PythonIdentity and Membership Operators

Membership and Identity Operators in Python

Python provides two special types of operators:

  1. Membership Operators: Test whether a value is part of a sequence (such as string, list, tuple, or set).
  2. Identity Operators: Compare the memory locations of two objects.

These operators help write clean, readable, and efficient code when checking for existence or object identity.

1. Membership Operators

OperatorDescription
inReturns True if a value is present in a sequence
not inReturns True if a value is NOT present in a sequence

Example 1: Using in with a List

membership_in_list.py
fruits = ["apple", "banana", "cherry"]
print("banana" in fruits)
output.txt
True

Example 2: Using not in with a String

membership_not_in_string.py
sentence = "Python is fun"
print("Java" not in sentence)
output.txt
True

Explanation:

  • in checks if the value is in the sequence (string, list, tuple, set, or dictionary keys).
  • not in checks if the value is absent.

2. Identity Operators

OperatorDescription
isReturns True if two variables point to the same object in memory
is notReturns True if two variables do NOT point to the same object

Example 1: Using is with Variables

identity_is.py
x = [1, 2, 3]
y = x
print(x is y)
output.txt
True

Explanation:

  • y points to the same object as x.
  • is compares identity, not just value.

Example 2: is not with Separate Objects

identity_is_not.py
x = [1, 2, 3]
y = [1, 2, 3]
print(x is not y)
output.txt
True

Explanation:

  • Even though x and y have the same value, they are different objects.
  • Their identity (memory location) is different.

Example 3: Using is with Immutable Objects (Integers)

identity_integers.py
a = 100
b = 100
print(a is b)
output.txt
True

Explanation:

  • For small integers (typically between -5 and 256), Python caches objects.
  • So a and b may point to the same object.

Example 4: is with Strings

identity_strings.py
s1 = "hello"
s2 = "hello"
print(s1 is s2)
output.txt
True

Explanation:

  • Short string literals are often cached by Python.
  • is may return True for such strings.

Summary

  • Membership Operators:

    • in: Checks if a value exists in a sequence.
    • not in: Checks if a value does not exist.

  • Identity Operators:

    • is: Checks if two references point to the same object.
    • is not: Checks if they do not.

  • Use cases:

    • Membership: Useful for searching within collections.
    • Identity: Useful for checking object identity (especially when working with mutable objects, None, or singleton patterns).
Bitwise OperatorsOperator Precedence