Python Membership and Identity Operators
Last Updated : 13 Feb, 2025
There is a large set of Python operators that can be used on different datatypes. Sometimes we need to know if a value belongs to a particular set. This can be done by using the Membership and Identity Operators. In this article, we will learn about Python Membership and Identity Operators.
Python Membership Operators
The Python membership operators test for the membership of an object in a sequence, such as strings, lists, or tuples. Python offers two membership operators to check or validate the membership of a value. They are as follows:
Python IN Operator
The in operator is used to check if a character/substring/element exists in a sequence or not. Evaluate to True if it finds the specified element in a sequence otherwise False.
Python # initialized some sequences list1 = [1, 2, 3, 4, 5] str1 = "Hello World" dict1 = {1: "Geeks", 2:"for", 3:"geeks"} # using membership 'in' operator # checking an integer in a list print(2 in list1) # checking a character in a string print('O' in str1) # checking for a key in a dictionary print(3 in dict1) Python NOT IN Operator
The ‘not in’ Python operator evaluates to true if it does not find the variable in the specified sequence and false otherwise.
Python # initialized some sequences list1 = [1, 2, 3, 4, 5] str1 = "Hello World" dict1 = {1: "Geeks", 2:"for", 3:"geeks"} # using membership 'not in' operator # checking an integer in a list print(2 not in list1) # checking a character in a string print('O' not in str1) # checking for a key in a dictionary print(3 not in dict1) operators.contains() Method
An alternative to Membership ‘in’ operator is the contains() function. This function is part of the Operator module in Python. The function take two arguments, the first is the sequence and the second is the value that is to be checked.
Syntax: operator.contains(sequence, value)
Example: In this code we have initialized a list, string, set, dictionary and a tuple. Then we use operator module’s contain() function to check if the element occurs in the corresponding sequences or not.
Python # import module import operator # using operator.contain() # checking an integer in a list print(operator.contains([1, 2, 3, 4, 5], 2)) # checking a character in a string print(operator.contains("Hello World", 'O')) # checking an integer in aset print(operator.contains({1, 2, 3, 4, 5}, 6)) # checking for a key in a dictionary print(operator.contains({1: "Geeks", 2:"for", 3:"geeks"}, 3)) # checking for an integer in a tuple print(operator.contains((1, 2, 3, 4, 5), 9)) OutputTrue False False True False
Python Identity Operators
The Python Identity Operators are used to compare the objects if both the objects are actually of the same data type and share the same memory location. There are different identity operators such as:
Python IS Operator
The is operator evaluates to True if the variables on either side of the operator point to the same object in the memory and false otherwise.
Python # Python program to illustrate the use # of 'is' identity operator num1 = 5 num2 = 5 a = [1, 2, 3] b = [1, 2, 3] c = a s1 = "hello world" s2 = "hello world" # using 'is' identity operator on different datatypes print(num1 is num2) print(a is b) print(a is c) print(s1 is s2) print(s1 is s2)
OutputTrue False True True True
We can see here that even though both the lists, i.e., ‘lst1’ and ‘lst2’ have same data, the output is still False. This is because both the lists refers to different objects in the memory. Where as when we assign ‘lst3’ the value of ‘lst1’, it returns True. This is because we are directly giving the reference of ‘lst1’ to ‘lst3’.
Python IS NOT Operator
The is not operator evaluates True if both variables on the either side of the operator are not the same object in the memory location otherwise it evaluates False.
Python # Python program to illustrate the use # of 'is' identity operator num1 = 5 num2 = 5 a = [1, 2, 3] b = [1, 2, 3] c = a s1 = "hello world" s2 = "hello world" # using 'is not' identity operator on different datatypes print(num1 is not num2) print(a is not b) print(a is not c) print(s1 is not s2) print(s1 is not s1)
OutputFalse True False False False
Difference between ‘==’ and ‘is’ Operator
While comparing objects in Python, the users often gets confused between the Equality operator and Identity ‘is’ operator. The equality operator is used to compare the value of two variables, whereas the identities operator is used to compare the memory location of two variables. Let us see the difference with the help of an example.
Example: In this code we have two lists that contains same data. The we used the identity ‘is’ operator and equality ‘==’ operator to compare both the lists.
Python # Python program to illustrate the use # of 'is' and '==' operators a = [1, 2, 3] b = [1, 2, 3] # using 'is' and '==' operators print(a is b) print(a == b)
Read in detail – Difference between == and is operator
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