Diamon Problem, 2 superclasses implementing methods with the same name. To support multiple inheritance, programming languages should solve the Diamond Problem, this the potential conflict of 2 superclasses implementing a method with the same name. Instead of subclassing the built-ins, derive your classes from the collections module using UserDict, UserList, and UserString, which are designed to be easily extended. In the original author's words of the book Fluent Python about the subject: Subclassing built-in types like dict or list or str directly is error prone because the built-in methods mostly ignore user-defined overrides. the _getitem_ of AnswerDict should execute instead we have the original _getitem_ of the superclass dict executing.
What's happening is breaking OOP rules, as looking for the method to execute should start from the subclass even if the call comes from a superclass's method, i.e. The issue here is that the _getitem_ of AnswerDict is bypassed by the dict.update method. Let's try something: class AnswerDict(dict): Subclassing a built-in type isn't always simple, this is the case of Python's CPython implementation which is the prevalent implementation of Python to date. Why You Should Never Subclass a Built-In Type? You see here we called the super()._setitem_(key, value), this the superclass (OrderedDict) invocation of its _setitem_ method. """Store items in the order they were last updated""" This specific method is used when a subclass overrides a method of a superclass, the overriding method usually needs to call the corresponding method of the superclass.įor example, creating a class to store items in the order they were last updated: class LastUpdatedOrderedDict(OrderedDict):
Just like Java and C#, Python supports the use of a built-in function, super(), to call its superior class and it is essential to use it consistently to well-maintain our program. Today we will discuss the importance of inheritance, multiple inheritance and how and when we should use it, but first we will start with the basic super() function invocation. Only Python supports multiple inheritance too, which is the ability of a class to have more than one base class or superior class. Inheritance is a corner stone of any object oriented programming language, and in Python, it is as important.
#SUPER IN OOP PYTHON FULL#
The Full Guide to Multiple Inheritance and Mixins in Python Inheritance in Python
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