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asyncio/coroutines.py

cpython 3.14 @ ab2d84fe1023/Lib/asyncio/coroutines.py

Overview​

coroutines.py provides two public predicates used throughout the asyncio machinery: iscoroutine and iscoroutinefunction. It also housed the @coroutine decorator that bridged generator-based coroutines into the async def world, but that decorator was deprecated in Python 3.11 and removed in 3.12. The file today is roughly 80 lines of focused utility code.

Reading​

iscoroutine​

iscoroutine(obj) returns True when obj is a coroutine object. The check is a thin wrapper around inspect.iscoroutine, which ultimately tests whether the underlying code object carries the CO_COROUTINE flag:

# CPython: Lib/asyncio/coroutines.py
def iscoroutine(obj):
    """Return True if obj is a coroutine object."""
    return inspect.iscoroutine(obj)

In the C layer, CO_COROUTINE is bit 0x0100 of co_flags. Any async def body compiles to a code object with that flag set, so a live coroutine (the object returned when you call an async def function without await) passes this test.

iscoroutinefunction​

iscoroutinefunction(obj) handles the decorated-function case that a plain inspect.iscoroutinefunction call would miss. Decoration layers such as functools.wraps store the original callable in __wrapped__, so asyncio walks the chain:

# CPython: Lib/asyncio/coroutines.py
def iscoroutinefunction(obj):
    """Return True if obj is a coroutine function."""
    return (inspect.iscoroutinefunction(obj) or
            getattr(obj, '_is_coroutine', None) is _is_coroutine)

The sentinel _is_coroutine = object() is an identity token rather than a plain boolean, which prevents external code from spoofing the attribute with True. Third-party decorators that want asyncio compatibility set wrapper._is_coroutine = asyncio.coroutines._is_coroutine on their wrapper.

gopy mirror​

This file is not yet ported. When ported it will live at module/asyncio/coroutines.go and export Iscoroutine and Iscoroutinefunction as Go functions operating on objects.Object.

CPython 3.14 changes​

  • The @coroutine generator-wrapper decorator was removed in 3.12; no trace of it remains in 3.14.
  • iscoroutinefunction behaviour is unchanged but the internal sentinel pattern is stable and considered public API.
  • No further removals are planned for 3.14 in this file.