Organizing code

Why organize your code?

As your scripts grow, they become harder to read and maintain. The solution? Split your code into functions and separate files. Benefits:

Reusable - Write once, use many times
Readable - Main script stays simple and clear
Testable - Easy to test individual functions

Creating helper functions

Let’s create simple helper functions for our sales analysis. In your sales-analysis folder, create a new file called helpers.py:

# helpers.py

def calculate_total(quantity, price):
    """Calculate total for a single item"""
    return quantity * price

def format_currency(amount):
    """Format number as currency"""
    return f"${amount:,.2f}"

The :.2f in the format string rounds floating point numbers to 2 decimal places - perfect for displaying money!

That’s it! Two simple functions that do one thing each.

Using your functions

Now update analyzer.py to use these helpers:

# analyzer.py
import pandas as pd
from helpers import calculate_total, format_currency

# Read data
df = pd.read_csv('data/sales.csv')

# Calculate total for each row
totals = []
for index, row in df.iterrows():
    total = calculate_total(row['quantity'], row['price'])
    totals.append(total)

# Add totals to our data
df['total'] = totals

# Display with formatted totals
print("Sales Data:")
for index, row in df.iterrows():
    formatted_total = format_currency(row['total'])
    print(f"{row['product']}: {formatted_total}")

# Show grand total
grand_total = df['total'].sum()
formatted_grand_total = format_currency(grand_total)
print(f"\nGrand Total: {formatted_grand_total}")

How imports work

When you write from helpers import calculate_total:

Python looks for helpers.py in the same folder
It runs that file and makes the functions available
You can now use calculate_total() directly

The file must be in the same folder for this simple import to work. We covered more complex imports in the Python paths section.

What you’ve accomplished

Look at what you’ve built! You started with a single Python file and now have:

An organized project structure
Understanding of how Python finds files
Code that reads real data and saves results
Reusable functions in separate files

This is how real Python projects work. You’re ready to build bigger things!

Learn error handling

Handle errors gracefully in your code

Functions

External tools

Practical Python

Error handling

Classes

Why organize your code?

Creating helper functions

Using your functions

How imports work

What you’ve accomplished

Learn error handling

​Why organize your code?

​Creating helper functions

​Using your functions

​How imports work

​What you’ve accomplished

Learn error handling

Why organize your code?

Creating helper functions

Using your functions

How imports work

What you’ve accomplished