Identity and Membership Operators (is, in) in Python

Python has two types of operators, which are used to compare objects and find a value in things like a list, string, or set.

They are:

• Identity Operators (is, is not)
• Membership Operators (in, not in)

1. Identity Operators (is, is not)

Identity operators check whether two variables are pointing to the same object in memory or not.

They do not compare values; they just check whether both have the same address or not.

• is → Returns True if both variables are pointing to the same object.
• is not → Returns True if both are pointing to different objects.

Example:

list1 = [1, 2, 3]
list2 = [1, 2, 3]
list3 = list1 # list3 and list1 are the same object

print(list1 is list2)      # False - different objects
print(list1 is list3)      # True - same object
print(list1 is not list2)  # True

An important thing:

If you want to check if a variable is None or not, then using is None is the best and fastest way.

Remember:

• If you want to compare values then use ==.
• If you want to check if both are exactly the same object then use is.

2. Membership Operators (in, not in)

These operators check whether a value is in a sequence (such as a list, string, tuple, or set) or not.

• in → Returns True if the value is found in the sequence.
• not in → Returns True if the value is not found in the sequence.

Example 1: List and String

fruits = ["apple", "banana", "cherry"]
text = "Hello Python"

print("apple" in fruits)      # True
print("grape" not in fruits)  # True
print("Python" in text)       # True

The in operator can find substrings in a string, and also elements in a list/tuple.

Example 2: Dictionary

With a dictionary, the in operator finds keys, not values.

data = {"a": 1, "b": 2}

print("a" in data)           # True - key exists
print(1 in data)             # False - does not check values by default
print(1 in data.values())    # True - values() has to be used to check values

3. Understand the difference quickly

Next Lession: if, elif, else Conditions in Python

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