Chain-calling parent initialisers in python
PythonOopInheritanceConstructorPython Problem Overview
Consider this - a base class A, class B inheriting from A, class C inheriting from B. What is a generic way to call a parent class initialiser in an initialiser? If this still sounds too vague, here's some code.
class A(object):
def __init__(self):
print "Initialiser A was called"
class B(A):
def __init__(self):
super(B,self).__init__()
print "Initialiser B was called"
class C(B):
def __init__(self):
super(C,self).__init__()
print "Initialiser C was called"
c = C()
This is how I do it now. But it still seems a bit too non-generic - you still must pass a correct type by hand.
Now, I've tried using self.__class__
as a first argument to super(), but, obviously it doesn't work - if you put it in the initialiser for C - fair enough, B's initialiser gets called. If you do the same in B, "self" still points to an instance of C so you end up calling B's initialiser again (this ends in an infinite recursion).
There is no need to think about diamond inheritance for now, I am just interested in solving this specific problem.
Python Solutions
Solution 1 - Python
Python 3 includes an improved super() which allows use like this:
super().__init__(args)
Solution 2 - Python
The way you are doing it is indeed the recommended one (for Python 2.x).
The issue of whether the class is passed explicitly to super
is a matter of style rather than functionality. Passing the class to super
fits in with Python's philosophy of "explicit is better than implicit".
Solution 3 - Python
You can simply write :
class A(object):
def __init__(self):
print "Initialiser A was called"
class B(A):
def __init__(self):
A.__init__(self)
# A.__init__(self,<parameters>) if you want to call with parameters
print "Initialiser B was called"
class C(B):
def __init__(self):
# A.__init__(self) # if you want to call most super class...
B.__init__(self)
print "Initialiser C was called"