Question

I was reading the Python docs about classes and came across this paragraph which I’m not sure about:

Derived classes may override methods
of their base classes. Because methods
have no special privileges when
calling other methods of the same
object, a method of a base class that
calls another method defined in the
same base class may end up calling a
method of a derived class that
overrides it. (For C++ programmers:
all methods in Python are effectively
virtual.)

Example:

class A:
    def foo(self):
        self.bar()

    def bar(self):
        print "from A"

class B(A):
    def foo(self):
        self.bar()

    def bar(self):
        print "from B"

Does this mean that an object of class A obj = A() can somehow end up printing “from B”? Am I reading this correctly? I apologize if this doesn’t make sense. I’m a bit confused as to how python handles Inheritance and overriding. Thanks!

Answer 1

No. There’s no way the superclass can know anything about the subclass. What it means is if you instantiate the subclass B, and it inherits a method foo(), and overrides a method bar(), then when you call foo(), that will call the bar() definition in B, not the bar() definition in A. This is not what the superclass writer intended – he expected his call to bar() to go to his own definition.