7.1 Module basics

Learning objectives

By the end of this section you should be able to

Write a module that consists only of function definitions.
Import the module and use the functions in a program.

Defining a module

Modules are defined by putting code in a .py file. The area module below is in a file named area.py. This module provides functions for calculating area.

Example 1 The area module

"""Functions to calculate the area of geometric shapes."""

import math

# 2D shapes

def square(side):
    """Gets the area of a square."""
    return side**2

def rectangle(length, width):
    """Gets the area of a rectangle."""
    return length * width

def triangle(base, height):
    """Gets the area of a triangle."""
    return 0.5 * base * height

def trapezoid(base1, base2, height):
    """Gets the area of a trapezoid."""
    return 0.5 * (base1 + base2) * height

def circle(radius):
    """Gets the area of a circle."""
    return math.pi * radius**2

def ellipse(major, minor):
    """Gets the area of an ellipse."""
    return math.pi * major * minor

# 3D shapes

def cube(side):
    """Gets the surface area of a cube."""
    return 6 * side**2

def cylinder(radius, height):
    """Gets the surface area of a cylinder."""
    return 2 * math.pi * radius * (radius + height)

def cone(radius, height):
    """Gets the surface area of a cone."""
    return math.pi * radius * (radius + math.hypot(height, radius))

def sphere(radius):
    """Gets the surface area of a sphere."""
    return 4 * math.pi * radius**2

Importing a module

The module defined in area.py can be used in other programs. When importing the area module, the suffix.py is removed:


    import area
    
    print("Area of a basketball court:", area.rectangle(94, 50))
    print("Area of a circus ring:", area.circle(21))

The output is:


    Area of a basketball court: 4700
    Area of a circus ring: 1385.4423602330987

Try It

Conversion module

Write a module that defines the following functions:

cel2fah(c) –
Converts a temperature in Celsius to Fahrenheit.
The formula is 9/5 * c + 32.
fah2cel(f) –
Converts a temperature in Fahrenheit to Celsius.
The formula is 5/9 * (f - 32).
km2mi(km) –
Converts a distance in kilometers to miles.
The formula is km / 1.60934.
mi2km(mi) –
Converts a distance in miles to kilometers.
The formula is mi * 1.60934.

Each function should include a docstring as the first line. A docstring for the module has been provided for you.

The module should not do anything except define functions. When you click the "Run" button, the module should run without error. No output should be displayed.

"""Functions that convert metric and imperial units."""

Try It

European vacation

Write a program that uses the conversion module from the previous exercise to complete a short story. The program's output should match the following example (input in bold):


    How fast were you driving? 180
    Woah, that's like 112 mph!
    What was the temperature? 35
    That's 95 degrees Fahrenheit!

Notice this exercise requires two files:

european.py, the main program. Input and output statements are provided as a starting point. Edit the lines with TODO comments to use the conversion module.
conversion.py, the other module. Copy and paste your code from the previous exercise. Import this module in european.py after the docstring.

"""Example program that uses the conversion module."""

speed_in_km = float(input("How fast were you driving? "))
speed_in_mi = 0  # TODO
print("Woah, that's like", round(speed_in_mi), "mph!")

temp_in_c = float(input("What was the temperature? "))
temp_in_h = 0  # TODO
print("That's", round(temp_in_h), "degrees Fahrenheit!")

Adapted from Introduction to Python Programming by OpenStax (openstax.org), licensed under CC BY-NC-SA 4.0. Changes were made. License: CC-BY-NC-SA-4.0.