What are Identifiers?

Identifiers are names used to label variables, functions, classes, modules, and other objects in 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: Words like def and if, which are reserved for specific language functions, cannot be used as identifiers.

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

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# 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 like variable, function, and class names should be descriptive and reflect their purpose in the code.

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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.