I know virtual methods from PHP or Java.
How can they be implemented in Python?
Or have I to define an empty method in an abstract class and override it?
Sure, and you don't even have to define a method in the base class. In Python methods are better than virtual - they're completely dynamic, as the typing in Python is duck typing.
class Dog: def say(self): print "hau" class Cat: def say(self): print "meow" pet = Dog() pet.say() # prints "hau" another_pet = Cat() another_pet.say() # prints "meow" my_pets = [pet, another_pet] for a_pet in my_pets: a_pet.say()
Dog in Python don't even have to derive from a common base class to allow this behavior - you gain it for free. That said, some programmers prefer to define their class hierarchies in a more rigid way to document it better and impose some strictness of typing. This is also possible - see for example the
abc standard module.