On Mar 4, 8:04 pm, Robert Kern <robert.k...@gmail.com> wrote: > No, the try: finally: is not implicit. See the source for > contextlib.GeneratorContextManager. When __exit__() gets an exception from the > with: block, it will push it into the generator using its .throw() method. > This > raises the exception inside the generator at the yield statement.
Wow, I just learned something new. My understanding of context managers was that the __exit__ method was guaranteed to be executed regardless of how the context was left. I have often written my own context manager classes, giving them the __enter__ and __exit__ methods. I had mistakenly assumed that the @contextmanager decorator turned a generator function into a context manager with the same behavior as the equivalent context manager class. Now I learn that, no, in order to have the 'undo' code executed in the presence of an exception, you must write your own try/finally block in the generator function. This raises the question in my mind: What's the use case for using @contextmanager rather than wrapping your code in a context manager class that defines __enter__ and __exit__, if you still have to manager your own try/finally block? -- http://mail.python.org/mailman/listinfo/python-list
