11.4 Overloading operators

Magic methods in Python are special methods that customize how objects behave. They let you define how your custom classes work with built-in operations, making your code more intuitive and powerful.

By implementing magic methods, you can make your objects act like built-in types. This allows for natural syntax when working with custom objects, enhancing their functionality and making your code more expressive and easier to use.

Magic Methods and Operator Overloading

Purpose of magic methods

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• Magic methods, also known as dunder methods, are special methods in Python classes that have double underscores before and after their names (

  [__init__](https://www.fiveableKeyTerm:__init__)

  ,

  [__str__](https://www.fiveableKeyTerm:__str__)

  ,

  [__repr__](https://www.fiveableKeyTerm:__repr__)

  ,

  [__add__](https://www.fiveableKeyTerm:__add__)

  ,

  [__eq__](https://www.fiveableKeyTerm:__eq__)

  )
• Customize the behavior of built-in operations and functions for user-defined objects
  • Allow classes to emulate the behavior of built-in types (lists, dictionaries)
  • Enhance the functionality and interactivity of custom classes (custom string representations, arithmetic operations)
• Implementing magic methods involves defining the desired magic method within the class definition using the appropriate name and signature
  • The method's functionality determines how the corresponding operation or function will behave for instances of the class (

    __str__

    defines string representation,

    __add__

    defines addition behavior)
• Magic methods are a key aspect of polymorphism in Python, allowing objects of different classes to respond to the same operations in different ways

Arithmetic operators for custom classes

• Arithmetic operators can be overloaded for custom classes by defining the corresponding magic methods
• Common arithmetic operator magic methods:

  1. __add__(self, other)

     overloads the

     +

     operator

  2. [__sub__](https://www.fiveableKeyTerm:__sub__)(self, other)

     overloads the

     -

     operator

  3. [__mul__](https://www.fiveableKeyTerm:__mul__)(self, other)

     overloads the

     *

     operator

  4. [__truediv__](https://www.fiveableKeyTerm:__truediv__)(self, other)

     overloads the

     /

     operator

  5. __floordiv__(self, other)

     overloads the

     [//](https://www.fiveableKeyTerm://)

     operator

  6. [__mod__](https://www.fiveableKeyTerm:__mod__)(self, other)

     overloads the

     [%](https://www.fiveableKeyTerm:%)

     operator

  7. [__pow__](https://www.fiveableKeyTerm:__pow__)(self, other)

     overloads the

     [**](https://www.fiveableKeyTerm:**)

     operator
• Implementing arithmetic operator overloading involves defining the desired magic method within the class definition
  • The method should take

    self

    and

    other

    as parameters, where

    other

    represents the object on the right-hand side of the operator (second operand)
  • Implement the desired arithmetic operation logic within the method (addition, subtraction, multiplication)
  • Return the result of the arithmetic operation (new object, modified object)

Comparison operators for user-defined objects

• Comparison operators can be overridden for custom classes by defining the corresponding magic methods
• Common comparison operator magic methods:

  1. __eq__(self, other)

     overloads the

     ==

     operator

  2. [__ne__](https://www.fiveableKeyTerm:__ne__)(self, other)

     overloads the

     !=

     operator

  3. [__lt__](https://www.fiveableKeyTerm:__lt__)(self, other)

     overloads the

     <

     operator

  4. [__le__](https://www.fiveableKeyTerm:__le__)(self, other)

     overloads the

     <=

     operator

  5. [__gt__](https://www.fiveableKeyTerm:__gt__)(self, other)

     overloads the

     >

     operator

  6. [__ge__](https://www.fiveableKeyTerm:__ge__)(self, other)

     overloads the

     >=

     operator
• Implementing comparison operator overriding involves defining the desired magic method within the class definition
  • The method should take

    self

    and

    other

    as parameters, where

    other

    represents the object being compared to (right-hand side operand)
  • Implement the comparison logic within the method (equality check, less than, greater than)
  • Return

    True

    or

    False

    based on the comparison result
• By overriding comparison operators, custom objects can be compared using the standard comparison operators
  • Enables sorting, filtering, and other comparison-based operations (sorting objects based on custom criteria, finding maximum/minimum objects)

Object-Oriented Programming Concepts

• Encapsulation: Magic methods help encapsulate the implementation details of operations, allowing objects to interact through well-defined interfaces
• Inheritance: Subclasses inherit magic methods from their parent classes, but can override them to provide specialized behavior
• Method resolution order: Determines which magic method implementation is used when multiple classes in an inheritance hierarchy define the same method
• Abstract base classes: Can define magic methods that subclasses must implement, ensuring consistent behavior across related classes