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bpo-39481: Implementation for PEP 585 (#18239)

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This implements things like `list[int]`,
which returns an object of type `types.GenericAlias`.
This object mostly acts as a proxy for `list`,
but has attributes `__origin__` and `__args__`
that allow recovering the parts (with values `list` and `(int,)`.

There is also an approximate notion of type variables;
e.g. `list[T]` has a `__parameters__` attribute equal to `(T,)`.
Type variables are objects of type `typing.TypeVar`.
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Guido van Rossum 2020-04-07 09:50:06 -07:00 • committed by GitHub
parent 9cc3ebd7e0
commit 48b069a003
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30 changed files with 830 additions and 53 deletions
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6
Lib/contextlib.py
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@ -4,7 +4,7 @@ import sys
import _collections_abc
from collections import deque
from functools import wraps
from types import MethodType
from types import MethodType, GenericAlias
__all__ = ["asynccontextmanager", "contextmanager", "closing", "nullcontext",
"AbstractContextManager", "AbstractAsyncContextManager",
@ -16,6 +16,8 @@ class AbstractContextManager(abc.ABC):
"""An abstract base class for context managers."""
__class_getitem__ = classmethod(GenericAlias)
def __enter__(self):
"""Return `self` upon entering the runtime context."""
return self
@ -36,6 +38,8 @@ class AbstractAsyncContextManager(abc.ABC):
"""An abstract base class for asynchronous context managers."""
__class_getitem__ = classmethod(GenericAlias)
async def __aenter__(self):
"""Return `self` upon entering the runtime context."""
return self