--- title: 4.14 Membership Operators description: "Membership operators are used to check whether a character or substring exists within a string. Python provides two membership operators: - `in` - `not in` The `in` operator returns `True` if the specified character or substring is present in the…" url: "https://edcret.in/docs/python-programming/strings-python/4-14-membership-operators/" updated: "2026-07-29" category: Python Programming / Strings --- # 4.14 Membership Operators Membership operators are used to check whether a character or substring exists within a string. Python provides two membership operators: - `in` - `not in` The `in` operator returns `True` if the specified character or substring is present in the string. The `not in` operator returns `True` if the specified character or substring is absent. Membership operators are commonly used for searching text, validating user input, checking keywords, and making decisions in programs. --- ## Syntax ``` substring in string_name ``` or ``` substring not in string_name ``` ### Components | Component | Description | | --- | --- | | `substring` | Character or sequence of characters to search for. | | `in` | Returns `True` if the substring exists. | | `not in` | Returns `True` if the substring does not exist. | | `string_name` | The string being searched. | --- ## Example 1: Using the `in` Operator **main.py** ``` text = "Python Programming" print("Python" in text) ``` ### Output ``` True ``` ### Explanation - Python searches for the substring `"Python"`. - The substring exists in the string. - Therefore, the result is `True`. --- ## Example 2: Using the `not in` Operator **main.py** ``` text = "Python Programming" print("Java" not in text) ``` ### Output ``` True ``` ### Explanation - Python searches for `"Java"`. - The substring is not found. - Therefore, `not in` returns `True`. --- ## Example 3: Searching for a Character **main.py** ``` word = "Computer" print("m" in word) ``` ### Output ``` True ``` ### Explanation - Membership operators work with single characters as well. - The character `"m"` exists in `"Computer"`. - Therefore, the result is `True`. --- ## Example 4: Case-Sensitive Search **main.py** ``` text = "Python" print("python" in text) ``` ### Output ``` False ``` ### Explanation - Membership operations are case-sensitive. - `"Python"` and `"python"` are different strings. - Therefore, the result is `False`. --- ## Example 5: Searching for a Word **main.py** ``` sentence = "Python is easy to learn." print("easy" in sentence) ``` ### Output ``` True ``` ### Explanation - Python searches for the substring `"easy"`. - The word is found in the sentence. - Therefore, the result is `True`. --- ## Example 6: User Input **main.py** ``` email = input("Enter your email: ") print("@" in email) ``` ### Sample Input ``` alice@example.com ``` ### Output ``` True ``` ### Explanation - The user enters an email address. - The program checks whether it contains the `@` character. - Since it exists, the result is `True`. --- ## Example 7: Searching for a Numeric String **main.py** ``` number = "987654321" print("654" in number) ``` ### Output ``` True ``` ### Explanation - `"654"` is treated as a substring. - Python finds it within the string. - Therefore, the result is `True`. --- ## Example 8: Using `not in` **main.py** ``` word = "Python" print("z" not in word) ``` ### Output ``` True ``` ### Explanation - Python searches for the character `"z"`. - It is not found. - Therefore, `not in` returns `True`. --- ## Example 9: Case-Insensitive Membership Test **main.py** ``` text = "Python Programming" print("python" in text.lower()) ``` ### Output ``` True ``` ### Explanation - `lower()` converts the entire string to lowercase. - `"python"` is then searched in the lowercase string. - This performs a case-insensitive membership test. --- ## Example 10: Checking the Result Type **main.py** ``` result = "Py" in "Python" print(result) print(type(result)) ``` ### Output ``` True ``` ### Explanation - Membership operators return either `True` or `False`. - Therefore, the result is of type `bool`. --- # Common Mistakes ### 1. Assuming Membership Checks Ignore Case **Incorrect** ``` print("python" in "Python") ``` ### Incorrect Expectation ``` True ``` ### Actual Output ``` False ``` **Reason** Membership operators are case-sensitive. **Correct** ``` print("python" in "Python".lower()) ``` --- ### 2. Confusing Characters with Numbers **Incorrect** ``` print(5 in "12345") ``` ### Output ``` TypeError: 'in ' requires string as left operand, not int ``` **Reason** The left operand must be a string when searching within another string. **Correct** ``` print("5" in "12345") ``` --- ### 3. Expecting `in` to Return the Position **Incorrect** ``` print("Py" in "Python") ``` ### Incorrect Expectation ``` 0 ``` ### Actual Output ``` True ``` **Reason** The `in` operator only checks for existence. It does not return the position of the substring. --- ### 4. Assuming Only Whole Words Can Be Found **Incorrect** ``` print("gram" in "Programming") ``` ### Incorrect Expectation ``` False ``` ### Actual Output ``` True ``` **Reason** Membership operators search for any matching substring, not just complete words. --- # Best Practices - Use `in` to check whether a substring exists before processing it. - Remember that membership operations are case-sensitive. - Use `lower()` or `upper()` for case-insensitive searches. - Use descriptive variable names for the string and the substring being searched. - Use `not in` when checking that a substring is absent. --- # Key Points to Remember - Python provides the `in` and `not in` membership operators. - `in` returns `True` if a substring exists in a string. - `not in` returns `True` if a substring does not exist. - Membership operations are case-sensitive. - They work with both characters and substrings. - The result is always of type `bool`. - Membership operators check for existence, not the position of the substring.