superclassmethod.py

>>> class A(object):
...     def __init__(self, a):
...         self.a = a
...     @classmethod
...     def f(cls, a):
...         return cls(a)
...
>>> class B(A):
...     def __init__(self, a, b):
...         super(B, self).__init__(a)
...         self.b = b
...
>>> A.f(2)
<__main__.A object at 0x100cf5450>
>>> B.f(3)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 6, in f
TypeError: __init__() takes exactly 3 arguments (2 given)