Timeout context manager for asyncio programs


Keywords
asyncio
License
Apache-2.0
Install
pip install async-timeout==1.2.1

Documentation

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.