237 – __eq__

The dunder method __eq__ implements equality comparison. Implement it to override the default behaviour, which behaves like the keyword is and only checks for identity equality:

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

p1 = Coords(2, 3)
p2 = Coords(2, 3)
print(p1 == p2)  # False ?!

If you implement __eq__, you can say that two objects Coords with the same attributes x and y are equal:

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

  def __eq__(self, other):
    if isinstance(other, Coords):
      return self.x == other.x and self.y == other.y
    return NotImplemented

p1 = Coords(2, 3)
p2 = Coords(2, 3)
print(p1 == p2)  # True :)

Note that the correct way to implement __eq__ is to return NotImplemented for types that you don’t care about or don’t know about.