Functions and Modules

Functions

Functions are the building blocks of Python code. In a Django project you'll use functions for:

HTTP request handlers (function-based views)
Utility helpers (shared logic used across views, forms, tasks)
Template filters and simple template tags
Signal receivers and management command helpers

Why functions matter in Django

Functions keep code DRY and testable. Use small, single-responsibility functions in your views and move business logic to utilities so you can unit-test them without HTTP requests.

Basic function syntax

A simple Python function:


def add(a, b):
    """
    Add two numbers and return the result.
    """
    return a + b

Example: function-based view (simple)

A minimal function-based view that uses a helper function:


# views.py
from django.http import HttpResponse
from .utils import render_welcome_message

def welcome_view(request):
    message = render_welcome_message(request.user)
    return HttpResponse(message)

# utils.py
def render_welcome_message(user):
    if user.is_authenticated:
        return f"Welcome back, {user.username}!"
    return "Welcome, guest!"

Example: small utility function for tests

Extract logic into utilities to make testing easy:


# utils/strings.py
def slugify_title(title: str) -> str:
    """Return a URL-friendly slug for a blog title."""
    return "-".join(title.lower().split())

Decorator example (useful for views and utilities)

Decorators let you wrap functions with reusable behaviors, e.g., a simple execution timer for debugging:


import time
from functools import wraps

def timing(func):
    @wraps(func)
    def wrapper(*args, **kwargs):
        start = time.time()
        result = func(*args, **kwargs)
        elapsed = time.time() - start
        print(f"{func.__name__} took {elapsed:.3f}s")
        return result
    return wrapper

@timing
def expensive_calculation(n):
    # ...
    return n * n

Common pitfalls

Too much logic in views: move complex code to utilities or services
Mutable default args: avoid using mutable objects as default parameter values
Circular imports: place shared helpers in a separate module (e.g., utils) and import lazily if needed

Quick exercise

Create a helper function format_currency(amount, currency="NPR") that returns a formatted string like "NPR 1,234.00". Write a unit test for it.

Functions