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. :-)
