Bryan wrote: > Steven Bethard wrote: > >> The advantage of a functional form over a method shows up when you >> write a function that works on a variety of different types. Below are >> implementations of "list()", "sorted()" and "join()" that work on any >> iterable and only need to be defined once:: >> >> def list(iterable): >> result = [] >> for item in iterable: >> result.append(item) >> return result >> >> def sorted(iterable): >> result = list(iterable) >> result.sort() >> return result >> >> def join(iterable): >> # this is more efficient in C, where the string's buffer can be >> # pre-allocated before iterating through the loop. >> result = '' >> for item in iterable: >> result += item >> return result >> >> Now, by providing these as functions, I only have to write them once, >> and they work on *any* iterable, including some container object that >> you invent tomorrow. >> >> If everything were methods, when you invented your container object >> tomorrow, you'd have to reimplement these methods on your class. (Or >> we'd have to introduce a Container class to provide them, and everyone >> would have to inherit from that if they wanted to define a container.) > > could you get the same result by putting these methods in base class > object that everything subclasses? then you wouldn't have to > reimplement these methods on your class either, right?
Well, you don't want to put them on object, because not everything is a container (e.g. you don't want the sorted() method on ints). So you have to put them on some subclass of object and then require everyone who every creates a container class to inherit from that object. Python generally frowns upon required inheritance from a particular type, but at the same time, it does provide things like UserDict.DictMixin for something very much along these lines. But I don't think too many folks want to *require* that every dict-like object inherit from DictMixin. STeVe -- http://mail.python.org/mailman/listinfo/python-list
