How to make python decorator work with inherited classes

Question

I have a piece of code like this and it doesn't work

I'm trying to give instances of some class a unique id here.

def countit(Cls):
  class CC(Cls):
    count = 0
    def __init__(self,*args):
      super(CC, self).__init__(*args)
      self.id = CC.count 
      CC.count += 1
  return CC

class BaseCls(object):
    def __init__(self,x,y):
        self.x=x
        self.y=y

@countit
class Cls(BaseCls):
    def __init__(self,x,y,z):
        super(Cls, self).__init__(x,y)
        self.z=z 

c = Cls(1,2,3) 

I got errors like this

Traceback (most recent call last):
  File "test.py", line 55, in <module>
    c = Cls(1,2,3) 
  File "test.py", line 35, in __init__
    super(CC, self).__init__(*args)
  File "test.py", line 48, in __init__
    super(Cls, self).__init__(x,y)
TypeError: __init__() missing 1 required positional argument: 'z'

Answer 1

The error is because the decorator calls the constructor of the decorated class's base with *args. In this case, z is unexpected.

Suggested approach for this is to use mixins instead of decorators if you want to add functionality to base and derived classes.

Answer 2

Remove the arguments you are passing into super, they are unnecessary. It should fix your issue.