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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

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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.

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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}")

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How imports work

When you write from helpers import calculate_total:
  1. Python looks for helpers.py in the same folder
  2. It runs that file and makes the functions available
  3. 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.

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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