And if I leave A as is, but redefine B and C as so:

    >>> class B(A):
    ...   def my_method(self):
    ...     super(B, self).my_method()
    ...     print 'and BBBBB'
    ... 
    >>> class C(B):
    ...   def my_method(self):
    ...     super(C, self).my_method()
    ...     print 'and CCCCC'
    ... 
    >>> c = C()
    >>> c.my_method()
    AAAAA
    and BBBBB
    and CCCCC
    >>>