Should I use "camel case" or underscores in Python?

CamelCase vs. Underscores: Python Naming Conventions Demystified

Explore Python's naming conventions, understand the differences between camel case and underscores, and learn when to apply each style for clean, readable, and PEP 8 compliant code.

Python, renowned for its readability, places a strong emphasis on consistent code style. A cornerstone of this consistency lies in naming conventions. New and even experienced Python developers often grapple with a fundamental question: should I use camelCase or snake_case (underscores) for my variables, functions, and classes? This article delves into Python's official style guide, PEP 8, to provide clarity on this matter, offering practical examples and best practices to write idiomatic Python code.

Understanding Python's Naming Philosophy (PEP 8)

PEP 8, the Python Enhancement Proposal that outlines the style guide for Python code, is the authoritative source for naming conventions. Its primary goal is to improve the readability and consistency of Python code, making it easier for multiple developers to collaborate and understand each other's work. While Python doesn't strictly enforce these rules, adhering to them is considered a best practice and a hallmark of a professional Python developer. The guide provides specific recommendations for different types of identifiers.

PEP 8 Naming Convention Decision Tree

Snake Case (snake_case): The Pythonic Standard

For most identifiers in Python – including variables, functions, and module names – PEP 8 strongly recommends snake_case. This convention involves using all lowercase letters, with words separated by underscores. The rationale behind this is that it enhances readability, especially for longer names, by visually separating words more clearly than camelCase does in many fonts and editors. It's a convention deeply ingrained in the Python community and ecosystem.

# Variables
first_name = "Alice"
total_items_in_cart = 15
is_user_active = True

# Functions
def calculate_total_price(item_cost, quantity):
    return item_cost * quantity

def get_user_data(user_id):
    # ... function logic
    pass

# Module name (example_module.py)
# def process_data():
#    pass

Examples of snake_case for variables and functions

Camel Case (CamelCase or CapWords): Reserved for Classes

While snake_case dominates, CamelCase (specifically CapWords, where each word starts with a capital letter without spaces or underscores) has a dedicated place in Python: class names. This distinction helps differentiate classes from functions and variables at a glance. It's a convention borrowed from other languages but specifically applied to class definitions in Python to maintain consistency within its object-oriented paradigm.

# Class Definitions
class UserProfile:
    def __init__(self, username, email):
        self.username = username
        self.email = email

class ShoppingCartManager:
    def __init__(self):
        self.items = []

# Incorrect usage (for illustration - avoid this for variables/functions)
def getCustomerDetails(): # This would be `get_customer_details`
    pass

myOrderProcessor = ShoppingCartManager() # This would be `my_order_processor`

Examples of CamelCase for class names and incorrect usage for other identifiers

Other Naming Conventions

Beyond snake_case and CamelCase, PEP 8 also provides guidelines for other specific scenarios:

• Constants: Use ALL_CAPS_WITH_UNDERSCORES. These are typically defined at the module level.
• Private/Internal Use: Prefix a single leading underscore (_variable_name) to indicate that a variable or method is intended for internal use within a module or class. This is a convention, not an enforcement mechanism.
• Name Clashes: Use a trailing underscore (class_) to avoid clashes with Python's built-in keywords.
• Dunder Methods: Double leading and trailing underscores (__init__, __str__) are reserved for special 'magic' methods and attributes in Python. Avoid creating your own names with this pattern unless you know what you're doing.

# Constants
MAX_CONNECTIONS = 100
DEFAULT_TIMEOUT_SECONDS = 30

# Internal Use
class MyClass:
    def __init__(self, value):
        self._internal_value = value # Intended for internal use

    def _private_method(self):
        print(self._internal_value)

# Avoiding keyword clashes
def func(class_):
    print(f"The class is {class_}")

# Dunder methods (typically not user-defined like this)
# class Example:
#    def __len__(self):
#        return 0

Examples of constants, internal variables, and keyword clash avoidance

Adhering to PEP 8's naming conventions might feel restrictive at first, but it quickly becomes second nature. The benefits of a consistent, readable codebase far outweigh the initial effort. By embracing snake_case for functions and variables and CamelCase for classes, you'll be writing Python code that is not only functional but also elegantly aligned with the language's core principles.