--- title: 4.20 Common String Methods – Part 2 description: "Python provides many string methods for checking the contents of a string. These methods return **Boolean values (`True` or `False`)** based on whether a particular condition is satisfied. These methods are commonly used for validating user input, checking passwords, verifying…" url: "https://edcret.in/docs/python-programming/strings-python/4-20-common-string-methods-part-2/" updated: "2026-07-29" category: Python Programming / Strings --- # 4.20 Common String Methods – Part 2 Python provides many string methods for checking the contents of a string. These methods return **Boolean values (`True` or `False`)** based on whether a particular condition is satisfied. These methods are commonly used for validating user input, checking passwords, verifying data, and making decisions in programs. In this lesson, we will study the following commonly used string methods: - `startswith()` - `endswith()` - `isalpha()` - `isdigit()` - `isalnum()` --- ## Syntax ``` string.method(argument) ``` or ``` string.method() ``` ### Components | Component | Description | | --- | --- | | `string` | The string object. | | `.` | Dot operator used to access the method. | | `method()` | String method being called. | | `argument` | Optional value required by some methods. | --- ## Example 1: Checking the Beginning of a String **main.py** ``` text = "Python Programming" print(text.startswith("Python")) ``` ### Output ``` True ``` ### Explanation - The `startswith()` method checks whether the string begins with `"Python"`. - Since the condition is satisfied, it returns `True`. - The comparison is case-sensitive. --- ## Example 2: Checking the End of a String **main.py** ``` filename = "report.pdf" print(filename.endswith(".pdf")) ``` ### Output ``` True ``` ### Explanation - `endswith()` checks whether the string ends with `.pdf`. - Since the filename has the required extension, the result is `True`. - This method is commonly used when validating file names. --- ## Example 3: Using `isalpha()` **main.py** ``` word = "Python" print(word.isalpha()) ``` ### Output ``` True ``` ### Explanation - `isalpha()` checks whether all characters are alphabetic. - The string contains only letters. - Therefore, the result is `True`. --- ## Example 4: Using `isdigit()` **main.py** ``` number = "12345" print(number.isdigit()) ``` ### Output ``` True ``` ### Explanation - `isdigit()` checks whether every character is a digit. - Since all characters are numeric, the method returns `True`. --- ## Example 5: Using `isalnum()` **main.py** ``` text = "Python123" print(text.isalnum()) ``` ### Output ``` True ``` ### Explanation - `isalnum()` checks whether all characters are either letters or digits. - The string contains only alphabets and numbers. - Therefore, the result is `True`. --- ## Example 6: User Input Validation **main.py** ``` username = input("Enter username: ") print(username.isalnum()) ``` ### Sample Input ``` Alice123 ``` ### Output ``` True ``` ### Explanation - The user enters a username. - `isalnum()` checks whether it contains only letters and digits. - Since no special characters are present, the result is `True`. --- ## Example 7: Alphabetic Check with Spaces **main.py** ``` name = "Alice Johnson" print(name.isalpha()) ``` ### Output ``` False ``` ### Explanation - Although the string contains only letters and a space, `isalpha()` does not allow spaces. - Every character must be an alphabetic letter. - Therefore, the result is `False`. --- ## Example 8: Checking Numeric Input **main.py** ``` value = "98A7" print(value.isdigit()) ``` ### Output ``` False ``` ### Explanation - The string contains the letter `A`. - Since not every character is a digit, `isdigit()` returns `False`. --- ## Example 9: Case-Sensitive Prefix Check **main.py** ``` text = "Python" print(text.startswith("python")) ``` ### Output ``` False ``` ### Explanation - `startswith()` is case-sensitive. - `"Python"` and `"python"` are different strings. - Therefore, the result is `False`. --- ## Example 10: Checking the Result Type **main.py** ``` text = "Python" result = text.isalpha() print(result) print(type(result)) ``` ### Output ``` True ``` ### Explanation - These string methods return Boolean values. - The result is either `True` or `False`. - Therefore, the returned type is `bool`. --- # Common Mistakes ### 1. Expecting `isalpha()` to Allow Spaces **Incorrect** ``` name = "John Doe" print(name.isalpha()) ``` ### Incorrect Expectation ``` True ``` ### Actual Output ``` False ``` **Reason** Spaces are not alphabetic characters. **Correct** ``` print(name.replace(" ", "").isalpha()) ``` --- ### 2. Assuming `isdigit()` Accepts Decimal Numbers **Incorrect** ``` number = "12.5" print(number.isdigit()) ``` ### Output ``` False ``` **Reason** The decimal point (`.`) is not a digit. **Correct** ``` number = "125" print(number.isdigit()) ``` --- ### 3. Assuming `isalnum()` Allows Special Characters **Incorrect** ``` username = "Alice_123" print(username.isalnum()) ``` ### Incorrect Expectation ``` True ``` ### Actual Output ``` False ``` **Reason** The underscore (`_`) is not an alphabetic character or a digit. --- ### 4. Forgetting That `startswith()` Is Case-Sensitive **Incorrect** ``` text = "Python" print(text.startswith("python")) ``` ### Incorrect Expectation ``` True ``` ### Actual Output ``` False ``` **Reason** String comparisons performed by `startswith()` are case-sensitive. --- # Best Practices - Use `startswith()` and `endswith()` when validating filenames, URLs, and prefixes. - Use `isalpha()` to validate alphabetic input. - Use `isdigit()` before converting a numeric string using `int()`. - Use `isalnum()` when validating usernames or identification codes. - Remember that these methods return Boolean values. --- # Key Points to Remember - `startswith()` checks whether a string begins with a specified substring. - `endswith()` checks whether a string ends with a specified substring. - `isalpha()` returns `True` only if all characters are alphabetic. - `isdigit()` returns `True` only if all characters are digits. - `isalnum()` returns `True` only if all characters are letters or digits. - These methods are case-sensitive where applicable. - All these methods return values of type `bool`.