async-timeout
=============
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asyncio-compatible timeout context manager.


Usage example
-------------


The context manager is useful in cases when you want to apply timeout
logic around block of code or in cases when ``asyncio.wait_for()`` is
not suitable. Also it's much faster than ``asyncio.wait_for()``
because ``timeout`` doesn't create a new task.

The ``timeout(delay, *, loop=None)`` call returns a context manager
that cancels a block on *timeout* expiring::

   async with timeout(1.5):
       await inner()

1. If ``inner()`` is executed faster than in ``1.5`` seconds nothing
   happens.
2. Otherwise ``inner()`` is cancelled internally by sending
   ``asyncio.CancelledError`` into but ``asyncio.TimeoutError`` is
   raised outside of context manager scope.

*timeout* parameter could be ``None`` for skipping timeout functionality.


Alternatively, ``timeout_at(when)`` can be used for scheduling
at the absolute time::

   loop = asyncio.get_event_loop()
   now = loop.time()

   async with timeout_at(now + 1.5):
       await inner()


Please note: it is not POSIX time but a time with
undefined starting base, e.g. the time of the system power on.


Context manager has ``.expired`` property for check if timeout happens
exactly in context manager::

   async with timeout(1.5) as cm:
       await inner()
   print(cm.expired)

The property is ``True`` if ``inner()`` execution is cancelled by
timeout context manager.

If ``inner()`` call explicitly raises ``TimeoutError`` ``cm.expired``
is ``False``.

The scheduled deadline time is available as ``.deadline`` property::

   async with timeout(1.5) as cm:
       cm.deadline

Not finished yet timeout can be rescheduled by ``shift_by()``
or ``shift_to()`` methods::

   async with timeout(1.5) as cm:
       cm.shift_by(1)  # add another second on waiting
       cm.shift_to(loop.time() + 5)  # reschedule to now+5 seconds

Rescheduling is forbidden if the timeout is expired or after exit from ``async with``
code block.


Installation
------------

::

   $ pip install async-timeout

The library is Python 3 only!



Authors and License
-------------------

The module is written by Andrew Svetlov.

It's *Apache 2* licensed and freely available.