abd1f28bc2
ThreadSafeFlag works on the unix port since commit
df08c38c28.
Signed-off-by: Damien George <damien@micropython.org>
364 lines
9.7 KiB
ReStructuredText
364 lines
9.7 KiB
ReStructuredText
:mod:`asyncio` --- asynchronous I/O scheduler
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=============================================
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.. module:: asyncio
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:synopsis: asynchronous I/O scheduler for writing concurrent code
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|see_cpython_module|
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`asyncio <https://docs.python.org/3.8/library/asyncio.html>`_
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Example::
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import asyncio
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async def blink(led, period_ms):
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while True:
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led.on()
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await asyncio.sleep_ms(5)
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led.off()
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await asyncio.sleep_ms(period_ms)
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async def main(led1, led2):
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asyncio.create_task(blink(led1, 700))
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asyncio.create_task(blink(led2, 400))
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await asyncio.sleep_ms(10_000)
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# Running on a pyboard
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from pyb import LED
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asyncio.run(main(LED(1), LED(2)))
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# Running on a generic board
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from machine import Pin
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asyncio.run(main(Pin(1), Pin(2)))
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Core functions
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--------------
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.. function:: create_task(coro)
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Create a new task from the given coroutine and schedule it to run.
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Returns the corresponding `Task` object.
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.. function:: current_task()
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Return the `Task` object associated with the currently running task.
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.. function:: run(coro)
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Create a new task from the given coroutine and run it until it completes.
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Returns the value returned by *coro*.
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.. function:: sleep(t)
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Sleep for *t* seconds (can be a float).
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This is a coroutine.
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.. function:: sleep_ms(t)
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Sleep for *t* milliseconds.
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This is a coroutine, and a MicroPython extension.
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Additional functions
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--------------------
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.. function:: wait_for(awaitable, timeout)
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Wait for the *awaitable* to complete, but cancel it if it takes longer
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than *timeout* seconds. If *awaitable* is not a task then a task will be
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created from it.
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If a timeout occurs, it cancels the task and raises ``asyncio.TimeoutError``:
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this should be trapped by the caller. The task receives
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``asyncio.CancelledError`` which may be ignored or trapped using ``try...except``
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or ``try...finally`` to run cleanup code.
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Returns the return value of *awaitable*.
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This is a coroutine.
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.. function:: wait_for_ms(awaitable, timeout)
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Similar to `wait_for` but *timeout* is an integer in milliseconds.
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This is a coroutine, and a MicroPython extension.
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.. function:: gather(*awaitables, return_exceptions=False)
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Run all *awaitables* concurrently. Any *awaitables* that are not tasks are
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promoted to tasks.
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Returns a list of return values of all *awaitables*.
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This is a coroutine.
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class Task
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----------
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.. class:: Task()
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This object wraps a coroutine into a running task. Tasks can be waited on
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using ``await task``, which will wait for the task to complete and return
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the return value of the task.
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Tasks should not be created directly, rather use `create_task` to create them.
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.. method:: Task.cancel()
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Cancel the task by injecting ``asyncio.CancelledError`` into it. The task may
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ignore this exception. Cleanup code may be run by trapping it, or via
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``try ... finally``.
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class Event
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-----------
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.. class:: Event()
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Create a new event which can be used to synchronise tasks. Events start
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in the cleared state.
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.. method:: Event.is_set()
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Returns ``True`` if the event is set, ``False`` otherwise.
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.. method:: Event.set()
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Set the event. Any tasks waiting on the event will be scheduled to run.
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Note: This must be called from within a task. It is not safe to call this
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from an IRQ, scheduler callback, or other thread. See `ThreadSafeFlag`.
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.. method:: Event.clear()
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Clear the event.
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.. method:: Event.wait()
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Wait for the event to be set. If the event is already set then it returns
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immediately.
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This is a coroutine.
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class ThreadSafeFlag
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--------------------
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.. class:: ThreadSafeFlag()
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Create a new flag which can be used to synchronise a task with code running
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outside the asyncio loop, such as other threads, IRQs, or scheduler
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callbacks. Flags start in the cleared state.
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.. method:: ThreadSafeFlag.set()
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Set the flag. If there is a task waiting on the flag, it will be scheduled
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to run.
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.. method:: ThreadSafeFlag.clear()
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Clear the flag. This may be used to ensure that a possibly previously-set
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flag is clear before waiting for it.
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.. method:: ThreadSafeFlag.wait()
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Wait for the flag to be set. If the flag is already set then it returns
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immediately. The flag is automatically reset upon return from ``wait``.
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A flag may only be waited on by a single task at a time.
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This is a coroutine.
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class Lock
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----------
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.. class:: Lock()
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Create a new lock which can be used to coordinate tasks. Locks start in
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the unlocked state.
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In addition to the methods below, locks can be used in an ``async with`` statement.
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.. method:: Lock.locked()
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Returns ``True`` if the lock is locked, otherwise ``False``.
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.. method:: Lock.acquire()
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Wait for the lock to be in the unlocked state and then lock it in an atomic
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way. Only one task can acquire the lock at any one time.
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This is a coroutine.
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.. method:: Lock.release()
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Release the lock. If any tasks are waiting on the lock then the next one in the
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queue is scheduled to run and the lock remains locked. Otherwise, no tasks are
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waiting an the lock becomes unlocked.
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TCP stream connections
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----------------------
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.. function:: open_connection(host, port, ssl=None)
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Open a TCP connection to the given *host* and *port*. The *host* address will be
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resolved using `socket.getaddrinfo`, which is currently a blocking call.
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If *ssl* is a `ssl.SSLContext` object, this context is used to create the transport;
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if *ssl* is ``True``, a default context is used.
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Returns a pair of streams: a reader and a writer stream.
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Will raise a socket-specific ``OSError`` if the host could not be resolved or if
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the connection could not be made.
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This is a coroutine.
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.. function:: start_server(callback, host, port, backlog=5, ssl=None)
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Start a TCP server on the given *host* and *port*. The *callback* will be
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called with incoming, accepted connections, and be passed 2 arguments: reader
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and writer streams for the connection.
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If *ssl* is a `ssl.SSLContext` object, this context is used to create the transport.
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Returns a `Server` object.
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This is a coroutine.
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.. class:: Stream()
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This represents a TCP stream connection. To minimise code this class implements
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both a reader and a writer, and both ``StreamReader`` and ``StreamWriter`` alias to
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this class.
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.. method:: Stream.get_extra_info(v)
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Get extra information about the stream, given by *v*. The valid values for *v* are:
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``peername``.
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.. method:: Stream.close()
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Close the stream.
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.. method:: Stream.wait_closed()
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Wait for the stream to close.
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This is a coroutine.
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.. method:: Stream.read(n=-1)
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Read up to *n* bytes and return them. If *n* is not provided or -1 then read all
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bytes until EOF. The returned value will be an empty bytes object if EOF is
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encountered before any bytes are read.
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This is a coroutine.
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.. method:: Stream.readinto(buf)
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Read up to n bytes into *buf* with n being equal to the length of *buf*.
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Return the number of bytes read into *buf*.
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This is a coroutine, and a MicroPython extension.
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.. method:: Stream.readexactly(n)
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Read exactly *n* bytes and return them as a bytes object.
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Raises an ``EOFError`` exception if the stream ends before reading *n* bytes.
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This is a coroutine.
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.. method:: Stream.readline()
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Read a line and return it.
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This is a coroutine.
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.. method:: Stream.write(buf)
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Accumulated *buf* to the output buffer. The data is only flushed when
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`Stream.drain` is called. It is recommended to call `Stream.drain` immediately
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after calling this function.
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.. method:: Stream.drain()
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Drain (write) all buffered output data out to the stream.
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This is a coroutine.
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.. class:: Server()
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This represents the server class returned from `start_server`. It can be used
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in an ``async with`` statement to close the server upon exit.
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.. method:: Server.close()
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Close the server.
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.. method:: Server.wait_closed()
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Wait for the server to close.
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This is a coroutine.
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Event Loop
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----------
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.. function:: get_event_loop()
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Return the event loop used to schedule and run tasks. See `Loop`.
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.. function:: new_event_loop()
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Reset the event loop and return it.
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Note: since MicroPython only has a single event loop this function just
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resets the loop's state, it does not create a new one.
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.. class:: Loop()
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This represents the object which schedules and runs tasks. It cannot be
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created, use `get_event_loop` instead.
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.. method:: Loop.create_task(coro)
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Create a task from the given *coro* and return the new `Task` object.
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.. method:: Loop.run_forever()
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Run the event loop until `stop()` is called.
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.. method:: Loop.run_until_complete(awaitable)
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Run the given *awaitable* until it completes. If *awaitable* is not a task
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then it will be promoted to one.
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.. method:: Loop.stop()
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Stop the event loop.
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.. method:: Loop.close()
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Close the event loop.
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.. method:: Loop.set_exception_handler(handler)
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Set the exception handler to call when a Task raises an exception that is not
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caught. The *handler* should accept two arguments: ``(loop, context)``.
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.. method:: Loop.get_exception_handler()
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Get the current exception handler. Returns the handler, or ``None`` if no
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custom handler is set.
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.. method:: Loop.default_exception_handler(context)
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The default exception handler that is called.
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.. method:: Loop.call_exception_handler(context)
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Call the current exception handler. The argument *context* is passed through and
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is a dictionary containing keys: ``'message'``, ``'exception'``, ``'future'``.
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