python3 use of abstract base class for inheriting attributes

Question

I am trying to use an abstract base class using the abc.ABCMeta . Here is the sample code -

import abc
class A(metaclass=abc.ABCMeta):
 def __init__(self):
 self.v1 = 10
 self.v2 = 10
 @abc.abstractmethod
 def first_method(self):
 pass
class B(A):
 def __init__(self):
 self.v2= 20
 def first_method(self):
 pass
if __name__ == '__main__':
 b = B()
 print("v1 =%d", b.v1)
 print("v2=%d", b.v2)

If I do not define __init__ in class B, it would just take the values of v1 and v2 from the superclass A. But,I want to use the value of v1 from the abstract class A and override the value of variable v2. If I try to call super.__init__(self) it gives an error. Can someone please let me know the way to accomplish this? Thank you.

UPDATE: Got the following error message with the above sample code: AttributeError: 'B' object has no attribute 'v1'

• Caramiriel: What does the error say :) ?
• cppb: sorry, it says AttributeError: 'B' object has no attribute 'v1'
• Caramiriel: I meant with super().__init__(self) included? It probably says __init__() takes 1 positional argument but 2 were given. Try without the self parameter, its already included in the super() call.
• cppb: ha! you got it... super().__init__() please post the answer so that i can accept :-)
• Caramiriel: You can pick Yaroslav's answer, no need to double post it :)

Answer 1

You should use super().__init__() instead of super.__init__(self).

Answer 2

this should work.

import abc
class A(metaclass=abc.ABCMeta):
 def __init__(self):
 self.v1 = 10
 self.v2 = 10
 @abc.abstractmethod
 def first_method(self):
 pass
class B(A):
 def __init__(self):
 super(B, self).__init__()
 self.v2 = 20
 def first_method(self):
 pass
if __name__ == '__main__':
 b = B()
 print('v1 = ', b.v1)
 print('v2 = ', b.v2)

• chepner: This is essentially the same answer as Yaroslav, except it doesn't work with Python 3. (It would be correct for Python 2, but that's not what the OP is using.)
• chepner: No, it doesn't. Compare type(A) in Python 2 and 3; Python 3 doesn't look at the __metaclass__ attribute in the definition, so A isn't an abstract base class.
• Ziyad Mestour: @chepner, you're right...now it is Python3 compatible
• chepner: It is, but you aren't adding anything relevant that Yaroslav's answer doesn't already cover.
• Ziyad Mestour: I did not notice it, until I posted.