How to use the "in" and "not in" Operators in Python

Python is a popular programming language due to how readable and straightforward the syntax and keywords are.

A great example of this is the in and not in operators, which have many uses in Python.

In this post, we'll learn how to use the in and not in operators in Python.

How to use the in and not in operators with lists

A list in Python is a collection of items in a particular order. You can define a list by placing all the items inside square brackets [], separated by commas.

	fruits = ["apple", "banana", "cherry"]

Now, we can use the in operator to check if an item is in a list.

	fruits = ["apple", "banana", "cherry"]

if "apple" in fruits:
    print("Yes, 'apple' is in the fruits list")

	Yes, 'apple' is in the fruits list

Alternatively, we can use the not in operator to check if an item is not in a list.

	fruits = ["apple", "banana", "cherry"]

if "pineapple" not in fruits:
    print("No, 'pineapple' is not in the fruits list")

	No, 'pineapple' is not in the fruits list

How to use the in and not in operators with strings

Internally, a string in Python is basically a sequence of characters. You can define a string by placing all the characters inside single quotes '' or double quotes "".

	sentence = "The quick brown fox jumps over the lazy dog"

Now, we can use the in operator to check if a substring is in a string.

	sentence = "The quick brown fox jumps over the lazy dog"

if "quick" in sentence:
    print("Yes, 'quick' is in the sentence")

	Yes, 'quick' is in the sentence

Likewise, we can use the not in operator to check if a substring is not in a string.

	sentence = "The quick brown fox jumps over the lazy dog"

if "quickly" not in sentence:
    print("No, 'quickly' is not in the sentence")

	No, 'quickly' is not in the sentence

How to use the in and not in operators with dictionaries

In Python, a dictionary is a collection of key-value pairs. You can define a dictionary by placing all the key-value pairs inside curly braces {}, separated by commas.

	person = {
    "name": "John",
    "age": 36,
    "country": "Norway"
}

Now, we can use the in operator to check if a key is in a dictionary.

	person = {
    "name": "John",
    "age": 36,
    "country": "Norway"
}

if "name" in person:
    print("Yes, 'name' is one of the keys in the person dictionary")

	Yes, 'name' is one of the keys in the person dictionary

On the other hand, we can use the not in operator to check if a key is not in a dictionary.

	person = {
    "name": "John",
    "age": 36,
    "country": "Norway"
}

if "email" not in person:
    print("No, 'email' is not one of the keys in the person dictionary")

	No, 'email' is not one of the keys in the person dictionary

Conclusion

In this post, we learned how to use the in and not in operators in Python.

These operators are useful for checking if an item is in a list, a substring is in a string, or a key is in a dictionary.

Thanks for reading!

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