Modules and the import statement

Python ships with hundreds of ready-made tools, and almost none of them are loaded until you ask. A module is a file of Python code, and the standard library is the collection of modules that comes with every Python installation. This lesson shows how to ask for one, how to find out what is inside, and how to use the two you will meet first: math and random.

You have already seen import math in the numbers lesson. Now you will see what that line does.

import

import math loads the module and gives you one new name, math. Everything inside the module is reached with a dot.

import math

print(math.sqrt(16))
print(math.floor(2.7), math.ceil(2.1))
print(round(math.pi, 4))

4.0
2 3
3.1416

math.sqrt means “the name sqrt inside math”. floor rounds down, ceil rounds up, and pi is a number, not a function, so it has no brackets. The dotted names tell the reader where each tool comes from, which is useful in a long program.

from … import and as

If you use a few names often, from brings them in directly, so you write sqrt rather than math.sqrt. The word as gives a module or a name a different, usually shorter, label.

from math import sqrt, pi
import statistics as stats

print(sqrt(25))
print(round(pi * 2**2, 2))
print(stats.mean([2, 4, 9]))

5.0
12.57
5

After from math import sqrt, pi, the names sqrt and pi exist on their own, but math does not. After import statistics as stats, the module is called stats, and statistics is not defined. Use from for a small number of names that are clear without their module. Use plain import when the module name adds meaning.

Avoid from math import *. It dumps every name into your file, hides where each one came from, and can silently replace names you defined earlier.

Finding out what is inside

Nobody remembers every module. Python can describe its own. dir(module) lists the names inside a module, and help(module.name) prints the documentation. In the REPL, help(math.hypot) opens the full text. In a script, the same text is available as __doc__.

import math

print("hypot" in dir(math))
print(math.hypot.__doc__.splitlines()[0])
print(type(math))

True
Multidimensional Euclidean distance from the origin to a point.
<class 'module'>

A module is a value like any other: type(math) is module. The first line of a docstring is a one-line summary, so help is the quickest way to learn what an unfamiliar function does. The documentation at docs.python.org/3/library/ describes every module.

random

The random module makes unpredictable numbers, which is what games and simulations need. Its output changes every run, so the example below prints True for each check instead of the random value.

import random

roll = random.randint(1, 6)
print(1 <= roll <= 6)

colour = random.choice(["red", "green", "blue"])
print(colour in ["red", "green", "blue"])

cards = [1, 2, 3, 4, 5]
random.shuffle(cards)
print(sorted(cards))

picked = random.sample(range(1, 50), 6)
print(len(picked), len(set(picked)))

random.seed(5)
first = [random.randint(1, 6) for _ in range(5)]
random.seed(5)
second = [random.randint(1, 6) for _ in range(5)]
print(first == second)

True
True
[1, 2, 3, 4, 5]
6 6
True

• randint(1, 6) includes both ends, unlike range. It is a dice roll.
• choice picks one item from a sequence.
• shuffle mixes a list in place and returns None, so write random.shuffle(cards), not cards = random.shuffle(cards).
• sample picks several different items, here six distinct numbers for a lottery ticket.
• seed(5) fixes the starting point of the sequence. The same seed gives the same “random” numbers every time, which is why first == second is True. Seeds are useful for repeatable tests and for exercises like the ones below.

The numbers from random are fine for games. They are not secure, so never use them to make passwords. The secrets module is for that.

A short tour of two more modules

Two more modules are worth knowing about now. You do not need to master them yet.

import statistics
from datetime import date

marks = [70, 85, 90, 85, 60]
print(statistics.mean(marks), statistics.median(marks))

release = date(2026, 10, 9)
print(release.strftime("%A"))
print((date(2026, 12, 25) - release).days)

78 85
Friday
77

statistics gives the average and the middle value of a list. datetime provides dates: you can ask for the weekday name, and subtracting two dates gives a duration whose .days is a number. Python 3.15 itself was released on Friday 9 October 2026, which is the date used above.

Do not name your file after a module

When you write import random, Python looks in the folder of your running script before it looks at the standard library. If you have a file called random.py next to your script, Python finds your file instead.

import random

print(random.randint(1, 6))

With a file called random.py in the same folder, this fails:

Traceback (most recent call last):
  File "/home/you/project/game.py", line 3, in <module>
    print(random.randint(1, 6))
          ^^^^^^^^^^^^^^
AttributeError: module 'random' has no attribute 'randint' (consider renaming '/home/you/project/random.py' since it has the same name as the standard library module named 'random' and prevents importing that standard library module)

The message reads strangely, because the module is real, just not the one you wanted. The fix is to rename your file. Avoid random.py, math.py, statistics.py, datetime.py and test.py.

The intermediate level covers writing your own modules, packages and how Python searches for them. For now, one file per program is enough.

Common pitfalls

• Forgetting the module name. After import math, writing sqrt(16) raises NameError. Write math.sqrt(16).
• Using the module name after from. After from math import pi, math.sqrt fails because math was never defined.
• from module import *. It hides where names come from and can overwrite yours.
• Reusing a standard name for a variable. random = 7 after import random replaces the module with a number. Name the variable roll.
• Expecting randint to exclude the top end. randint(1, 6) can return 6.
• Writing cards = random.shuffle(cards). It sets cards to None.

19.63
5.0
20

import math

radius = 2.5
area = math.pi * radius**2
print(round(area, 2))
print(math.hypot(3, 4))
print(math.ceil(area))

19.63
5.0
20

Days: 84
Weeks and days: 12 0

from datetime import date

start = date(2026, 10, 9)
end = date(2027, 1, 1)
days = (end - start).days
print("Days:", days)
print("Weeks and days:", days // 7, days % 7)

Days: 84
Weeks and days: 12 0

import random

roll = randint(1, 6)
print(1 <= roll <= 6)

import random

roll = random.randint(1, 6)
print(1 <= roll <= 6)

from random import randint

roll = randint(1, 6)
print(1 <= roll <= 6)

Summary

• import module gives you the module, used as module.name. from module import name brings in just the name. as renames either.
• dir(module) lists what is inside, and help(module.name) or its __doc__ explains it.
• math has sqrt, floor, ceil, pi and more. random has randint (both ends included), choice, shuffle, sample and seed.
• Never name your own file after a standard library module, because Python will find yours first.

Next: reading and writing files.