asyncio doc: explain how to pass keywords to callbacks (functools.partial)
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@ -67,10 +67,22 @@ Run an event loop
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This is idempotent and irreversible. No other methods should be called after
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this one.
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.. _asyncio-pass-keywords:
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Calls
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-----
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Most :mod:`asyncio` functions don't accept keywords. If you want to pass
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keywords to your callback, use :func:`functools.partial`. For example,
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``loop.call_soon(functools.partial(print, "Hello", flush=True))`` will call
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``print("Hello", flush=True)``.
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.. note::
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:func:`functools.partial` is better than ``lambda`` functions, because
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:mod:`asyncio` can inspect :func:`functools.partial` object to display
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parameters in debug mode, whereas ``lambda`` functions have a poor
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representation.
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.. method:: BaseEventLoop.call_soon(callback, \*args)
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Arrange for a callback to be called as soon as possible.
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@ -83,6 +95,9 @@ Calls
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An instance of :class:`asyncio.Handle` is returned.
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:ref:`Use functools.partial to pass keywords to the callback
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<asyncio-pass-keywords>`.
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.. method:: BaseEventLoop.call_soon_threadsafe(callback, \*args)
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Like :meth:`call_soon`, but thread safe.
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@ -118,6 +133,9 @@ a different clock than :func:`time.time`.
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is called. If you want the callback to be called with some named
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arguments, use a closure or :func:`functools.partial`.
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:ref:`Use functools.partial to pass keywords to the callback
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<asyncio-pass-keywords>`.
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.. method:: BaseEventLoop.call_at(when, callback, *args)
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Arrange for the *callback* to be called at the given absolute timestamp
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@ -126,6 +144,9 @@ a different clock than :func:`time.time`.
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This method's behavior is the same as :meth:`call_later`.
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:ref:`Use functools.partial to pass keywords to the callback
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<asyncio-pass-keywords>`.
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.. method:: BaseEventLoop.time()
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Return the current time, as a :class:`float` value, according to the
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@ -334,6 +355,9 @@ On Windows with :class:`ProactorEventLoop`, these methods are not supported.
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Start watching the file descriptor for read availability and then call the
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*callback* with specified arguments.
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:ref:`Use functools.partial to pass keywords to the callback
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<asyncio-pass-keywords>`.
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.. method:: BaseEventLoop.remove_reader(fd)
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Stop watching the file descriptor for read availability.
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@ -343,6 +367,9 @@ On Windows with :class:`ProactorEventLoop`, these methods are not supported.
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Start watching the file descriptor for write availability and then call the
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*callback* with specified arguments.
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:ref:`Use functools.partial to pass keywords to the callback
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<asyncio-pass-keywords>`.
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.. method:: BaseEventLoop.remove_writer(fd)
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Stop watching the file descriptor for write availability.
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@ -493,6 +520,9 @@ Availability: UNIX only.
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Raise :exc:`ValueError` if the signal number is invalid or uncatchable.
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Raise :exc:`RuntimeError` if there is a problem setting up the handler.
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:ref:`Use functools.partial to pass keywords to the callback
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<asyncio-pass-keywords>`.
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.. method:: BaseEventLoop.remove_signal_handler(sig)
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Remove a handler for a signal.
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@ -518,6 +548,9 @@ pool of processes). By default, an event loop uses a thread pool executor
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The *executor* argument should be an :class:`~concurrent.futures.Executor`
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instance. The default executor is used if *executor* is ``None``.
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:ref:`Use functools.partial to pass keywords to the callback
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<asyncio-pass-keywords>`.
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This method is a :ref:`coroutine <coroutine>`.
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.. method:: BaseEventLoop.set_default_executor(executor)
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@ -253,6 +253,11 @@ Future
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future is already done when this is called, the callback is scheduled
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with :meth:`~BaseEventLoop.call_soon`.
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:ref:`Use functools.partial to pass parameters to the callback
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<asyncio-pass-keywords>`. For example,
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``fut.add_done_callback(functools.partial(print, "Future:",
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flush=True))`` will call ``print("Future:", fut, flush=True)``.
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.. method:: remove_done_callback(fn)
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Remove all instances of a callback from the "call when done" list.
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