Python abstraction

Question

What is the best way to create a parent class that is able to define a set of methods that will be implemented by the base classes?

The problem comes when a class A requires 2 parameters for method_X, while class B requires 3 parameters for the same method.

How can I solve this issue?

class SuperClass:
 def method_X(self):
 ...
class A(SuperClass):
 def method_X(self, a, b):
 ...
class B(SuperClass):
 def method_X(self, a, b, c):
 ...

• lmiguelvargasf: you can use default arguments to tackle this.
• Martijn Pieters: In short: don't. Your subclasses are breaking the contract set by the superclass.
• wim: This is one of the gripes in the infamous article super harmful.
• Martijn Pieters: @lmiguelvargasf: it still makes it impossible to use subclasses where the contract expected the superclass. You don't know what the method needs.
• chepner: I no longer read the super-harmful article as a criticism of super, but as a complement to Hettinger's super-super that emphasizes that you need to keep the signature of a super-using method consistent across classes.

Answer 1

What you're trying to accomplish is a clear violation of Liskov Substitution Principle. Moreover, defining inconsistent interfaces for the same named methods is going to be messy and would severely limit duck typing. Still, if you want to go with it, I think using kwargs instead of named parameters would serve the purpose.

class SuperClass:
 def method_x(self, **kwargs):
 ...
class A(SuperClass):
 def method_x(self, **kwargs):
 if 'a' in kwargs:
 # Do something