not-context-manager / E1129#

Message emitted:

Context manager '%s' doesn't implement __enter__ and __exit__.

Description:

Used when an instance in a with statement doesn't implement the context manager protocol(__enter__/__exit__).

Correct code:

class MyContextManager:
    def __enter__(self):
        pass

    def __exit__(self, *exc):
        pass


with MyContextManager() as c:
    pass

Problematic code:

class MyContextManager:
    def __enter__(self):
        pass


with MyContextManager() as c:  # [not-context-manager]
    pass

Created by the typecheck checker.