Lesson 17 of 21 · about 6 minutes with the exercises

Modules and import

Python comes with a large collection of ready-made code called the standard library. It is split into modules, each about one subject: maths, random numbers, dates, files and many more. A module is brought into your program with import. Learning to use modules means you stop writing things that already exist.

Importing a module

import math

print(math.sqrt(144))
print(math.pi)

Output

12.0
3.141592653589793

After import math, everything inside the module is reached with the module name and a dot. By custom, imports go at the very top of the file.

Other ways to import

from math import sqrt, pi
print(sqrt(81), pi)

import datetime as dt
print(dt.date(2026, 1, 26).year)

Output

9.0 3.141592653589793
2026

from module import name brings in just the names you list. You then use them without the prefix.
import module as short gives the module a shorter nickname.

Avoid from math import *, which brings in everything. It hides where each name came from and can quietly replace your own variables.

The math module

import math

print(math.sqrt(2))
print(math.floor(7.9), math.ceil(7.1))
print(math.gcd(48, 36))
print(math.factorial(5))
print(round(math.pi * 7 ** 2, 2))

Output

1.4142135623730951
7 8
12
120
153.94

Name	What it gives
`math.sqrt(x)`	square root
`math.floor(x)`	the whole number just below
`math.ceil(x)`	the whole number just above
`math.gcd(a, b)`	highest common factor
`math.factorial(n)`	n factorial
`math.pi`	the value of pi

ceil is handy for questions such as "how many buses for 130 children if a bus holds 40?".

import math
print(math.ceil(130 / 40), "buses")

Output

4 buses

The random module

random makes programs unpredictable: games, quizzes, picking a winner. The output below will differ every time you run it, so these examples first call random.seed(1). A seed makes the "random" choices repeat, which is useful for testing. Leave it out in real programs.

import random
random.seed(1)

print(random.randint(1, 6))
print(random.choice(["Asha", "Ravi", "Meena"]))
cards = [1, 2, 3, 4, 5]
random.shuffle(cards)
print(cards)
print(random.sample(range(1, 50), 3))

Output

2
Meena
[4, 2, 5, 3, 1]
[49, 29, 31]

Name	What it does
`random.randint(a, b)`	a whole number from a to b, both included
`random.choice(list)`	one item picked from a list
`random.shuffle(list)`	mixes the list in place
`random.sample(items, k)`	k different items
`random.random()`	a float from 0 up to, but not including, 1

Note that randint includes both ends, unlike range. One warning: this module is for games and simulations. For passwords and anything to do with security, Python has a separate module called secrets.

The datetime module

Dates are harder than they look, with months of different lengths and leap years. Let the module do the work.

import datetime

republic = datetime.date(2027, 1, 26)
today = datetime.date(2026, 11, 12)
print(republic - today)
print((republic - today).days, "days to go")
print(republic.strftime("%d %B %Y"))
print(republic.strftime("%A"))

Output

75 days, 0:00:00
75 days to go
26 January 2027
Tuesday

Subtracting two dates gives the gap between them. strftime turns a date into text using format codes.

Code	Meaning	Example
`%d`	day of the month	26
`%m`	month as a number	01
`%B`	month name	January
`%Y`	year	2027
`%A`	day of the week	Tuesday

The example above uses a fixed date so that its output stays the same. For the real current date, call datetime.date.today().

To move forwards or backwards in time, add a timedelta.

import datetime

start = datetime.date(2026, 11, 12)
due = start + datetime.timedelta(days=45)
print(due)
print(due.strftime("%d/%m/%Y"))

Output

2026-12-27
27/12/2026

Finding out what a module offers

Two built-in functions help you explore. dir(module) lists the names inside it. help(module.name) prints the explanation written by its authors. The complete reference is the official documentation at docs.python.org.

import math
names = [n for n in dir(math) if not n.startswith("_")]
print(len(names), "names, such as", names[:5])

Output

62 names, such as ['acos', 'acosh', 'asin', 'asinh', 'atan']

Modules beyond the standard library

Thousands of extra packages exist for web work, data and more. They are installed with a tool called pip. As a beginner you do not need any of them. Everything in these lessons uses only what comes with Python.

Do not name your file after a module

If you save your own program as random.py or math.py, then import random loads your file instead of the real module, and nothing works. Choose a different file name. This mistake produces a confusing AttributeError.

Try it yourself

Exercise 1. Use math to find the length of the long side of a right-angled triangle whose short sides are 5 and 12.

Show one answer

import math
print(math.sqrt(5 ** 2 + 12 ** 2))

Output

13.0

Exercise 2. Simulate rolling two dice and print both numbers and their total. Use random.seed(7) so the answer can be checked.

Show one answer

import random
random.seed(7)
a = random.randint(1, 6)
b = random.randint(1, 6)
print(a, b, a + b)

Output

3 2 5

Exercise 3. How many days are there between 15 August 1947 and 26 January 1950?

Show one answer

import datetime
gap = datetime.date(1950, 1, 26) - datetime.date(1947, 8, 15)
print(gap.days)

Output

Examples on this page were run with Python 3.14 on 12 November 2026. The output shown is the real output.

This is an independent learning site. It is not connected with or approved by the Python Software Foundation. "Python" is a trademark of the Python Software Foundation and is used here only to name the language.