What must a context manager do if __enter__() fails after acquiring its first subresource?

What must a context manager do if __enter__() fails after acquiring its first subresource?

1. Undo the partial acquisition before propagating, because Python will not call its __exit__().
2. Return True so Python calls __exit__() without exception details.
3. Rely on garbage collection to run __exit__() immediately.
4. Store the resource in the as target so the caller can close it.