On Sat, Sep 11, 2010 at 3:16 PM, Robert Collins
<[email protected]> wrote:
> This shows a behaviour of context managers that is undesirable for test
> suites:
I had a hard to debug failure where a context manager was being used
as a test fixture - it did some monkey patching and then cleaned up:
@contextmanager
def with_monkey_patched_thing():
monkey_patch()
yield
revert_monkey_patch()
The end result was the cleanup never got called if the test raised an
exception. The yield needs to be in a try: finally: block to ensure
cleanup occurs.
@contextmanager
def with_monkey_patched_thing():
try:
monkey_patch()
yield
finally:
revert_monkey_patch()
> from contextlib import contextmanager
>
> @contextmanager
> def raiser(message):
> yield
> print "cleanup", message
> raise RuntimeError(message)
>
> with raiser("outer"):
> with raiser("inner"):
> print "test code"
>
>
> :!python demo.py
> test code
> cleanup inner
> Traceback (most recent call last):
> File "demo.py", line 11, in <module>
> print "test code"
> File "/usr/lib/python2.6/contextlib.py", line 23, in __exit__
> self.gen.next()
> File "demo.py", line 7, in raiser
> raise RuntimeError(message)
> RuntimeError: inner
>
> In a test suite we want to run all the cleanups, *and* we want to
> report on all the exceptions.
--
Stuart Bishop <[email protected]>
http://www.stuartbishop.net/
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