__hash__ — Easy Examples

Returns the hash value; required for dict key or set member

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Implementing __hash__

Basic implementation of __hash__ in a class.

python
class Color:
    def __init__(self, r, g, b):
        self.r = r
        self.g = g
        self.b = b

    def __hash__(self):
        return hash((self.r, self.g, self.b))

    def __eq__(self, other):
        return (self.r, self.g, self.b) == (other.r, other.g, other.b)

colors = {Color(255, 0, 0): "red", Color(0, 255, 0): "green"}
print(colors[Color(255, 0, 0)])

__hash__ returns the hash value; required for dict key or set member. Implementing it lets you customize how Python interacts with your objects.

__hash__ in action

Seeing __hash__ called by Python's built-in operations.

python
# How Python calls __hash__ automatically
class Demo:
    def __init__(self, value):
        self.value = value

    def __hash__(self):
        print(f"__hash__ was called!")
        return self

d = Demo(42)
# This triggers __hash__:
print(hash(d))

Python automatically calls __hash__ when you use the corresponding operator or function on your object.

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