Functions and Objects · Objects · lesson 9 of 10

Dunder methods

about 15 minutes · free · runs in your browser

Making your objects behave like built-in ones

Methods named with double underscores — "dunder" methods — hook your class into Python's own syntax.

Method	Called by
`__init__`	creating an instance
`__str__`	`print(obj)` and `str(obj)`
`__repr__`	the console, and debugging
`__eq__`	`a == b`
`__len__`	`len(obj)`

class Point:
    def __init__(self, x, y):
        self.x, self.y = x, y

    def __str__(self):
        return f"({self.x}, {self.y})"

    def __eq__(self, other):
        return self.x == other.x and self.y == other.y

Without __eq__, Point(1, 2) == Point(1, 2) is False — Python falls back to comparing identity, and they are two different objects.

Your turn: give Playlist a __str__ reading "Road Trip (3 tracks)", a __len__ returning the track count, and an __eq__ comparing names and tracks.

You start from this, and edit it in the browser:

class Playlist:
    def __init__(self, name, tracks):
        self.name = name
        self.tracks = tracks

    def __str__(self):
        pass

    def __len__(self):
        pass

    def __eq__(self, other):
        pass