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# Membership Operator in Python

Last Updated on April 27, 2023 by Prepbytes

The membership operators are useful for quickly checking whether a particular value is present in a large dataset, and they can also be used in control statements to perform different actions based on the presence or absence of a specific element. In this article, we will discuss what membership operators in Python are, how they work, and provide some examples to help you understand them better.

## What is a Membership Operator?

Membership operators in Python are operators used to test whether a value exists in a sequence, such as a list, tuple, or string. The membership operators available in Python are,

• in: The in operator returns True if the value is found in the sequence.
• not in: The not in operator returns True if the value is not found in the sequence

Membership operators are commonly used with sequences like lists, tuples, and sets. They can also be used with strings, dictionaries, and other iterable objects.

Membership operators are useful in scenarios where you need to check whether a value exists in a sequence or not. By using the in or not in operator, you can easily check whether a value is present in a sequence or not, without having to loop through the entire sequence.

Membership operators in Python are commonly used with sequences like lists, tuples, and sets. They can also be used with strings, dictionaries, and other iterable objects.

### Example of Membership Operator in Python

Let’s have a better understanding of the membership operators in Python with the help of the following code.

```# membership operator in Python
# using "in" operator
fruits = ["apple", "banana", "cherry"]
if "banana" in fruits:
print("Yes, banana is a fruit!")
# using "not in" operator
if "orange" not in fruits:
print("Yes, orange is not in the list of fruits")```

Output:

``````Yes, banana is a fruit!
Yes, orange is not in the list of fruits``````

Explanation:
In the example above, the in membership operator is used to check if "banana" is a member of the fruits list, and the not in operator is used to check if "orange" is not a member of the fruits list.

## Types of Membership Operators in Python

There are two membership operators in Python i.e., "in" and "not in".

• The "in" operator is used to test whether a value is a member of a sequence. It returns True if the specified value is found in the sequence and False otherwise. The "in" operator can be used with sequences like lists, tuples, strings, sets, and dictionaries.
• The "not in" operator is used to test whether a value is not a member of a sequence. It returns True if the specified value is not found in the sequence and False otherwise. The "not in" operator can also be used with sequences like lists, tuples, strings, sets, and dictionaries.

### Difference between ‘in’ and ‘not in’ Membership Operators

The primary distinction between the ‘in’ and ‘not in’ operators is that the ‘in’ checks whether a value exists within a sequence, whereas the ‘not in’ checks whether a value does not exist within a sequence. In other words, the ‘in’ operator verifies the presence of a given value, while the ‘not in’ operator verifies its absence in the sequence.

Here are some examples to illustrate the difference between ‘in’ and ‘not in’ membership operators.

Example of Using ‘in’ Operator in Python
Below we have a code example that shows the working of the in operator in Python.

Code Implementation:

``````fruits = ['apple', 'banana', 'orange']
if 'banana' in fruits:
print("Yes, 'banana' is a fruit!")``````

Output:

``Yes, 'banana' is a fruit!``

Explanation:
In this example, the ‘in’ operator checks whether the value ‘banana’ is present in the list of fruits. Since ‘banana’ is present in the list, the condition is True, and the message is printed.

Example of Using ‘not in’ Operator in Python
The following code shows the usage of the ‘not in’ operator in Python.

Code Implementation:

``````fruits = ['apple', 'banana', 'orange']
if 'grape' not in fruits:
print("No, 'grape' is not a fruit!")``````

Output:

``No, 'grape' is not a fruit!``

Explanation:
In this example, the ‘not in’ operator checks whether the value ‘grape’ is not present in the list of fruits. Since ‘grape’ is not present in the list, the condition is True, and the message is printed.

## Application of Membership Operators in Python

The membership operator is widely used in various fields, including mathematics, computer science, and artificial intelligence. Here are some examples of its applications:

• Set theory: The membership operator is used to define sets and determine the membership of elements in the set. It is a fundamental concept in set theory that is used to perform set operations such as union, intersection, and complement.
• Programming languages: The membership operator is used in programming languages to test whether a value is a member of a list or a tuple. For example, in Python, the ‘in’ keyword is used to test the membership of an element in a list or a tuple.
• Database management: The membership operator is used in database management to perform operations on sets of data. It is used to filter data and retrieve records that meet a specific condition.
• Artificial intelligence: The membership operator is used in fuzzy logic to represent the degree of membership of an element in a set. Fuzzy logic is used to model systems that have uncertain or imprecise information.
• Natural language processing: The membership operator is used in natural language processing to determine the similarity between words and phrases. It is used to identify synonyms and related words in a corpus of text.

Conclusion
In conclusion, the membership operators in and not in are essential tools for testing whether a value or element is present in a sequence in Python. These operators allow us to quickly and easily check for the existence of a particular value or element in a dataset and can be used in various control statements to perform different actions based on the presence or absence of specific elements. Overall, the membership operator in Python is a simple yet powerful tool in Python for testing membership in sequences and can help to streamline code and increase efficiency.

Here are some frequently asked questions related to membership operator in Python.

Ques 1. Can the membership operators be used with dictionaries in Python?
Ans. Yes, the membership operators can be used with dictionaries in Python. They test whether a key is present in the dictionary.

Ques 2. Can the membership operators be used with custom classes in Python?
Ans. Yes, the membership operators can be used with custom classes in Python. You need to define the "contains()" method in your class to specify the membership behavior.

Ques 3. Can we use the "in" membership operator with a None object in Python?
Ans. No, we cannot use the "in" operator with a None object in Python, If we do so we will get a TypeError since None is not iterable.

Ques 4. Can the membership operators be used with other operators in Python?
Ans. Yes, the membership operators can be used with other operators in Python.