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  194.   <section id="futures">

  195. <span id="asyncio-futures"></span><h1>Futures<a class="headerlink" href="#futures" title="Link to this heading">¶</a></h1>

  196. <p><strong>Source code:</strong> <a class="reference external" href="https://github.com/python/cpython/tree/3.12/Lib/asyncio/futures.py">Lib/asyncio/futures.py</a>,

  197. <a class="reference external" href="https://github.com/python/cpython/tree/3.12/Lib/asyncio/base_futures.py">Lib/asyncio/base_futures.py</a></p>

  198. <hr class="docutils" />

  199. <p><em>Future</em> objects are used to bridge <strong>low-level callback-based code</strong>

  200. with high-level async/await code.</p>

  201. <section id="future-functions">

  202. <h2>Future Functions<a class="headerlink" href="#future-functions" title="Link to this heading">¶</a></h2>

  203. <dl class="py function">

  204. <dt class="sig sig-object py" id="asyncio.isfuture">

  205. <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>

  206. <dd><p>Return <code class="docutils literal notranslate"><span class="pre">True</span></code> if <em>obj</em> is either of:</p>

  207. <ul class="simple">

  208. <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>

  209. <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>

  210. <li><p>a Future-like object with a <code class="docutils literal notranslate"><span class="pre">_asyncio_future_blocking</span></code>

  211. attribute.</p></li>

  212. </ul>

  213. <div class="versionadded">

  214. <p><span class="versionmodified added">New in version 3.5.</span></p>

  215. </div>

  216. </dd></dl>

  217. 

  218. <dl class="py function">

  219. <dt class="sig sig-object py" id="asyncio.ensure_future">

  220. <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="o"><span class="pre">*</span></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>

  221. <dd><p>Return:</p>

  222. <ul class="simple">

  223. <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>,

  224. 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>

  225. is used for the test.)</p></li>

  226. <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

  227. 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);

  228. in this case the coroutine will be scheduled by

  229. <code class="docutils literal notranslate"><span class="pre">ensure_future()</span></code>.</p></li>

  230. <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

  231. 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>

  232. </ul>

  233. <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>

  234. <div class="admonition important">

  235. <p class="admonition-title">Important</p>

  236. <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

  237. preferred way for creating new Tasks.</p>

  238. <p>Save a reference to the result of this function, to avoid

  239. a task disappearing mid-execution.</p>

  240. </div>

  241. <div class="versionchanged">

  242. <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>

  243. </div>

  244. <div class="deprecated">

  245. <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

  246. and <em>loop</em> is not specified and there is no running event loop.</p>

  247. </div>

  248. </dd></dl>

  249. 

  250. <dl class="py function">

  251. <dt class="sig sig-object py" id="asyncio.wrap_future">

  252. <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="o"><span class="pre">*</span></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>

  253. <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

  254. <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>

  255. <div class="deprecated">

  256. <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

  257. and <em>loop</em> is not specified and there is no running event loop.</p>

  258. </div>

  259. </dd></dl>

  260. 

  261. </section>

  262. <section id="future-object">

  263. <h2>Future Object<a class="headerlink" href="#future-object" title="Link to this heading">¶</a></h2>

  264. <dl class="py class">

  265. <dt class="sig sig-object py" id="asyncio.Future">

  266. <em class="property"><span class="pre">class</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="o"><span class="pre">*</span></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>

  267. <dd><p>A Future represents an eventual result of an asynchronous

  268. operation.  Not thread-safe.</p>

  269. <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

  270. Future objects until they either have a result or an exception

  271. set, or until they are cancelled. A Future can be awaited multiple

  272. times and the result is same.</p>

  273. <p>Typically Futures are used to enable low-level

  274. callback-based code (e.g. in protocols implemented using asyncio

  275. <a class="reference internal" href="asyncio-protocol.html#asyncio-transports-protocols"><span class="std std-ref">transports</span></a>)

  276. to interoperate with high-level async/await code.</p>

  277. <p>The rule of thumb is to never expose Future objects in user-facing

  278. APIs, and the recommended way to create a Future object is to call

  279. <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

  280. implementations can inject their own optimized implementations

  281. of a Future object.</p>

  282. <div class="versionchanged">

  283. <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>

  284. </div>

  285. <div class="deprecated">

  286. <p><span class="versionmodified deprecated">Deprecated since version 3.10: </span>Deprecation warning is emitted if <em>loop</em> is not specified

  287. and there is no running event loop.</p>

  288. </div>

  289. <dl class="py method">

  290. <dt class="sig sig-object py" id="asyncio.Future.result">

  291. <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>

  292. <dd><p>Return the result of the Future.</p>

  293. <p>If the Future is <em>done</em> and has a result set by the

  294. <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>

  295. <p>If the Future is <em>done</em> and has an exception set by the

  296. <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>

  297. <p>If the Future has been <em>cancelled</em>, this method raises

  298. 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>

  299. <p>If the Future’s result isn’t yet available, this method raises

  300. a <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>

  301. </dd></dl>

  302. 

  303. <dl class="py method">

  304. <dt class="sig sig-object py" id="asyncio.Future.set_result">

  305. <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>

  306. <dd><p>Mark the Future as <em>done</em> and set its result.</p>

  307. <p>Raises a <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

  308. already <em>done</em>.</p>

  309. </dd></dl>

  310. 

  311. <dl class="py method">

  312. <dt class="sig sig-object py" id="asyncio.Future.set_exception">

  313. <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>

  314. <dd><p>Mark the Future as <em>done</em> and set an exception.</p>

  315. <p>Raises a <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

  316. already <em>done</em>.</p>

  317. </dd></dl>

  318. 

  319. <dl class="py method">

  320. <dt class="sig sig-object py" id="asyncio.Future.done">

  321. <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>

  322. <dd><p>Return <code class="docutils literal notranslate"><span class="pre">True</span></code> if the Future is <em>done</em>.</p>

  323. <p>A Future is <em>done</em> if it was <em>cancelled</em> or if it has a result

  324. 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

  325. <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>

  326. </dd></dl>

  327. 

  328. <dl class="py method">

  329. <dt class="sig sig-object py" id="asyncio.Future.cancelled">

  330. <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>

  331. <dd><p>Return <code class="docutils literal notranslate"><span class="pre">True</span></code> if the Future was <em>cancelled</em>.</p>

  332. <p>The method is usually used to check if a Future is not

  333. <em>cancelled</em> before setting a result or an exception for it:</p>

  334. <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>

  335.     <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>

  336. </pre></div>

  337. </div>

  338. </dd></dl>

  339. 

  340. <dl class="py method">

  341. <dt class="sig sig-object py" id="asyncio.Future.add_done_callback">

  342. <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="o"><span class="pre">*</span></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>

  343. <dd><p>Add a callback to be run when the Future is <em>done</em>.</p>

  344. <p>The <em>callback</em> is called with the Future object as its only

  345. argument.</p>

  346. <p>If the Future is already <em>done</em> when this method is called,

  347. 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>

  348. <p>An optional keyword-only <em>context</em> argument allows specifying a

  349. 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.

  350. The current context is used when no <em>context</em> is provided.</p>

  351. <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

  352. to the callback, e.g.:</p>

  353. <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="c1"># Call &#39;print(&quot;Future:&quot;, fut)&#39; when &quot;fut&quot; is done.</span>

  354. <span class="n">fut</span><span class="o">.</span><span class="n">add_done_callback</span><span class="p">(</span>

  355.     <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">&quot;Future:&quot;</span><span class="p">))</span>

  356. </pre></div>

  357. </div>

  358. <div class="versionchanged">

  359. <p><span class="versionmodified changed">Changed in version 3.7: </span>The <em>context</em> keyword-only parameter was added.

  360. 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>

  361. </div>

  362. </dd></dl>

  363. 

  364. <dl class="py method">

  365. <dt class="sig sig-object py" id="asyncio.Future.remove_done_callback">

  366. <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>

  367. <dd><p>Remove <em>callback</em> from the callbacks list.</p>

  368. <p>Returns the number of callbacks removed, which is typically 1,

  369. unless a callback was added more than once.</p>

  370. </dd></dl>

  371. 

  372. <dl class="py method">

  373. <dt class="sig sig-object py" id="asyncio.Future.cancel">

  374. <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>

  375. <dd><p>Cancel the Future and schedule callbacks.</p>

  376. <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>.

  377. Otherwise, change the Future’s state to <em>cancelled</em>,

  378. schedule the callbacks, and return <code class="docutils literal notranslate"><span class="pre">True</span></code>.</p>

  379. <div class="versionchanged">

  380. <p><span class="versionmodified changed">Changed in version 3.9: </span>Added the <em>msg</em> parameter.</p>

  381. </div>

  382. </dd></dl>

  383. 

  384. <dl class="py method">

  385. <dt class="sig sig-object py" id="asyncio.Future.exception">

  386. <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>

  387. <dd><p>Return the exception that was set on this Future.</p>

  388. <p>The exception (or <code class="docutils literal notranslate"><span class="pre">None</span></code> if no exception was set) is

  389. returned only if the Future is <em>done</em>.</p>

  390. <p>If the Future has been <em>cancelled</em>, this method raises a

  391. <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>

  392. <p>If the Future isn’t <em>done</em> yet, this method raises an

  393. <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>

  394. </dd></dl>

  395. 

  396. <dl class="py method">

  397. <dt class="sig sig-object py" id="asyncio.Future.get_loop">

  398. <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>

  399. <dd><p>Return the event loop the Future object is bound to.</p>

  400. <div class="versionadded">

  401. <p><span class="versionmodified added">New in version 3.7.</span></p>

  402. </div>

  403. </dd></dl>

  404. 

  405. </dd></dl>

  406. 

  407. <p id="asyncio-example-future">This example creates a Future object, creates and schedules an

  408. asynchronous Task to set result for the Future, and waits until

  409. the Future has a result:</p>

  410. <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">async</span> <span class="k">def</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>

  411.     <span class="c1"># Sleep for *delay* seconds.</span>

  412.     <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>

  413. 

  414.     <span class="c1"># Set *value* as a result of *fut* Future.</span>

  415.     <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>

  416. 

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

  418.     <span class="c1"># Get the current event loop.</span>

  419.     <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>

  420. 

  421.     <span class="c1"># Create a new Future object.</span>

  422.     <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>

  423. 

  424.     <span class="c1"># Run &quot;set_after()&quot; coroutine in a parallel Task.</span>

  425.     <span class="c1"># We are using the low-level &quot;loop.create_task()&quot; API here because</span>

  426.     <span class="c1"># we already have a reference to the event loop at hand.</span>

  427.     <span class="c1"># Otherwise we could have just used &quot;asyncio.create_task()&quot;.</span>

  428.     <span class="n">loop</span><span class="o">.</span><span class="n">create_task</span><span class="p">(</span>

  429.         <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">&#39;... world&#39;</span><span class="p">))</span>

  430. 

  431.     <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;hello ...&#39;</span><span class="p">)</span>

  432. 

  433.     <span class="c1"># Wait until *fut* has a result (1 second) and print it.</span>

  434.     <span class="nb">print</span><span class="p">(</span><span class="k">await</span> <span class="n">fut</span><span class="p">)</span>

  435. 

  436. <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>

  437. </pre></div>

  438. </div>

  439. <div class="admonition important">

  440. <p class="admonition-title">Important</p>

  441. <p>The Future object was designed to mimic

  442. <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>

  443. <ul class="simple">

  444. <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>

  445. instances cannot be awaited.</p></li>

  446. <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>

  447. do not accept the <em>timeout</em> argument.</p></li>

  448. <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>

  449. 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

  450. <em>done</em>.</p></li>

  451. <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>

  452. are not called immediately.  They are scheduled with

  453. <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>

  454. <li><p>asyncio Future is not compatible with the

  455. <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

  456. <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>

  457. <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,

  458. 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>

  459. </ul>

  460. </div>

  461. </section>

  462. </section>

  463. 

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  475. <li><a class="reference internal" href="#future-functions">Future Functions</a></li>

  476. <li><a class="reference internal" href="#future-object">Future Object</a></li>

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