L4·OOP & Errors

✨Dunder Methods

__methods__ that hook into Python's syntax.

dunder__str____eq____len__

§ 1The Big Ones

__init__, __repr__, __str__, __eq__, __hash__, __len__, __getitem__, __iter__, __call__, __enter__/__exit__.

§ 2Operator overloading

__add__, __mul__, __lt__ etc. — a + b calls a.__add__(b) or b.__radd__(a).

Example

1class Vector:
2    def __init__(self, x, y):
3        self.x, self.y = x, y
4    def __add__(self, other):
5        return Vector(self.x+other.x, self.y+other.y)
6    def __repr__(self):
7        return f"Vector({self.x}, {self.y})"
8
9print(Vector(1,2) + Vector(3,4))

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Question 1 / 2

Which dunder makes len(obj) work?

Inheritance & MRO

Properties & Descriptors