Steven D'Aprano a écrit : (snip) > Instead of doing: > > > if callable(function): function() > > you should do: > > try: > function() > except TypeError: > pass
There are time where you may want to know if you have a callable without calling it... > That should work for most uses of callable(), but isn't quite the same. > (What if function() has side-effects, or is expensive, and you want to > determine if it is callable, but not actually call it _now_?) Indeed. The 'correct' replacement would be: if hasattr(obj, '__call__'): # it's a callable but I don't find it so Pythonic to have to check for a __magic__ method. >>Also, what is the replacement of reduce? I think I remember seeing >>somewhere that lists comprehension would be (but also remember the >>advise that reduce will be quicker). > > > No, a list comprehension isn't equivalent to reduce(). There is no > replacement for reduce(). > > Guido has essentially done the functional equivalent of deciding that > because he personally doesn't like for loops, they can and should be > written out as: > > counter = 0 > while counter < len(sequence): > item = sequence[counter] > do_something_with_item > counter += 1 > > because it is "easier to read" than a for loop. > > And yes, if you think my example is extreme because nobody would be that > stupid, that's the point: removing reduce() _is_ that stupid (and it is > not often I say that about a language design decision by Guido!). Python > can, and probably will, get away with it only because reducing an iterable > to a single value is an uncommon operation, and the most common uses of it > (summing a sequence, finding the minimum and maximum) already have > workable replacements. > > It's especially stupid because map() and filter(), both of which do have > simple, easy to understand, completely functional replacements, are going > to stay. reduce() doesn't, and it is going. That's nuts. InMyArms(TM) ! (Guido, if you read us...) -- http://mail.python.org/mailman/listinfo/python-list
