Modules and Libraries | AI Pathshala

Definition

Why rewrite what someone has already written and tested?

A module is a Python file of functions and values that other programs can import. A library or package is a collection of modules. Python's standard library comes built in, with modules such as math, random and datetime; third-party packages such as NumPy are installed with pip.

In simple words

import math gives you a toolbox: math.sqrt(16) is 4.0 and math.pi is 3.14159…. import random lets you roll dice. You can import just one tool, from math import sqrt, or give a module a short name, import numpy as np. On your own computer, pip install numpy downloads a package.

Why it matters

Nobody builds AI from nothing. Libraries such as NumPy, pandas, scikit-learn and PyTorch hold years of expert work. Knowing how to import and read a library's documentation is a core skill.

How it works

Module	Useful for	Example
math	Square roots, powers, pi, rounding	math.sqrt(81)
random	Random choices and numbers	random.choice(names)
datetime	Dates and times	date(2026, 1, 26)
statistics	Mean, median, mode	statistics.median(xs)
collections	Counter, deque and more	Counter(words)

In code

Four standard modules in action. The seed makes the random rolls the same every time.

modules.py

import math
import random
from datetime import date
from statistics import mean, median

print("Square root of 81:", math.sqrt(81))
print("Pi to 3 places:", round(math.pi, 3))

random.seed(42)
rolls = [random.randint(1, 6) for _ in range(5)]
print("Five dice rolls:", rolls)

day = date(2026, 1, 26)
print(day, "is a", day.strftime("%A"))

scores = [72, 91, 64, 85, 78]
print("Mean:", mean(scores), "Median:", median(scores))

Output

Square root of 81: 9.0
Pi to 3 places: 3.142
Five dice rolls: [6, 1, 1, 6, 3]
2026-01-26 is a Monday
Mean: 78 Median: 78

Try it yourself

Which module would you import?

Match each task to the standard module that helps.

Find the square root of 50
Pick a random winner from a list
Work out how many days until a festival
Find the median of some marks
Count how often each word appears

Common mistakes

Naming your own file math.py or random.py, which hides the real module.
Forgetting the module name: sqrt(16) fails after import math; use math.sqrt(16).
Installing packages inside a program. Run pip in the terminal, once.

Check yourself

1. After import math, how do you get the square root of 9?

2. What does random.seed(42) do?

3. How is a third-party package installed?

Summary

Modules are reusable Python files; packages group modules.
The standard library is built in; pip installs others.
import, from … import and import … as are the three forms.