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diff --git a/Doc/library/asyncio-future.rst b/Doc/library/asyncio-future.rst deleted file mode 100644 index 832d581..0000000 --- a/Doc/library/asyncio-future.rst +++ /dev/null @@ -1,257 +0,0 @@ -.. currentmodule:: asyncio - - -.. _asyncio-futures: - -======= -Futures -======= - -**Source code:** :source:`Lib/asyncio/futures.py`, -:source:`Lib/asyncio/base_futures.py` - -------------------------------------- - -*Future* objects are used to bridge **low-level callback-based code** -with high-level async/await code. - - -Future Functions -================ - -.. function:: isfuture(obj) - - Return ``True`` if *obj* is either of: - - * an instance of :class:`asyncio.Future`, - * an instance of :class:`asyncio.Task`, - * a Future-like object with a ``_asyncio_future_blocking`` - attribute. - - .. versionadded:: 3.5 - - -.. function:: ensure_future(obj, \*, loop=None) - - Return: - - * *obj* argument as is, if *obj* is a :class:`Future`, - a :class:`Task`, or a Future-like object (:func:`isfuture` - is used for the test.) - - * a :class:`Task` object wrapping *obj*, if *obj* is a - coroutine (:func:`iscoroutine` is used for the test); - in this case the coroutine will be scheduled by - ``ensure_future()``. - - * a :class:`Task` object that would await on *obj*, if *obj* is an - awaitable (:func:`inspect.isawaitable` is used for the test.) - - If *obj* is neither of the above a :exc:`TypeError` is raised. - - .. important:: - - See also the :func:`create_task` function which is the - preferred way for creating new Tasks. - - .. versionchanged:: 3.5.1 - The function accepts any :term:`awaitable` object. - - -.. function:: wrap_future(future, \*, loop=None) - - Wrap a :class:`concurrent.futures.Future` object in a - :class:`asyncio.Future` object. - - -Future Object -============= - -.. class:: Future(\*, loop=None) - - A Future represents an eventual result of an asynchronous - operation. Not thread-safe. - - Future is an :term:`awaitable` object. Coroutines can await on - Future objects until they either have a result or an exception - set, or until they are cancelled. - - Typically Futures are used to enable low-level - callback-based code (e.g. in protocols implemented using asyncio - :ref:`transports <asyncio-transports-protocols>`) - to interoperate with high-level async/await code. - - 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 - :meth:`loop.create_future`. This way alternative event loop - implementations can inject their own optimized implementations - of a Future object. - - .. versionchanged:: 3.7 - Added support for the :mod:`contextvars` module. - - .. method:: result() - - Return the result of the Future. - - If the Future is *done* and has a result set by the - :meth:`set_result` method, the result value is returned. - - If the Future is *done* and has an exception set by the - :meth:`set_exception` method, this method raises the exception. - - If the Future has been *cancelled*, this method raises - a :exc:`CancelledError` exception. - - If the Future's result isn't yet available, this method raises - a :exc:`InvalidStateError` exception. - - .. method:: set_result(result) - - Mark the Future as *done* and set its result. - - Raises a :exc:`InvalidStateError` error if the Future is - already *done*. - - .. method:: set_exception(exception) - - Mark the Future as *done* and set an exception. - - Raises a :exc:`InvalidStateError` error if the Future is - already *done*. - - .. method:: done() - - Return ``True`` if the Future is *done*. - - A Future is *done* if it was *cancelled* or if it has a result - or an exception set with :meth:`set_result` or - :meth:`set_exception` calls. - - .. method:: cancelled() - - Return ``True`` if the Future was *cancelled*. - - The method is usually used to check if a Future is not - *cancelled* before setting a result or an exception for it:: - - if not fut.cancelled(): - fut.set_result(42) - - .. method:: add_done_callback(callback, *, context=None) - - Add a callback to be run when the Future is *done*. - - The *callback* is called with the Future object as its only - argument. - - If the Future is already *done* when this method is called, - the callback is scheduled with :meth:`loop.call_soon`. - - An optional keyword-only *context* argument allows specifying a - custom :class:`contextvars.Context` for the *callback* to run in. - The current context is used when no *context* is provided. - - :func:`functools.partial` can be used to pass parameters - to the callback, e.g.:: - - # Call 'print("Future:", fut)' when "fut" is done. - fut.add_done_callback( - functools.partial(print, "Future:")) - - .. versionchanged:: 3.7 - The *context* keyword-only parameter was added. - See :pep:`567` for more details. - - .. method:: remove_done_callback(callback) - - Remove *callback* from the callbacks list. - - Returns the number of callbacks removed, which is typically 1, - unless a callback was added more than once. - - .. method:: cancel() - - Cancel the Future and schedule callbacks. - - If the Future is already *done* or *cancelled*, return ``False``. - Otherwise, change the Future's state to *cancelled*, - schedule the callbacks, and return ``True``. - - .. method:: exception() - - Return the exception that was set on this Future. - - The exception (or ``None`` if no exception was set) is - returned only if the Future is *done*. - - If the Future has been *cancelled*, this method raises a - :exc:`CancelledError` exception. - - If the Future isn't *done* yet, this method raises an - :exc:`InvalidStateError` exception. - - .. method:: get_loop() - - Return the event loop the Future object is bound to. - - .. versionadded:: 3.7 - - -.. _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:: - - async def set_after(fut, delay, value): - # Sleep for *delay* seconds. - await asyncio.sleep(delay) - - # Set *value* as a result of *fut* Future. - fut.set_result(value) - - async def main(): - # Get the current event loop. - loop = asyncio.get_running_loop() - - # Create a new Future object. - fut = loop.create_future() - - # Run "set_after()" coroutine in a parallel Task. - # We are using the low-level "loop.create_task()" API here because - # we already have a reference to the event loop at hand. - # Otherwise we could have just used "asyncio.create_task()". - loop.create_task( - set_after(fut, 1, '... world')) - - print('hello ...') - - # Wait until *fut* has a result (1 second) and print it. - print(await fut) - - asyncio.run(main()) - - -.. important:: - - The Future object was designed to mimic - :class:`concurrent.futures.Future`. Key differences include: - - - unlike asyncio Futures, :class:`concurrent.futures.Future` - instances cannot be awaited. - - - :meth:`asyncio.Future.result` and :meth:`asyncio.Future.exception` - do not accept the *timeout* argument. - - - :meth:`asyncio.Future.result` and :meth:`asyncio.Future.exception` - raise an :exc:`InvalidStateError` exception when the Future is not - *done*. - - - Callbacks registered with :meth:`asyncio.Future.add_done_callback` - are not called immediately. They are scheduled with - :meth:`loop.call_soon` instead. - - - asyncio Future is not compatible with the - :func:`concurrent.futures.wait` and - :func:`concurrent.futures.as_completed` functions. |