Python Membership & Identity Operators

What Are Membership & Identity Operators?

Python provides special operators that allow us to answer two important questions:

1. Membership: Does this value exist inside another object?
2. Identity: Are these two variables referring to the exact same object?

Python has four operators for these purposes:

# Membership
in
not in

# Identity
is
is not

The in Operator

The in operator checks whether a value exists inside another object.

It returns either True or False.

numbers = [10, 20, 30, 40]

print(20 in numbers)
print(50 in numbers)

True
False

Python searches the collection and checks whether the specified value is present.

The not in Operator

The not in operator checks whether a value does not exist inside an object.

numbers = [10, 20, 30]

print(40 not in numbers)
print(20 not in numbers)

True
False

Membership with Strings

Membership operators can also be used with strings. Python checks whether one string occurs inside another string.

text = "Python Programming"

print("Python" in text)
print("Programming" in text)
print("Java" in text)
print("Java" not in text)

True
True
False
True

text = "Python"

print("Python" in text)
print("python" in text)

Membership with Lists

Lists are one of the most common places where membership operators are used.

students = ["Ali", "Sara", "Ahmed", "Fatima"]

print("Sara" in students)
print("Hamza" in students)
print("Ahmed" not in students)

True
False
False

This becomes particularly useful when validating user selections or checking whether an item already exists.

Membership with Tuples

Membership operators work with tuples in the same way they work with lists.

days = ("Monday", "Tuesday", "Wednesday")

print("Monday" in days)
print("Friday" in days)
print("Sunday" not in days)

True
False
True

Membership with Sets

Sets are especially useful when you frequently need membership checks.

numbers = {10, 20, 30, 40, 50}

print(30 in numbers)
print(100 in numbers)
print(100 not in numbers)

True
False
True

Because sets are designed around unique elements and membership operations, they are often useful for fast existence checks.

Membership with Dictionaries

Dictionaries require special attention. When you use in with a dictionary, Python checks the keys by default.

student = {
    "name": "Ali",
    "age": 25,
    "city": "Multan"
}

print("name" in student)
print("age" in student)
print("Ali" in student)

True
True
False

"name" in student     # True
"Ali" in student      # False

If you want to check dictionary values, you can use .values().

student = {
    "name": "Ali",
    "age": 25
}

print("Ali" in student.values())
print(25 in student.values())

True
True

Practical Membership Examples

Membership operators become powerful when combined with conditions.

Checking an Allowed Role

allowed_roles = ["admin", "manager", "editor"]

role = "manager"

if role in allowed_roles:
    print("Access granted")
else:
    print("Access denied")

Access granted

Checking an Email Domain

email = "student@example.com"

if "@example.com" in email:
    print("Valid example domain")
else:
    print("Different domain")

Checking a Product Category

categories = ["shoes", "shirts", "bags"]

product_category = "shoes"

if product_category in categories:
    print("Category available")

The is Operator

The is operator checks whether two variables refer to the same object.

This is different from checking whether two values are equal.

a = [1, 2, 3]
b = a

print(a is b)

True

Both a and b refer to the same list object.

The is not Operator

The is not operator checks whether two variables refer to different objects.

a = [1, 2, 3]
b = [1, 2, 3]

print(a is not b)

True

Although the lists contain the same values, they are two separate list objects.

is vs ==

This is one of the most important distinctions in Python.

a = [1, 2, 3]
b = [1, 2, 3]

print(a == b)
print(a is b)

True
False

a = [1, 2, 3]
b = a

print(a == b)
print(a is b)

True
True

Identity and Object References

To understand is, it helps to understand that variables in Python refer to objects.

numbers = [10, 20, 30]

another = numbers

print(numbers is another)

True

The statement:

another = numbers

does not create a new list. Both variable names refer to the same list object.