Modules and Packages — PythonLessonLab

THE IDEA

Understand the concept

A module is a file of reusable Python code. import makes its names available through the module name, as in math.sqrt(). A package organizes related modules.

You can import a particular name with from ... import ..., or choose a short alias with as. For beginner code, keeping the module name visible often makes it easier to see where a function came from.

import a module
Use module.name
Packages group modules

WORKED EXAMPLES

See it step by step

Read the code, predict the output, then compare it with the result.

01. Use math functions

PYTHON

import math
print(math.sqrt(49))
print(math.ceil(2.2))

EXPECTED OUTPUT

7.0
3

The math module groups related functions. Use math.name to access a function after import.

02. Use a second module

PYTHON

import statistics
scores = [4, 8, 12]
print(statistics.mean(scores))

EXPECTED OUTPUT

statistics is another standard library module. mean() calculates the average of the three numbers.

HANDS-ON

Try it in Python

Edit the example and run it. Python starts in your browser the first time you click Run.

Python console

Ready to run

import math

radius = 3
area = math.pi * radius ** 2
print(f"Area: {area:.2f}")
print(math.sqrt(81))

Need input()? Add one value per line

Input lines

Ctrl / ⌘ + Enter to run

OUTPUT

Your output appears here.

Your turnImport the random module, store one random.randint(1, 6) result in roll, and print roll as a simulated die roll.

Need a hint?

Add import random near import math. Save the result with roll = random.randint(1, 6), then print(roll). Each run may show a different whole number.

Complete the task and select Check task to verify your code.

KNOWLEDGE CHECK

Quick quiz

Three questions. You can change your answers and try again.

DEBUG BETTER

Typical mistakes

Everyone meets these errors. See what causes them and how to fix them.

Using a module before importing it

COMMON MISTAKE

print(math.sqrt(9))

FIX

import math
print(math.sqrt(9))

What happens: NameError if math has not been imported in this run.
Import the module before using its name.

Shadowing the module name