Organizing Functions in Files
When your programs grow beyond a few dozen lines, keeping everything in one file becomes unwieldy. Organizing functions into separate files makes your code easier to navigate, maintain, and reuse.
Why Organization Matters
Small programs work fine in a single file. But as you add more functions, finding what you need becomes harder. Grouping related functions together — all your math helpers in one place, all your formatting functions in another — creates a logical structure that helps you and others understand your code.
Think of it like organizing a kitchen. You don't throw all utensils, spices, and dishes into one drawer. You group related items together so you can find them quickly.
Files as Modules
In Python, each file is called a module. When you create a file called helpers.py, you've created a module named helpers. Other files can import functions from this module and use them.
# helpers.py
def calculate_tax(amount, rate):
return amount * rate
def format_currency(amount):
return f"${amount:.2f}"
Now your main program can import and use these functions:
# main.py
from helpers import calculate_tax, format_currency
total = 100
tax = calculate_tax(total, 0.08)
print(format_currency(total + tax)) # Output: $108.00
The from helpers import statement tells Python to look in helpers.py and bring in the specified functions.
Main Code vs Helper Functions
A common pattern separates your main logic from helper functions. Your main file orchestrates the program — handling user input, calling functions, and producing output. Helper files contain reusable functions that do specific tasks.
# string_utils.py - reusable string helpers
def clean_input(text):
return text.strip().lower()
def truncate(text, length):
if len(text) > length:
return text[:length] + "..."
return text
This separation means you can reuse string_utils.py in other projects without copying code.
Import Variations
Python offers several ways to import:
# Import specific functions
from helpers import calculate_tax
# Import everything (use sparingly)
from helpers import *
# Import the module itself
import helpers
helpers.calculate_tax(100, 0.08)
The first approach is usually clearest — you can see exactly which functions you're using.
When to Split Files
Start with one file. When you notice groups of related functions, or when scrolling becomes tedious, split them out. There's no magic number — use your judgment about what makes the code clearer.