python-object-equivalence.py

# https://stackoverflow.com/questions/390250/elegant-ways-to-support-equivalence-equality-in-python-classes

class Number:

	def __init__(self, number):
		self.number = number

	def __eq__(self, other):
		"""Overrides the default implementation"""
		if isinstance(other, Number):
			return self.number == other.number
		return NotImplemented

	def __hash__(self):
		"""Overrides the default implementation"""
		return hash(tuple(sorted(self.__dict__.items())))


class SubNumber(Number):
	pass


n1 = Number(1)
n2 = Number(1)
n3 = SubNumber(1)
n4 = SubNumber(4)

assert n1 == n2
assert n2 == n1
assert not n1 != n2
assert not n2 != n1

assert n1 == n3
assert n3 == n1
assert not n1 != n3
assert not n3 != n1

assert not n1 == n4
assert not n4 == n1
assert n1 != n4
assert n4 != n1

assert len(set([n1, n2, n3, ])) == 1
assert len(set([n1, n2, n3, n4])) == 2