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How Does Python's `super()` Function Handle Multiple Inheritance and Method Resolution Order (MRO)?

Barbara Streisand
Barbara StreisandOriginal
2024-12-29 19:28:12221browse

How Does Python's `super()` Function Handle Multiple Inheritance and Method Resolution Order (MRO)?

Python's super() with Multiple Inheritance

In Python, multiple inheritance involves a class inheriting from multiple parent classes. When using the super() function in such scenarios, it becomes crucial to understand its behavior.

super() in Multiple Inheritance

super() primarily serves two purposes:

  1. To access the immediate parent class's attributes and methods.
  2. To resolve method conflicts when the child class has multiple parent classes.

In the given code snippet:

class First(object):
    def __init__(self):
        print("first")

class Second(object):
    def __init__(self):
        print("second")

class Third(First, Second):
    def __init__(self):
        super(Third, self).__init__()
        print("that's it")

When a Third object is instantiated, the following happens:

  • super(Third, self).__init__() calls First.__init__(self) because First is the first class in the Third class's MRO (Method Resolution Order).
  • First.__init__(self) prints "first."
  • Third.__init__(self) then prints "that's it."

Ambiguous MROs

However, when the inheritance chain becomes more complex, there can be ambiguity in determining the MRO. This occurs when a child class inherits from multiple classes that inherit from the same base class. Python raises an error in such cases.

For example, consider the following code:

class First(object):
    def __init__(self):
        print("first")
        
class Second(First):
    def __init__(self):
        print("second")

class Third(First):
    def __init__(self):
        print("third")

When attempting to create a class that inherits from both Second and Third, Python raises a TypeError due to an ambiguous MRO. The order of the parent classes in the inheritance list is significant and should be consistent across the codebase.

Conclusion

Python's super() function is a powerful tool for managing multiple inheritance. By understanding its behavior, you can effectively resolve method conflicts and maintain a clear class hierarchy.

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