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 | ncoghlan@gmail.com | Brisbane, Australia --------------------------------------------------------------- http://boredomandlaziness.blogspot.com