magicmethods.md

Magic Methods (dunder methods) [Readability, Programming Efficiency]

Detectors

• Github.com

What is it?

These are considered special methods used to override default behavior in Python that, as the docs describe, are invoked by special syntax (such as +, -, >, <) [1].

Example

class Person:
    def __init__(self, name, age):
        self.age = age
        self.name = name
    
    def __gt__(self, other):
        return self.age > other.age
    
    def __eq__(self, other):
        return self.age == other.age and self.name == other.name

>>> p1 = Person("Aamir", 21)
>>> p2 = Person("Abdullah", 20)
>>> p1 > p2
True
>>> p1 == p2
False

`functools.total_ordering

This is a decorator which, by definining one of the __lt__(), __le__(), __gt__(), or __ge__(), in addition to the __eq__() magic methods, it can implicitly define all of the remaining comparison magic methods. We can improve the above example...

from functools import total_ordering

@total_ordering
class Person:
    ...
    
    def __gt__(self, other):
        return self.age > other.age
    
    def __eq__(self, other):
        return self.age == other.age and self.name == other.name

>>> p1 = Person("Aamir", 21)
>>> p2 = Person("Abdullah", 20)
>>> p1 > p2
True
>>> p1 <= p2 # We didn't explicitly define this behavior
False

References

[1] Python docs -- Special method names
[2] Python docs -- Special method names

Books that mention this topic:

[3] Python Tricks: A Buffet of Awesome Python Features by Dan Bader
[4] Python Cookbook, Third Edition by David Beazley and Brian K. Jones