139. Using super() for Method Resolution

In Python, the super() function is used to call methods from a superclass in the context of method resolution order (MRO), especially in multiple inheritance scenarios. It helps to access methods in the inheritance chain without explicitly referring to the superclass by name.

Here are 10 Python code snippets demonstrating how to use super() for method resolution in various inheritance scenarios:

1. Basic Single Inheritance with super()

In simple inheritance, super() can be used to call a method from the parent class.

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class Animal:
    def speak(self):
        print("Animal speaks")

class Dog(Animal):
    def speak(self):
        super().speak()  # Calling parent class method
        print("Dog barks")

dog = Dog()
dog.speak()

Output:

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Animal speaks
Dog barks

2. Multiple Inheritance with super()

In multiple inheritance, super() follows the method resolution order (MRO) to call methods from all superclasses.

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class A:
    def method(self):
        print("Method from class A")

class B:
    def method(self):
        print("Method from class B")

class C(A, B):
    def method(self):
        super().method()  # Calls method from class A (MRO order)
        print("Method from class C")

c = C()
c.method()

Output:

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Method from class A
Method from class C

3. Using super() with __init__() in Multiple Inheritance

When initializing classes with __init__() in multiple inheritance, super() ensures the initialization of all parent classes.

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class A:
    def __init__(self):
        print("A initialized")

class B:
    def __init__(self):
        print("B initialized")

class C(A, B):
    def __init__(self):
        super().__init__()

c = C()

Output:

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A initialized

In this example, since class A appears first in the MRO, its __init__() method is called.

4. super() in Diamond Problem (Multiple Inheritance)

When multiple classes share a common base class, super() resolves the diamond problem (a situation where a class inherits from two classes that have the same parent).

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class A:
    def method(self):
        print("Method from class A")

class B(A):
    def method(self):
        super().method()
        print("Method from class B")

class C(A):
    def method(self):
        super().method()
        print("Method from class C")

class D(B, C):
    def method(self):
        super().method()
        print("Method from class D")

d = D()
d.method()

Output:

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Method from class A
Method from class C
Method from class B
Method from class D

In this case, the MRO ensures that super() calls methods in the correct order.

5. Calling a Parent Method from a Subclass in Multiple Inheritance

Use super() to call a method from a parent class in cases where multiple parent classes share the same method name.

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class A:
    def hello(self):
        print("Hello from A")

class B:
    def hello(self):
        print("Hello from B")

class C(A, B):
    def hello(self):
        super().hello()  # Calls hello() from class A (based on MRO)
        print("Hello from C")

c = C()
c.hello()

Output:

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Hello from A
Hello from C

6. Avoiding Explicit Class Names with super()

You don't need to refer to the parent class explicitly when calling super(), making it more flexible in future changes.

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class A:
    def show(self):
        print("Class A")

class B(A):
    def show(self):
        super().show()  # Avoids explicitly using class name
        print("Class B")

b = B()
b.show()

Output:

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Class A
Class B

7. Super with __del__() Method

You can use super() in the __del__() method to ensure proper cleanup when an object is deleted.

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class A:
    def __del__(self):
        print("Class A cleanup")

class B(A):
    def __del__(self):
        super().__del__()
        print("Class B cleanup")

b = B()
del b

Output:

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Class A cleanup
Class B cleanup

8. Super in Method Overriding with Arguments

Use super() to call overridden methods and pass arguments.

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class A:
    def speak(self, message):
        print(f"A says: {message}")

class B(A):
    def speak(self, message):
        super().speak(message)  # Passes argument to the parent method
        print(f"B says: {message}")

b = B()
b.speak("Hello!")

Output:

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A says: Hello!
B says: Hello!

9. Calling super() with staticmethod

You can use super() in a static method to call a static method from a parent class.

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class A:
    @staticmethod
    def greet():
        print("Hello from A")

class B(A):
    @staticmethod
    def greet():
        super().greet()  # Calls static method from A
        print("Hello from B")

b = B()
b.greet()

Output:

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Hello from A
Hello from B

10. Using super() in a Method with Arguments in Multiple Inheritance

In complex inheritance, super() helps in invoking methods from parent classes that accept arguments.

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class A:
    def greet(self, name):
        print(f"Hello, {name} from A")

class B:
    def greet(self, name):
        print(f"Hello, {name} from B")

class C(A, B):
    def greet(self, name):
        super().greet(name)  # Calls greet() from A
        print(f"Hello, {name} from C")

c = C()
c.greet("Alice")

Output:

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Hello, Alice from A
Hello, Alice from C

Explanation:

• The super() function follows the method resolution order (MRO) and calls methods from superclasses in the defined order.

• In a multiple inheritance scenario, super() allows you to avoid explicitly calling a class name, making the code more maintainable and flexible.

Summary:

• super() is used to call methods from parent classes, especially when dealing with multiple inheritance.

• It helps in avoiding redundant method calls and simplifies the inheritance structure.

• The method resolution order (MRO) ensures the correct order of method calls in complex class hierarchies.