Python __ne__ Magic Method

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To customize the behavior of the non-equality operator x != y, override the __ne__() dunder method in your class definition. Python internally calls x.__ne__(y) to compare two objects using x != y. If the __ne__() method is not defined, Python will use the is not operator per default that checks for two arbitrary objects whether they reside on a different memory address.

Syntax

__ne__(self, other)

To use the not equal to operator on custom objects, define the __ne__() “dunder” magic method that takes two arguments: self and other. You can then use attributes of the custom objects to determine if one is not equal to the other. It should return a Boolean True or False.

Let’s have a look at an example next.

Example

In the following code, you check if a Person is not equal to another Person by using the age attribute as a decision criterion:

class Person:
    def __init__(self, age):
        self.age = age

    def __ne__(self, other):
        return self.age != other.age



alice = Person(18)
bob = Person(19)
carl = Person(18)

print(alice != bob)
# True

print(alice != carl)
# False

Because Alice is 18 years old and Bob is 19 years old, and 18 != 19 is True, the result of alice != bob is True. But the result of alice != carl evaluates to False as both have the same age.

Background Video

Default Implementation of __ne__

Per default, the __ne__() dunder method is implemented using the is not identity operator. Identity operators are used to check whether two values or variables reside at a different memory location, i.e., refer to a different object in memory.

Because the fallback identity operator is defined for each object, you can also check non-equality for any two objects.

The following example shows that you can compare custom persons using the non-equality operator !=, even without defining the __ne__ method. Internally, Python uses the non-identity operator:

class Person:
    def __init__(self, age):
        self.age = age



alice = Person(18)
bob = Person(19)
carl = Person(18)

print(alice != bob)
# True

print(alice != carl)
# True

print(alice != alice)
# False

Background Video Identity Operator

To understand the identity operator, feel free to watch the following background video:

Commutativity of Non-Equality !=

The output of x != y and y != x may be different because the former calls x.__ne__(y) and the latter calls y.__ne__(x). If x and y have different definitions of the dunder method __ne__(), the operation becomes non-commutative.

You can see this in the following example:

class Person:
    def __ne__(self, other):
        return 42


class Human:
    def __ne__(self, other):
        return 0


alice = Person()
bob = Human()


print(alice != bob)
# 42

print(bob != alice)
# 0

Where to Go From Here?

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