--- title: 2.13 Keywords and Identifiers description: "Python programs are made up of different kinds of names. These names are called **identifiers**. An **identifier** is the name given to variables, functions, classes, modules, and other objects in a Python program. Some names, however, are reserved by Python…" url: "https://edcret.in/docs/python-programming/basic-refreshers-python/2-13-keywords-and-identifiers/" updated: "2026-07-29" category: Python Programming / Basic Refreshers --- # 2.13 Keywords and Identifiers Python programs are made up of different kinds of names. These names are called **identifiers**. An **identifier** is the name given to variables, functions, classes, modules, and other objects in a Python program. Some names, however, are reserved by Python itself. These reserved words are called **keywords**. Understanding the difference between keywords and identifiers is essential because keywords cannot be used as identifiers. --- ## What are Keywords? Keywords are reserved words that have predefined meanings in Python. Examples include: - `if` - `else` - `for` - `while` - `break` - `continue` - `return` - `def` - `class` - `import` - `True` - `False` - `None` Python uses these words to define the language syntax. --- ## Example 1: Displaying Python Keywords **main.py** ``` import keyword print(keyword.kwlist) ``` ### Sample Output ``` ['False', 'None', 'True', 'and', 'as', 'assert', 'async', 'await', 'break', 'class', 'continue', 'def', 'del', 'elif', 'else', 'except', 'finally', 'for', 'from', 'global', 'if', 'import', 'in', 'is', 'lambda', 'nonlocal', 'not', 'or', 'pass', 'raise', 'return', 'try', 'while', 'with', 'yield', ...] ``` ### Explanation - The `keyword` module contains information about Python keywords. - `keyword.kwlist` returns a list of all reserved keywords. - The exact list may vary slightly depending on the Python version. --- ## Example 2: Checking Whether a Word is a Keyword **main.py** ``` import keyword print(keyword.iskeyword("for")) print(keyword.iskeyword("student")) ``` ### Output ``` True False ``` ### Explanation - `keyword.iskeyword()` checks whether a word is a Python keyword. - `"for"` is a reserved keyword, so the result is `True`. - `"student"` is not a keyword, so the result is `False`. --- ## Example 3: Valid Identifiers **main.py** ``` student_name = "Alice" age = 20 _marks = 95 print(student_name) print(age) print(_marks) ``` ### Output ``` Alice 20 95 ``` ### Explanation - `student_name`, `age`, and `_marks` are valid identifiers. - They follow Python's naming rules. - These names are descriptive and easy to understand. --- ## Example 4: Identifier Names are Case-Sensitive **main.py** ``` name = "Alice" Name = "Bob" print(name) print(Name) ``` ### Output ``` Alice Bob ``` ### Explanation - `name` and `Name` are different identifiers. - Python treats uppercase and lowercase letters as different characters. - Identifiers are case-sensitive. --- ## Example 5: Function Names are Identifiers **main.py** ``` def greet(): print("Welcome!") greet() ``` ### Output ``` Welcome! ``` ### Explanation - `greet` is the name of a function. - Function names are identifiers. - Python uses the identifier to call the function. --- ## Example 6: Class Names are Identifiers **main.py** ``` class Student: pass print(Student) ``` ### Sample Output ``` ``` ### Explanation - `Student` is the identifier of the class. - Class names are also identifiers. - By convention, class names use **PascalCase**. --- ## Example 7: Module Names are Identifiers **main.py** ``` import math print(math.pi) ``` ### Output ``` 3.141592653589793 ``` ### Explanation - `math` is the identifier of the imported module. - After importing the module, its members can be accessed using the dot (`.`) operator. --- ## Example 8: Using Meaningful Identifiers **main.py** ``` employee_salary = 45000 print(employee_salary) ``` ### Output ``` 45000 ``` ### Explanation - `employee_salary` clearly describes the stored value. - Meaningful identifiers improve readability and maintainability. --- ## Example 9: Identifiers Can Contain Digits **main.py** ``` student1 = "Alice" student2 = "Bob" print(student1) print(student2) ``` ### Output ``` Alice Bob ``` ### Explanation - Digits are allowed in identifiers. - However, an identifier cannot begin with a digit. --- ## Example 10: Different Types of Identifiers **main.py** ``` PI = 3.14159 radius = 5 area = PI * radius * radius print(area) ``` ### Output ``` 78.53975 ``` ### Explanation - `PI`, `radius`, and `area` are all identifiers. - They represent different values in the program. - Good identifiers make code easier to understand. --- # Common Mistakes ### 1. Using a Keyword as an Identifier **Incorrect** ``` for = 10 ``` ### Output ``` SyntaxError: invalid syntax ``` **Reason** `for` is a reserved keyword and cannot be used as an identifier. **Correct** ``` count = 10 ``` --- ### 2. Starting an Identifier with a Digit **Incorrect** ``` 2value = 50 ``` ### Output ``` SyntaxError: invalid decimal literal ``` **Reason** Identifiers cannot begin with digits. **Correct** ``` value2 = 50 ``` --- ### 3. Using Special Characters **Incorrect** ``` student@name = "Alice" ``` ### Output ``` SyntaxError: invalid syntax ``` **Reason** Special characters such as `@`, `$`, and `%` are not allowed in identifiers. --- ### 4. Using Meaningless Names **Poor Practice** ``` x = 45000 ``` **Better Practice** ``` employee_salary = 45000 ``` **Reason** Meaningful identifiers make programs easier to understand and maintain. --- # Best Practices - Use descriptive names for variables, functions, and classes. - Never use Python keywords as identifiers. - Follow the `snake_case` naming convention for variables and functions. - Use `PascalCase` for class names. - Keep identifier names clear and meaningful. --- # Key Points to Remember - An identifier is the name given to a program element such as a variable, function, class, or module. - Keywords are reserved words with predefined meanings in Python. - Keywords cannot be used as identifiers. - Identifiers are case-sensitive. - Identifiers must follow Python's naming rules. - Use meaningful names to improve code readability. - The `keyword` module can be used to view and check Python keywords.