On 25/06/2010 19:35, Michael Foord wrote:
Hello all,
I've put a recipe up on the Python cookbook for creating APIs that
work as both decorators and context managers and wonder if it would be
considered a useful addition to the functools module.
http://code.activestate.com/recipes/577273-decorator-and-context-manager-from-a-single-api/
Actually contextlib would be a much more sensible home for it.
Michael
I wrote this after writing almost identical code the second time for
"patch" in the mock module. (The patch decorator can be used as a
decorator or as a context manager and I was writing a new variant.)
Both py.test and django have similar code in places, so it is not an
uncommon pattern.
It is only 40 odd lines (ignore the ugly Python 2 & 3 compatibility
hack), so I'm fine with it living on the cookbook - but it is at least
slightly fiddly to write and has the added niceness of providing the
optional exception handling semantics of __exit__ for decorators as well.
Example use (really hope email doesn't swallow the whitespace - my
apologies in advance if it does):
from context import Context
class mycontext(Context):
def __init__(self, *args):
"""Normal initialiser"""
def start(self):
"""
Called on entering the with block or starting the decorated
function.
If used in a with statement whatever this method returns will
be the
context manager.
"""
def finish(self, *exc):
"""
Called on exit. Arguments and return value of this method have
the same meaning as the __exit__ method of a normal context
manager.
"""
@mycontext('some', 'args')
def function():
pass
with mycontext('some', 'args') as something:
pass
I'm not entirely happy with the name of the class or the start and
finish methods, so open to suggestions there. start and finish *could*
be __enter__ and __exit__ - but that would make the class you
implement *look* like a normal context manager and I thought it was
better to distinguish them. Perhaps before and after?
All the best,
Michael Foord
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