bpo-33649: Edit asyncio eventloop doc - second pass (GH-9233)
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Carol Willing
Yury Selivanov
parent
e1a34ceb54
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5b7cbd602e
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@ -8,18 +8,18 @@ Event Loop
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.. rubric:: Preface
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An event loop is the central component of every asyncio application.
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The event loop is a central component of every asyncio application.
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Event loops run asynchronous tasks and callbacks, perform network
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IO operations, run subprocesses, etc.
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IO operations, and run subprocesses.
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In general, it is *not recommended* to use event loops directly at
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the application-level asyncio code. They should only be accessed
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in low-level code in libraries and frameworks.
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High-level asyncio applications should not need to work with event
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loops and should use the :func:`asyncio.run` function to initialize
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and run asynchronous code.
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Application developers will typically use high-level asyncio functions
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to interact with the event loop. In general, high-level asyncio applications
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should not need to work directly with event loops and, instead, should use
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the :func:`asyncio.run` function to initialize, manage the event loop, and
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run asynchronous code.
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Alternatively, developers of low-level code, such as libraries and
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framework, may need access to the event loop.
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.. rubric:: Accessing Event Loop
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@ -42,13 +42,13 @@ an event loop:
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been called, asyncio will create a new event loop and set it as the
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current one.
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Because this function has a rather complex behavior (especially
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when custom event loop policies are in use), it is recommended
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to use the :func:`get_running_loop` function in coroutines and
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callbacks instead.
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Because this function has rather complex behavior (especially
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when custom event loop policies are in use), using the
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:func:`get_running_loop` function is preferred to :func:`get_event_loop`
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in coroutines and callbacks.
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Consider also using the :func:`asyncio.run` function instead of
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manually creating and closing an event loop.
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Consider also using the :func:`asyncio.run` function instead of using
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lower level functions to manually create and close an event loop.
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.. function:: set_event_loop(loop)
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@ -67,14 +67,14 @@ and :func:`new_event_loop` functions can be altered by
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This documentation page contains the following sections:
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* The `Event Loop Methods`_ section is a reference documentation of
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* The `Event Loop Methods`_ section is the reference documentation of
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event loop APIs;
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* The `Callback Handles`_ section documents the :class:`Handle` and
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:class:`TimerHandle`, instances of which are returned from functions
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:meth:`loop.call_soon`, :meth:`loop.call_later`, etc;
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:class:`TimerHandle`, instances which are returned from functions, such
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as :meth:`loop.call_soon` and :meth:`loop.call_later`;
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* The `Server Objects`_ sections documents types returned from
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* The `Server Objects`_ sections document types returned from
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event loop methods like :meth:`loop.create_server`;
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* The `Event Loops Implementations`_ section documents the
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@ -89,7 +89,7 @@ This documentation page contains the following sections:
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Event Loop Methods
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==================
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Event loops provide the following **low-level** APIs:
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Event loops have **low-level** APIs for the following:
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.. contents::
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:depth: 1
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@ -120,8 +120,8 @@ Running and stopping the loop
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If :meth:`stop` is called while :meth:`run_forever` is running,
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the loop will run the current batch of callbacks and then exit.
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Note that callbacks scheduled by callbacks will not run in that
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case; they will run the next time :meth:`run_forever` or
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Note that callbacks scheduled by callbacks will not run in this
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case; instead, they will run the next time :meth:`run_forever` or
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:meth:`run_until_complete` is called.
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.. method:: loop.stop()
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@ -140,7 +140,7 @@ Running and stopping the loop
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Close the event loop.
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The loop cannot not be running when this function is called.
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The loop must be running when this function is called.
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Any pending callbacks will be discarded.
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This method clears all queues and shuts down the executor, but does
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@ -154,8 +154,9 @@ Running and stopping the loop
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Schedule all currently open :term:`asynchronous generator` objects to
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close with an :meth:`~agen.aclose()` call. After calling this method,
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the event loop will issue a warning if a new asynchronous generator
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is iterated. Should be used to reliably finalize all scheduled
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asynchronous generators, e.g.:
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is iterated. This should be used to reliably finalize all scheduled
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asynchronous generators, e.g.::
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try:
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loop.run_forever()
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@ -173,7 +174,7 @@ Scheduling callbacks
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.. method:: loop.call_soon(callback, *args, context=None)
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Schedule *callback* to be called with *args* arguments at
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Schedule a *callback* to be called with *args* arguments at
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the next iteration of the event loop.
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Callbacks are called in the order in which they are registered.
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@ -184,7 +185,9 @@ Scheduling callbacks
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The current context is used when no *context* is provided.
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An instance of :class:`asyncio.Handle` is returned, which can be
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used to cancel the callback.
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used later to cancel the callback.
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This method is not thread-safe.
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.. method:: loop.call_soon_threadsafe(callback, *args, context=None)
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@ -200,11 +203,11 @@ Scheduling callbacks
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.. note::
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Most :mod:`asyncio` scheduling functions don't allow to pass
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Most :mod:`asyncio` scheduling functions don't allow passing
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keyword arguments. To do that, use :func:`functools.partial`,
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e.g.::
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# will schedule "print("Hello", flush=True)":
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# will schedule "print("Hello", flush=True)"
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loop.call_soon(
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functools.partial(print, "Hello", flush=True))
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@ -232,7 +235,7 @@ clocks to track time.
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be used to cancel the callback.
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*callback* will be called exactly once. If two callbacks are
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scheduled for exactly the same time, it is undefined which will
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scheduled for exactly the same time, it is undefined which one will
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be called first.
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The optional positional *args* will be passed to the callback when
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@ -284,8 +287,8 @@ Creating Futures and Tasks
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Create an :class:`asyncio.Future` object attached to the event loop.
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This is the preferred way to create Futures in asyncio, that lets
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third-party event loops to provide alternative implementations of
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This is the preferred way to create Futures in asyncio. This lets
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third-party event loops provide alternative implementations of
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the Future object (with better performance or instrumentation).
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.. versionadded:: 3.5.2
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@ -397,7 +400,7 @@ Opening network connections
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* *local_addr*, if given, is a ``(local_host, local_port)`` tuple used
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to bind the socket to locally. The *local_host* and *local_port*
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are looked up using getaddrinfo(), similarly to *host* and *port*.
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are looked up using ``getaddrinfo()``, similarly to *host* and *port*.
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* *ssl_handshake_timeout* is (for an SSL connection) the time in seconds
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to wait for the SSL handshake to complete before aborting the connection.
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@ -532,16 +535,17 @@ Creating network servers
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Arguments:
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* The *host* parameter can be a string, in that case the TCP server is
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bound to *host* and *port*. The *host* parameter can also be a sequence
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of strings and in that case the TCP server is bound to all hosts of the
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sequence. If *host* is an empty string or ``None``, all interfaces are
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assumed and a list of multiple sockets will be returned (most likely one
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for IPv4 and another one for IPv6).
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* The *host* parameter can be set to several types which determine behavior:
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- If *host* is a string, the TCP server is bound to *host* and *port*.
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- if *host* is a sequence of strings, the TCP server is bound to all
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hosts of the sequence.
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- If *host* is an empty string or ``None``, all interfaces are
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assumed and a list of multiple sockets will be returned (most likely
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one for IPv4 and another one for IPv6).
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* *family* can be set to either :data:`socket.AF_INET` or
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:data:`~socket.AF_INET6` to force the socket to use IPv4 or IPv6.
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If not set it will be determined from host name
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If not set, the *family* will be determined from host name
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(defaults to :data:`~socket.AF_UNSPEC`).
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* *flags* is a bitmask for :meth:`getaddrinfo`.
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@ -721,16 +725,16 @@ Watching file descriptors
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.. method:: loop.add_reader(fd, callback, \*args)
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Start watching the file descriptor for read availability and
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Start watching the file descriptor *fd* for read availability and
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call the *callback* with specified arguments.
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.. method:: loop.remove_reader(fd)
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Stop watching the file descriptor for read availability.
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Stop watching the file descriptor *fd* for read availability.
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.. method:: loop.add_writer(fd, callback, \*args)
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Start watching the file descriptor for write availability and then
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Start watching the file descriptor *fd* for write availability and then
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call the *callback* with specified arguments.
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Use :func:`functools.partial` :ref:`to pass keywords
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@ -738,7 +742,7 @@ Watching file descriptors
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.. method:: loop.remove_writer(fd)
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Stop watching the file descriptor for write availability.
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Stop watching the file descriptor *fd* for write availability.
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See also :ref:`Platform Support <asyncio-platform-support>` section
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for some limitations of these methods.
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@ -747,10 +751,10 @@ for some limitations of these methods.
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Working with socket objects directly
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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In general, protocols implementations that use transport-based APIs
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In general, protocol implementations that use transport-based APIs
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such as :meth:`loop.create_connection` and :meth:`loop.create_server`
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are faster than implementations that work with sockets directly.
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However, there are use cases when performance is not critical and
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However, there are some use cases when performance is not critical, and
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working with :class:`~socket.socket` objects directly is more
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convenient.
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@ -765,8 +769,8 @@ convenient.
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The socket *sock* must be non-blocking.
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.. versionchanged:: 3.7
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Even though the method was always documented as a coroutine
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method, before Python 3.7 it returned a :class:`Future`.
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Even though this method was always documented as a coroutine
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method, releases before Python 3.7 returned a :class:`Future`.
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Since Python 3.7 this is an ``async def`` method.
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.. coroutinemethod:: loop.sock_recv_into(sock, buf)
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@ -785,10 +789,11 @@ convenient.
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Send data to the socket. Asynchronous version of
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:meth:`socket.sendall() <socket.socket.sendall>`.
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This method continues to send data from *data* until either all data has
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been sent or an error occurs. ``None`` is returned on success. On error,
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an exception is raised, and there is no way to determine how much data, if
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any, was successfully processed by the receiving end of the connection.
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This method continues to send data from *data* to the socket until either
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all data in *data* has been sent or an error occurs. ``None`` is returned
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on success. On error, an exception is raised. Additionally, there is no way
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to determine how much data, if any, was successfully processed by the
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receiving end of the connection.
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The socket *sock* must be non-blocking.
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@ -860,7 +865,7 @@ convenient.
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<io.IOBase.tell>` can be used to figure out the number of bytes
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which were sent.
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*fallback* set to ``True`` makes asyncio to manually read and send
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*fallback*, when set to ``True``, makes asyncio manually read and send
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the file when the platform does not support the sendfile syscall
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(e.g. Windows or SSL socket on Unix).
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@ -927,7 +932,7 @@ Working with pipes
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.. note::
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:class:`SelectorEventLoop` does not support the above methods on
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Windows. Use :class:`ProactorEventLoop` instead.
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Windows. Use :class:`ProactorEventLoop` instead for Windows.
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.. seealso::
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@ -1028,8 +1033,8 @@ Allows customizing how exceptions are handled in the event loop.
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Default exception handler.
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This is called when an exception occurs and no exception
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handler is set, and can be called by a custom exception
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handler that wants to defer to the default behavior.
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handler is set. This can be called by a custom exception
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handler that wants to defer to the default handler behavior.
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*context* parameter has the same meaning as in
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:meth:`call_exception_handler`.
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@ -1051,7 +1056,7 @@ Allows customizing how exceptions are handled in the event loop.
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.. note::
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Note: this method should not be overloaded in subclassed
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This method should not be overloaded in subclassed
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event loops. For any custom exception handling, use
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:meth:`set_exception_handler()` method.
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@ -1104,7 +1109,7 @@ async/await code consider using high-level convenient
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:ref:`filesystem encoding <filesystem-encoding>`.
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The first string specifies the program to execute,
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and the remaining strings specify the arguments. Together string
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and the remaining strings specify the arguments. Together, string
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arguments form the ``argv`` of the program.
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This is similar to the standard library :class:`subprocess.Popen`
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@ -1238,8 +1243,7 @@ Do not instantiate the class directly.
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async with srv:
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# some code
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# At this point, srv is closed and no longer accepts new
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connections.
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# At this point, srv is closed and no longer accepts new connections.
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.. versionchanged:: 3.7
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@ -1408,6 +1412,7 @@ event loop::
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import asyncio
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def hello_world(loop):
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"""A callback to print 'Hello World' and stop the event loop"""
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print('Hello World')
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loop.stop()
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@ -1478,6 +1483,7 @@ Wait until a file descriptor received some data using the
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# Create a pair of connected file descriptors
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rsock, wsock = socketpair()
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loop = asyncio.get_event_loop()
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def reader():
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@ -1500,7 +1506,7 @@ Wait until a file descriptor received some data using the
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# Run the event loop
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loop.run_forever()
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finally:
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# We are done, close sockets and the event loop
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# We are done. Close sockets and the event loop.
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rsock.close()
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wsock.close()
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loop.close()
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@ -1519,7 +1525,7 @@ Wait until a file descriptor received some data using the
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Set signal handlers for SIGINT and SIGTERM
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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(This example only works on UNIX.)
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(This ``signals`` example only works on UNIX.)
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Register handlers for signals :py:data:`SIGINT` and :py:data:`SIGTERM`
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using the :meth:`loop.add_signal_handler` method::
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