Michael Chermside wrote:
> If I write
>
> with foo:
> BLOCK
>
> where I should have written
>
> with locked(foo):
> BLOCK
>
> ...it silently "succeeds" by doing nothing. I CLEARLY intended to
> do the appropriate cleanup (or locking, or whatever), but it doesn't
> happen.
Ah, thanks. Like Guido, I had something in the back of my head saying it didn't
like the idea, but I couldn't figure out the reason. I think you just nailed it.
Plus, there is a nice alternative which is to provide a 'clean it up if it
needs
it' resource in the standard library:
class resource(object):
def __init__(self, obj):
self.obj = obj
self.enter = getattr(obj, "__enter__", None)
self.exit = getattr(obj, "__exit__", None)
def __enter__(self):
if self.enter is not None:
self.enter()
# For consistency, always return the object
return self.obj
def __exit__(self, *exc_info):
if self.exit is not None:
self.exit(*exc_info)
Then 'I don't know if this needs cleaning up or not' can be written:
with resource(foo):
# If foo needs cleaning up, it will be.
A refinement would provide the option to specify the enter/exit methods
directly:
class resource(object):
def __init__(self, obj, *other_args):
self.obj = obj
if other_args:
if len(other_args) != 2:
raise TypeError("need 1 or 3 arguments")
self.enter = args[0]
self.exit = None
self.exit_no_args = args[1]
else:
self.enter = getattr(obj, "__enter__", None)
self.exit = getattr(obj, "__exit__", None)
self.exit_no_args = None
def __enter__(self):
if self.enter is not None:
self.enter()
# For consistency, always return the object
return self.obj
def __exit__(self, *exc_info):
if self.exit is not None:
self.exit(*exc_info)
elif self.exit_no_args is not None:
self.exit()
That would let any object with a standard 'clean me up method' be easily used
in
a with statement:
with resource(bar, None, bar.clear):
# bar will be cleared when we're done
Cheers,
Nick.
--
Nick Coghlan | [EMAIL PROTECTED] | Brisbane, Australia
---------------------------------------------------------------
http://boredomandlaziness.blogspot.com
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