What are Python Identifiers?

A Python identifier is a name used to identify a variable, function, class, module or other object. An identifier starts with a letter A to Z or a to z or an underscore (_) followed by zero or more letters, underscores and digits (0 to 9).

Python does not allow punctuation characters such as @, $, and % within identifiers. Python is a case sensitive programming language. Thus, Manpower and manpower are two different identifiers in Python.

Rules for Python Identifiers

Python identifiers must follow these rules ?

• Must start with a letter (a-z, A-Z) or underscore (_)
• Can contain letters, digits (0-9), and underscores
• Cannot start with a digit
• Cannot contain spaces or special characters (@, $, %, etc.)
• Case sensitive (Age and age are different)
• Cannot be a Python keyword

Valid and Invalid Examples

Valid Identifiers

# Valid identifier examples
name = "John"
age_limit = 18
_private_var = 100
user123 = "Alice"
MyClass = "Example"

print(name, age_limit, _private_var, user123, MyClass)

John 18 100 Alice Example

Invalid Identifiers

# These will cause syntax errors
2name = "Invalid"        # Cannot start with digit
user-name = "Invalid"    # Hyphen not allowed
class = "Invalid"        # Python keyword
user@email = "Invalid"   # Special character not allowed

Naming Conventions

Python follows these naming conventions ?

• Variables and functions: Use lowercase with underscores (snake_case)
• Classes: Use CamelCase starting with uppercase
• Constants: Use ALL_UPPERCASE with underscores
• Private variables: Start with single underscore (_variable)
• Name mangling: Start with double underscore (__variable)
• Special methods: Surrounded by double underscores (__init__)

Examples of Naming Conventions

# Variables and functions (snake_case)
user_name = "Alice"
total_count = 50

def calculate_age():
    return 25

# Class names (CamelCase)
class StudentRecord:
    pass

# Constants (ALL_UPPERCASE)
MAX_SIZE = 100
PI_VALUE = 3.14159

print(f"User: {user_name}, Count: {total_count}")
print(f"Max size: {MAX_SIZE}")

User: Alice, Count: 50
Max size: 100

Reserved Keywords

Python has reserved keywords that cannot be used as identifiers ?

import keyword

# Display all Python keywords
keywords = keyword.kwlist
print(f"Total keywords: {len(keywords)}")
print("First 10 keywords:", keywords[:10])

Total keywords: 35
First 10 keywords: ['False', 'None', 'True', 'and', 'as', 'assert', 'break', 'class', 'continue', 'def']

Conclusion

Python identifiers must follow specific rules and naming conventions for clean, readable code. Use descriptive names, follow snake_case for variables and CamelCase for classes, and avoid reserved keywords.