[Python] Handling instances of a context manager inside another context manager

How should a context manager created inside another context manager be handled in Python?

Example: suppose you have class A that acts as a context manager, and class B that also acts as a context manager. But class B instances will have to instantiate and use an instance of class A. I've gone through PEP 343 and this is the solution I thought of:

class A(object):
def __enter__(self):
# Acquire some resources here
return self

def __exit__(seplf, exception_type, exception, traceback):
# Release the resources and clean up
pass


class B(object):
def __init__(self):
self.a = A()

def __enter__(self):
# Acquire some resources, but also need to "start" our instance of A
self.a.__enter__()
return self

def __exit__(self, exception_type, exception, traceback):
# Release the resources, and make our instance of A clean up as well
self.a.__exit__(exception_type, exception, traceback)


Is this the correct approach? Or am I missing some gotchas?

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