Expert Python Programming - Third Edition

The private controversy

For private methods and functions, we usually use a single leading underscore. This is only a naming convention and has no syntactical meaning. But it doesn't mean that leading underscores have no syntactical meaning at all. When a method has two leading underscores, it is renamed on the fly by the interpreter to prevent a name collision with a method from any subclass. This feature of Python is called name mangling.

So some people tend to use a double leading underscore for their private attributes to avoid name collision in the subclasses, for example:

class Base(object):    def __secret(self):        print("don't tell")    def public(self):        self.__secret()class Derived(Base):    def __secret(self):        print("never ever")

From this ...