480.           <li><a href="https://www.python.org/">Python</a> &#187;</li>

  481.           <li class="switchers">

  482.             <div class="language_switcher_placeholder"></div>

  483.             <div class="version_switcher_placeholder"></div>

  484.           </li>

  485.           <li>

  486.               

  487.           </li>

  488.     <li id="cpython-language-and-version">

  489.       <a href="../index.html">3.12.3 Documentation</a> &#187;

  490.     </li>

  491. 

  492.           <li class="nav-item nav-item-1"><a href="index.html" >The Python Standard Library</a> &#187;</li>

  493.           <li class="nav-item nav-item-2"><a href="ipc.html" >Networking and Interprocess Communication</a> &#187;</li>

  494.           <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> &#187;</li>

  495.         <li class="nav-item nav-item-this"><a href="">Developing with asyncio</a></li>

  496.                 <li class="right">

  497.                     

  498. 

  499.     <div class="inline-search" role="search">

  500.         <form class="inline-search" action="../search.html" method="get">

  501.           <input placeholder="Quick search" aria-label="Quick search" type="search" name="q" id="search-box" />

  502.           <input type="submit" value="Go" />

  503.         </form>

  504.     </div>

  505.                      |

  506.                 </li>

  507.             <li class="right">

  508. <label class="theme-selector-label">

  509.     Theme

  510.     <select class="theme-selector" oninput="activateTheme(this.value)">

  511.         <option value="auto" selected>Auto</option>

  512.         <option value="light">Light</option>

  513.         <option value="dark">Dark</option>

  514.     </select>

  515. </label> |</li>

  516.             

  517.       </ul>

  518.     </div>  

  519.     <div class="footer">

  520.     &copy; 

  521.       <a href="../copyright.html">

  522.     

  523.     Copyright

  524.     

  525.       </a>

  526.      2001-2024, Python Software Foundation.

  527.     <br />

  528.     This page is licensed under the Python Software Foundation License Version 2.

  529.     <br />

  530.     Examples, recipes, and other code in the documentation are additionally licensed under the Zero Clause BSD License.

  531.     <br />

  532.     

  533.       See <a href="/license.html">History and License</a> for more information.<br />

  534.     

  535.     

  536.     <br />

  537. 

  538.     The Python Software Foundation is a non-profit corporation.

  539. <a href="https://www.python.org/psf/donations/">Please donate.</a>

  540. <br />

  541.     <br />

  542.       Last updated on Apr 09, 2024 (13:47 UTC).

  543.     

  544.       <a href="/bugs.html">Found a bug</a>?

  545.     

  546.     <br />

  547. 

  548.     Created using <a href="https://www.sphinx-doc.org/">Sphinx</a> 7.2.6.

  549.     </div>

  550. 

  551.   </body>

  552. </html>
上海开阖软件有限公司 沪ICP备12045867号-1