Modules – ready-made toolboxes

What you'll learn

Import modules like math and random
Tell import, from … import and as apart
Write and use your own module

Don’t build everything yourself

Python comes with hundreds of ready-made modules – toolboxes for maths, randomness, time, files and much more. With import you bring one of them into your program:

import math

print(math.pi)
print(math.sqrt(81))
print(math.floor(3.9), math.ceil(3.1))

Three ways to import

import random                 # whole module: random.randint(...)
from math import sqrt         # just one function: sqrt(...)
import datetime as dt         # with a short name: dt.date.today()

print(random.randint(1, 6))
print(sqrt(16))
print(dt.date(2026, 12, 24).weekday())

Notation	Call afterwards
`import math`	`math.sqrt(9)`
`from math import sqrt`	`sqrt(9)`
`import math as m`	`m.sqrt(9)`

Randomness with random

random is perfect for games:

import random

dice = [random.randint(1, 6) for _ in range(5)]
print("Roll:", dice)
print("Winner:", random.choice(["Mia", "Ben", "Lea"]))

Your own module

A module is simply a .py file. Here we write one – and import it straight away:

with open("tools.py", "w") as file:
    file.write("def greeting(name):\n    return f'Hello {name}!'\n")

import tools
print(tools.greeting("Codelix"))

Remember: In the browser you get the modules of Python’s standard library. Extra packages like numpy would have to be installed separately.

Quick check

Before you start the task: what does this program print? Type your guess – then Python works it out.

import math
print(math.sqrt(16), math.floor(3.7))

Your task

Your turn

Import the function sqrt and the number pi from the module math. Write a function circle_area(r) that returns the area of a circle (π · r²), and a function diagonal(a, b) that uses Pythagoras' theorem to calculate the diagonal of a rectangle (√(a² + b²)).

# Import sqrt and pi from math here


def circle_area(r):
    pass


def diagonal(a, b):
    pass


print(round(circle_area(2), 2))
print(diagonal(3, 4))

Something to think about
Write from math import sqrt, pi at the very top.
Which command helps?
Area = pi * r ** 2 – and give it back with return.
Diagonal = sqrt(a ** 2 + b ** 2)

Gap code – fill in the ___

                        ___


def circle_area(r):
    return ___


def diagonal(a, b):
    return ___


print(round(circle_area(2), 2))
print(diagonal(3, 4))

Solve it without hints to earn a ⭐ on your progress page.

Show solution

Try it yourself first – mistakes teach you the most. Here is one possible solution:

from math import sqrt, pi


def circle_area(r):
    return pi * r ** 2


def diagonal(a, b):
    return sqrt(a ** 2 + b ** 2)


print(round(circle_area(2), 2))
print(diagonal(3, 4))