Chapter 4: Functions and Modules

Estimated time to read: 3 minutes

In this chapter, we will cover functions and modules, which allow you to write reusable code and organize your program into smaller, more manageable pieces.

4.1 Functions

Functions allow you to encapsulate a block of code into a single unit that can be called from anywhere in your program. Here's the basic syntax for defining a function:

def function_name(arguments):
    # code to be executed
    return value

For example, let's say we want to write a program that calculates the area of a circle. We can encapsulate the formula for calculating the area into a function:

import math

def area_of_circle(radius):
    area = math.pi * radius ** 2
    return area

In this example, we use the math module to access the value of pi, and then define a function that takes a radius as an argument, calculates the area of the circle using the formula pi * r^2, and returns the result.

To call the function, we simply pass a value for the radius:

radius = float(input("Enter the radius of the circle: "))
area = area_of_circle(radius)
print("The area of the circle is", area)

Mini-project 1:

Write a program that takes two numbers as input and calculates their average using a function.

Mini-project 2:

Write a program that takes a list of numbers as input and calculates their sum using a function.

4.2 Modules

Modules allow you to organize your code into separate files that can be imported and used in other programs. Here's an example:

# file: my_module.py

def greeting(name):
    print("Hello,", name)

In this example, we define a simple function that takes a name as an argument and prints out a greeting. To use this function in another program, we can import the module like this:

import my_module

my_module.greeting("Alice")

This will print out "Hello, Alice".

Mini-project 3:

Write a program that prompts the user to enter a number and checks if it's a prime number using a function defined in a separate module.

4.3 Function Arguments

Functions can take one or more arguments, which are values that are passed to the function when it's called. There are two types of arguments: positional arguments and keyword arguments.

4.3.1 Positional Arguments

Positional arguments are arguments that are passed to the function based on their position in the argument list. Here's an example:

def greet(first_name, last_name):
    print("Hello,", first_name, last_name)

In this example, we define a function that takes two positional arguments: first_name and last_name. To call this function, we simply pass values for these arguments in the correct order:

greet("Alice", "Smith")

This will print out "Hello, Alice Smith".

4.3.2 Keyword Arguments

Keyword arguments are arguments that are passed to the function using their names. Here's an example:

def greet(first_name, last_name):
    print("Hello,", first_name, last_name)

In this example, we define a function that takes two keyword arguments: first_name and last_name. To call this function, we pass values for these arguments using their names:

greet(last_name="Smith", first_name="Alice")

This will print out "Hello, Alice Smith".

Mini-project 1:

Write a program that takes a name as input and greets the person using a function that has a default value for the last name argument.

Mini-project 2:

Write a program that takes a list of names as input and calculates the length of each name using a function that takes a variable number of arguments.

4.4 Function Return Values

Functions can also return one or more values, which are values that are sent back to the caller when the function is finished executing. Here's an example:

def add_numbers(num1, num2):
    result = num1 + num2
    return result

In this example, we define a function that takes two numbers as arguments, adds them together, and returns the result. To use this function, we can assign the return value to a variable:

sum = add_numbers(3, 5)
print(sum)

This will print out "8".

Mini-project 3:

Write a program that takes a list of numbers as input and returns a new list containing only the even numbers using a function that uses a list comprehension.

Congratulations, you have completed the Functions and Modules chapter! With these skills, you can now write reusable code and organize your program into smaller, more manageable pieces.

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