async-timeout

asyncio-compatible timeout context manager.

DEPRECATED

This library has effectively been upstreamed into Python 3.11+.

Therefore this library is considered deprecated and no longer actively supported.

Version 5.0+ provides dual-mode when executed on Python 3.11+: asyncio_timeout.Timeout is fully compatible with asyncio.Timeout and old versions of the library.

Anyway, using upstream is highly recommended. asyncio_timeout exists only for the sake of backward compatibility, easy supporting both old and new Python by the same code, and easy misgration.

If rescheduling API is not important and only async with timeout(...): ... functionality is required, a user could apply conditional import:

if sys.version_info >= (3, 11):
    from asyncio import timeout, timeout_at
else:
    from async_timeout import timeout, timeout_at

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) call returns a context manager that cancels a block on timeout expiring:

from async_timeout import timeout
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() / .expired for check if timeout happens exactly in context manager:

async with timeout(1.5) as cm:
    await inner()
print(cm.expired())  # recommended api
print(cm.expired)    # compatible api

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 .when() / .deadline:

async with timeout(1.5) as cm:
    cm.when()    # recommended api
    cm.deadline  # compatible api

Not finished yet timeout can be rescheduled by shift() or update() methods:

async with timeout(1.5) as cm:
    # recommended api
    cm.reschedule(cm.when() + 1)  # add another second on waiting
    # compatible api
    cm.shift(1)  # add another second on waiting
    cm.update(loop.time() + 5)  # reschedule to now+5 seconds

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

Disable scheduled timeout:

async with timeout(1.5) as cm:
    cm.reschedule(None)  # recommended api
    cm.reject()          # compatible api

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.