* contextlib.pyi ExitStack.callback take Callable
The documentation for ExitStack does not specify the return type of the callable's passed to callback.
Saying that they always return None breaks a very common use case for ExitStack, which is to "schedule" changes to a collection
while iterating it.
```
with ExitStack() as stack:
for key, value in adict.items():
if ...:
stack.callback(adict.pop, key)
```
I also added AsyncExitStack, using Awaitable.
* Moving to Explicit Any in Generics
* add typing.ContextManager for 3.6+ only
This fixes the easier part of #655.
Would it make sense to add a generic typing.ContextManager that exists in any Python version?
* update comment
* fix argument types for ContextManager.__exit__
* add AsyncContextManager
* add @asynccontextmanager
* typing.ContextManager now always exists
* back out async-related changes
Will submit those in a separate PR later
* fix import order
* AbstractContextManager only exists in 3.6+
* AbstractContextManager -> ContextManager
mypy could not recognize the case when we use contextmanager as a
decorator, which has been supported since Python 3.2.
In the following code snippet,
from contextlib import contextmanager
@contextmanager
def foo(arg1):
try:
print(arg1)
print('1')
yield
finally:
print('2')
@foo('0')
def foo2():
print('3')
foo2()
we get mypy error as follows,
error: ContextManager[Any] not callable
The suggested changes can fix this error and properly reflect the
updated contextmanager usage pattern.
To be on the conservative side I'm making it an Iterable of values;
this should be good enough for common usages.
The types of the values actually correspond to the types of the
argument ContextManagers, but a proper signature would require
variadic type variables (https://github.com/python/typing/issues/193),
which isn't worth waiting for. :-)
