Usage

from virtualmethod import virtualmethod

class Base(object):
    @virtualmethod
    def my_virtual_method(self):
        print "This is a virtual method. Call me from a subclass!"

class A(Base):
    pass

class B(Base):
    def my_virtual_method(self):
        print "I went ahead and implemented my own version."

base = Base()
a = A()
b = B()

a.my_virtual_method()
-> This is a virtual method. Call me from a subclass!

b.my_virtual_method()
-> I went ahead and implemented my own version.

base.my_virtual_method()
-> Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "virtualmethod/core.py", line 11, in __call__
    raise TypeError("Virtual method %s must be called from a subclass." % self.__name__)
TypeError: Virtual method my_virtual_method must be called from a subclass.

Note(s)

@virtualmethod works with @classmethod and @staticmethod, but must be declared first, i.e.:

@virtualmethod
@classmethod
def my_virtual_class_method(cls):
    ...

Credit

Thanks to Patrick Hensley for his input, and to Denis Ryzhkov for his method_decorator module.