all Python 3OOPfunction

__eq__

magic methods

The method behind ==. Without it two objects are equal only when they are the same object, as with is.

Syntax

def __eq__(self, other): ...

Defining __eq__ removes __hash__: instances can no longer go into a set or serve as dict keys until a __hash__ consistent with equality is defined too. Python 3 derives != itself by inverting __eq__. For a foreign type return NotImplemented rather than False, so Python asks the other operand.

Examples

class Point:
    def __init__(self, x, y):
        self.x, self.y = x, y
    def __eq__(self, other):
        if not isinstance(other, Point):
            return NotImplemented
        return (self.x, self.y) == (other.x, other.y)
print(Point(1, 2) == Point(1, 2))  # → True
print(Point(1, 2) != Point(3, 4))  # → True — != выведен из __eq__
print(Point.__hash__)  # → None — без __hash__ в set не положить

See also

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