Inheritance and Overriding init in python

Question

I was reading  Dive Into Python  and in the chapter on classes it gives this example   class FileInfo UserDict        store file metadata      def   init   self  filename None           UserDict   init   self          self  name     filename   The author then says that if you want to override the   init   method  you must explicitly call the parent   init   with the correct parameters      What if that FileInfo class had more than one ancestor class      Do I have to explicitly call all of the ancestor classes    init   methods     Also  do I have to do this to any other method I want to override

User · Answer

You don t really have to call the   init   methods of the base class es   but you usually want to do it because the base classes will do some important initializations there that are needed for rest of the classes methods to work   For other methods it depends on your intentions  If you just want to add something to the base classes behavior you will want to call the base classes method additionally to your own code  If you want to fundamentally change the behavior  you might not call the base class  method and implement all the functionality directly in the derived class

User · Answer

The book is a bit dated with respect to subclass-superclass calling   It s also a little dated with respect to subclassing built-in classes   It looks like this nowadays   class FileInfo dict          store file metadata        def   init   self  filename None           super FileInfo  self    init             self  name     filename   Note the following    We can directly subclass built-in classes  like dict  list  tuple  etc  The super function handles tracking down this class s superclasses and calling functions in them appropriately

User · Answer

In each class that you need to inherit from  you can run a loop of each class that needs init d upon initiation of the child class   an example that can copied might be better understood     class Female Grandparent      def   init   self           self grandma name    Grandma   class Male Grandparent      def   init   self           self grandpa name    Grandpa   class Parent Female Grandparent  Male Grandparent       def   init   self           Female Grandparent   init   self          Male Grandparent   init   self           self parent name    Parent Class   class Child Parent       def   init   self           Parent   init   self   ---------------------------------------------------------------------------------------          for cls in Parent   bases      This block grabs the classes of the child              cls   init   self         class  which is named  Parent  in this case                                           and iterates through them  initiating each one                                         The result is that each parent  of each child                                         is automatically handled upon initiation of the                                         dependent class  WOOT WOOT   D  ---------------------------------------------------------------------------------------     g   Female Grandparent   print g grandma name  p   Parent   print p grandma name  child   Child    print child grandma name

User · Answer

Yes  you must call   init   for each parent class  The same goes for functions  if you are overriding a function that exists in both parents

User · Answer

If the FileInfo class has more than one ancestor class then you should definitely call all of their   init     functions  You should also do the same for the   del     function  which is a destructor

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