paoli...@gmail.com writes: > The official Python tutorial at > > https://docs.python.org/3/tutorial/classes.html#private-variables > > says that "name mangling is helpful for letting subclasses override methods > without breaking intraclass method calls" and makes an interesting example: > > class Mapping: > def __init__(self, iterable): > self.items_list = [] > self.__update(iterable) > > def update(self, iterable): > for item in iterable: > self.items_list.append(item) > > __update = update # private copy of original update() method > > class MappingSubclass(Mapping): > > def update(self, keys, values): > # provides new signature for update() > # but does not break __init__() > for item in zip(keys, values): > self.items_list.append(item) > > > It seems to me that, in this example, one could just have: > > class Mapping: > def __init__(self, iterable): > self.items_list = [] > Mapping.update(self, iterable) > > def update(self, iterable): > for item in iterable: > self.items_list.append(item) > > and avoid copying 'Mapping.update' into 'Mapping.__update'. More generally, > any time one needs to "let subclasses override methods without breaking > intraclass method calls" (the goal stated in the tutorial), using qualified > access to class attributes/methods should suffice. > > Am I missing something? Is 'self.__update(iterable)' in 'Mapping.__init__' > preferable to 'Mapping.update(self, iterable)'? > > I think that, instead, name mangling is helpful to avoid accidental overrides > of methods/attributes by the *current* class (rather than its subclasses). > Given the way that C3 linearization works, you can't know in advance who will > follow your class A in B.__mro__ when B extends A. Name mangling allows you > to avoid overriding methods/attributes of classes that might follow. > > Any thoughts?
You can do that indeed for class level attributes (such as methods); you cannot do it for instance level attributes (e.g. holding instance specific values). >From my point of view, "__" name mangling is particularly interesting for mixin classes (i.e. classes implementing a single feature and being designed to be used in deriving classes combining the necessary features by deriving from all features classes required). Those classes are typically combined with other classes - with a corresponding risk of name clashes. Therefore, the above name mangling is helpful to reduce that risk for private attributes (whether methods or data attributes). -- https://mail.python.org/mailman/listinfo/python-list
