What are Identifiers?

Identifiers are unique names that distinguish variables, functions, classes, modules, etc., identifying data and objects within a program.

Note: An object refers to anything that includes data and the behavior (methods) related to this data. In Python, everything is an object.

1. Starting Character Rule: An identifier must start with a letter (A-Z, a-z) or an underscore (_). It cannot start with a digit.

2. Use of Characters, Digits, Underscore: After the first character, it can be followed by letters, digits (0-9), or underscores (_).

3. Reserved Keywords Cannot Be Used: Keywords reserved for certain functionalities, like def, if, cannot be used as identifiers.

4. Case Sensitivity: Python identifiers are case-sensitive. myname and myName are considered different identifiers.

Copy
# Valid identifier examples
my_variable = 10    # Variable name starts with a letter or underscore

def my_function():  # Function name starts with a letter or underscore
    print("Hello")

class MyClass:      # Class name starts with a letter or underscore
    pass


# Invalid identifier examples
2my_variable = 10   # Variable name cannot start with a digit

def if():           # 'if' keyword cannot be used as a function name

Identifiers such as variable names, function names, and class names should be named to clearly reflect their role and purpose.

Copy
radius = 25  # Variable name representing the radius

def calculate_circle_area(radius): # Function name to calculate circle area
    return 3.14 * radius * radius

Try entering the highlighted 1_my_number = 7 on the practice screen.

You'll see an error occurs when a variable name starts with a digit.