Lesson 11: Module 3 Hands-on Projects

In this final lesson for Module 3, we will combine all our knowledge of functions and modularity to build a Custom Utility Library. This library will contain reusable tools for file management, math, and string manipulation.

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Project: Building the "PyBuddy" Utility Library

We will split our library into three files:

1. helpers.py: Contains our core logic functions.
2. constants.py: Stores our configuration and fixed values.
3. app.py: The user interface that imports and uses our library.

Part 1: constants.py

VERSION = "1.0.0"
AUTHOR = "Python Beginner"
TAX_RATE = 0.08

Part 2: helpers.py (The Logic)

import math

def format_title(text):
    """Capitalizes the first letter of every word."""
    return text.title()

def calculate_total(price, quantity=1, discount=0):
    """Calculates price with tax and optional discount."""
    subtotal = price * quantity
    subtotal -= (subtotal * (discount / 100))
    return subtotal * 1.08 # Uses our tax rate logic

def get_circle_info(radius):
    """Returns both area and circumference as a tuple."""
    area = math.pi * (radius ** 2)
    circ = 2 * math.pi * radius
    return (round(area, 2), round(circ, 2))

Part 3: app.py (The Execution)

import helpers
import constants

print(f"Welcome to PyBuddy v{constants.VERSION}")

# 1. Using String Helper
raw_name = "welcome to python programming"
print(f"Formatted: {helpers.format_title(raw_name)}")

# 2. Using Math Helper
area, circ = helpers.get_circle_info(5)
print(f"Radius 5: Area={area}, Circumference={circ}")

# 3. Using Sales Helper
total = helpers.calculate_total(100, quantity=2, discount=10)
print(f"Final Total: ${total}")

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Module 3 Recap: Exercises and Quiz

Exercise 1: The Scope Test

Predict the output of this code without running it:

x = 10
def change():
    x = 20
change()
print(x)

Exercise 2: Refactor Me

Break this long script into two clean functions: get_input() and process_data().

data = input("Enter numbers separated by space: ").split()
nums = [int(n) for n in data]
avg = sum(nums) / len(nums)
print(f"The average is {avg}")

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Module 3 Quiz

1. Which keyword is used to return data from a function? A) give B) exit C) return D) break

2. What happens to a local variable when the function ends? A) It becomes a global variable. B) It is deleted from memory. C) It remains accessible until the program ends. D) It is saved into a hidden file.

3. What is the correct way to import a specific function from a module? A) import function from module B) from module import function C) get function in module D) use module.function

4. True or False: Default parameters must come before positional parameters in a definition.

5. What is the main purpose of a docstring? A) To make the code run faster. B) To explain what the function does for other programmers. C) To encrypt the function logic.

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Quiz Answers

1. C | 2. B | 3. B | 4. False (They must come after!) | 5. B

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Conclusion

Congratulations on completing Module 3: Functions and Modular Programming! You no longer write simple scripts—you build systems.

Next up, we move into the single most important concept in modern programming: Module 4: Object-Oriented Programming (OOP). Get ready to think in Objects!