How to invoke the super constructor in Python

Question

class A      def   init   self           print  world    class B A       def   init   self          print  hello    B      output  hello   In all other languages I ve worked with the super constructor is invoked implicitly  How does one invoke it in Python  I would expect super self  but this doesn t work

User · Answer

With Python 2 x old-style classes it would be this   class A    def   init   self       print  world    class B A     def   init   self       print  hello      A   init   self

User · Answer

I use the following formula that extends previous answers   class A object    def   init   self      print  world   class B A    def   init   self      print  hello     super self   class    self    init      B     This way you don t have to repeat the name of the class in the call to super  It can come handy if you are coding a large number of classes  and want to make your code in the initialiser methods independent of the class name

User · Answer

Short Answer  super DerivedClass  self    init       Long Answer  What does super   do   It takes specified class name  finds its base classes  Python allows multiple inheritance  and looks for the method    init   in this case  in each of them from left to right  As soon as it finds method available  it will call it and end the search   How do I call init of all base classes   Above works if you have only one base class  But Python does allow multiple inheritance and you might want to make sure all base classes are initialized properly  To do that  you should have each base class call init   class Base1    def   init          super Base1  self    init      class Base2    def   init          super Base2  self    init      class Derived Base1  Base2     def   init          super Derived  self    init       What if I forget to call init for super   The constructor    new    gets invoked in a chain  like in C   and Java   Once the instance is created  only that instance s initialiser    init    is called  without any implicit chain to its superclass

User · Answer

super   returns a parent-like object in new-style classes   class A object       def   init   self           print  world    class B A       def   init   self           print  hello           super B  self    init      B

User · Answer

Just to add an example with parameters   class B A       def   init   self  x  y  z           A   init   self  x  y    Given a derived class B that requires the variables x  y  z to be defined  and a superclass A that requires x  y to be defined  you can call the static method init of the superclass A with a reference to the current subclass instance  self  and then the list of expected arguments

User · Answer

In line with the other answers  there are multiple ways to call super class methods  including the constructor   however in Python-3 x the process has been simplified   Python-2 x  class A object    def   init   self      print  world   class B A    def   init   self      print  hello     super B  self    init       Python-3 x  class A object    def   init   self      print  world    class B A    def   init   self      print  hello      super     init       super   is now equivalent to super  lt containing classname gt   self  as per the docs

User · Answer

One way is to call A s constructor and pass self as an argument  like so   class B A       def   init   self           A   init   self          print  hello    The advantage of this style is that it s very clear   It call A s initialiser   The downside is that it doesn t handle diamond-shaped inheritance very well  since you may end up calling the shared base class s initialiser twice   Another way is to use super    as others have shown   For single-inheritance  it does basically the same thing as letting you call the parent s initialiser   However  super   is quite a bit more complicated under-the-hood and can sometimes be counter-intuitive in multiple inheritance situations   On the plus side  super   can be used to handle diamond-shaped inheritance   If you want to know the nitty-gritty of what super   does  the best explanation I ve found for how super   works is here  though I m not necessarily endorsing that article s opinions

[python] How to invoke the super constructor in Python?

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