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 i
s
n
o
t
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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