Inheriting class attribute with double underscore

Question

I think I understand the concept of \"name mangling\" in python, but there\'s something that I probably missed. Take a look at the following code:

#!/usr/bin/env         


        

Answer 1

As you have noticed, the name used for name mangling is the name of the class where a method is declared, not the derived type of the current object.

The documentation for this feature explicitly gives an example about protecting a variable from a derived class (rather than from external code using an instance variable).

Name mangling is helpful for letting subclasses override methods without breaking intraclass method calls. For 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)