Is it possible (and wise) to extend the None-type ?

[Bruno Desthuilliers]

Stef Mientki a écrit :
> <snip>
>> Alternative (if you *really* want to save the explicit test) is to
>> attach the behaviour modification to the *relevant* class:
>>
>> class NonEvent(Event):
>>    def do_nothing(self):
>>       pass
>>    skip = jump = hop = waltz = saunter = do_nothing
>>    def __len__(self):
>>       return 0
>> NON_EVENT = NonEvent()
>> del NonEvent
>>
>> # later:
>>
>> def amethod(self, event=NON_EVENT):
>>    if event: # still works thanks to __len__ above
>>       event.skip()
>>    # now can avoid test, if desired
>>    event.skip()
>>
>>   
> thanks guys, the Null, Dummy, Skipper, Nonevent class works great

The NullObject pattern is indeed a proven solution. Another one is to 
use a decorator:

def skip_event(event_handler):
    def wrapper(self, event=None):
       if event is not None:
           event.skip()
       return event_handler(self, event)
    wrapper.__name__ = "skip_event_%s" % event_handler.__name__
    wrapper.__doc__  = event_handler.__doc__
    return wrapper

@skip_event
def on_menu_file_open(self, event=None):
    do_something_usefull_here