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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.

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:

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.

# 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)

The 'not in' Python operator evaluates to true if it does not find the variable in the specified sequence and false otherwise.

# 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)

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.

# 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))

True
False
False
True
False

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:

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 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)

True
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'.

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 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)

False
True
False
False
False

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 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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