asyncstdlib library re-implements functions and classes of the Python
standard library to make them compatible with
async callables, iterables
and context managers.
It is fully agnostic to
async event loops and seamlessly works with
asyncio, third-party libraries such as
trio, as well as
async event loop.
Standard Library Modules¶
All re-implementations are located in submodules of
with the same name as those of the Python standard library.
The Async Library Module¶
The core toolset used by
asyncstdlib itself is available
as a separate submodule.
Async Neutral Arguments¶
Many objects of
asyncstdlib are async neutral – they accept
both regular and async arguments.
Type annotations use (async) to denote async neutral objects.
For example, the annotation (int, …) → (async) bool denotes a call that takes an
int and either returns a boolean directly or requires
return a boolean.
Whether a call is regular or async is determined by inspecting its
return type at runtime.
This supports async-producing factories, such as an
function wrapped in
However, this also means that the result must consistently be either
regular or async.
Async Iterator Cleanup¶
Cleanup of async iterables is special in that
aclose() may require
an active event loop. This is not given when garbage collection finalizes an
async iterable via its
__del__() method. Thus, async iterators
should be cleaned up deterministically whenever possible (see PEP 533 for details).
All async iterators of
asyncstdlib that work on other iterators
assume sole ownership of the iterators passed to them.
Passed in async iterators are guaranteed to
aclose() as soon as
asyncstdlib async iterator itself is cleaned up.
borrow() to prevent automatic cleanup,
scoped_iter() to guarantee cleanup in custom code.