Customize your Python class with Magic or Dunder methods

Customize your Python class with Magic or Dunder methods

Magic methods, also known as dunder (short for "double underscore") methods, allow you to customize the behavior of your Python objects. They are always surrounded by double underscores (e.g., __init__, __str__).

Here's a list of some commonly used magic methods and how you can use them in your classes:

  1. Basic Customizations:

    • __init__(self, ...): Constructor method.
    • __del__(self): Destructor method. Called when the instance is about to be destroyed.
    • __repr__(self): Represents the object. Should return a valid Python expression if possible.
    • __str__(self): Called by print() and str().

  2. Comparison:

    • __eq__(self, other): Implements equality.
    • __ne__(self, other): Implements inequality.
    • __lt__(self, other): Implements less than.
    • __le__(self, other): Implements less than or equal to.
    • __gt__(self, other): Implements greater than.
    • __ge__(self, other): Implements greater than or equal to.

  3. Arithmetic:

    • __add__(self, other): Implements addition.
    • __sub__(self, other): Implements subtraction.
    • __mul__(self, other): Implements multiplication.
    • ... and other arithmetic operators like __floordiv__, __mod__, __pow__, etc.

  4. Type Conversion:

    • __int__(self): Implements type conversion to int.
    • __float__(self): Implements type conversion to float.
    • __bool__(self): Implements type conversion to bool. If not defined, objects are always True unless they define a __len__ method that returns False or 0.

  5. Containers:

    • __len__(self): Implements the built-in function len().
    • __getitem__(self, key): Implements accessing an item using obj[key].
    • __setitem__(self, key, value): Implements setting an item using obj[key] = value.
    • __delitem__(self, key): Implements deleting an item using del obj[key].
    • __iter__(self): Implements iteration over the container.
    • __contains__(self, item): Implements membership test operators (in and not in).

Here's an example of a class that uses some of these magic methods:

class ComplexNumber: def __init__(self, real, imag): self.real = real self.imag = imag def __repr__(self): return f"ComplexNumber({self.real}, {self.imag})" def __str__(self): return f"{self.real} + {self.imag}i" def __add__(self, other): return ComplexNumber(self.real + other.real, self.imag + other.imag) def __eq__(self, other): return self.real == other.real and self.imag == other.imag # Usage: c1 = ComplexNumber(3, 2) c2 = ComplexNumber(1, 7) print(c1) # 3 + 2i print(c1 + c2) # 4 + 9i print(c1 == c2) # False

These are just a few examples. There are many more magic methods available in Python that allow you to define custom behavior for your objects in various scenarios.

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