Modules and import

Splitting code across files and unlocking Python’s enormous standard library — the key to writing bigger, cleaner programs.

"Python comes with batteries included. Before you write any code, check if Python’s standard library already solved the problem for you."

— ShurAI

What is a Module?

A module is simply a .py file containing Python code — functions, variables, and classes. When you import it, you get access to everything inside. Python ships with over 200 built-in modules in its standard library, ready to use the moment you install Python — no extra downloading needed.

Three Ways to Import

python

# 1. Import the whole module — use dot notation to access things
import math
print(math.sqrt(16))        # 4.0
print(math.pi)               # 3.141592...

# 2. Import specific names — call them directly, no dot needed
from math import sqrt, pi
print(sqrt(25))              # 5.0
print(pi)                    # 3.141592...

# 3. Import with an alias — shorter name to type
import datetime as dt
print(dt.date.today())       # today’s date

Which style to use?

Use import math when you need several things from a module — the dot shows clearly where each function came from. Use from math import sqrt for one or two functions you call constantly. Avoid from math import * — it dumps everything into your namespace and makes bugs hard to trace.

Exploring Any Module

python

import math

# List everything a module contains
print(dir(math))
# [’acos’, ’acosh’, ... ’sqrt’, ’tan’, ’tau’, ’trunc’]

# Read the built-in documentation for any function
help(math.sqrt)
# sqrt(x, /)  Return the square root of x.

Writing Your Own Module

Any .py file you create is a module. Save the file, then import it from another file in the same folder:

python — greetings.py

# greetings.py — your own module
SITE_NAME = "ShurAI"

def hello(name):
    return f"Hello, {name}! Welcome to {SITE_NAME}."

def goodbye(name):
    return f"See you soon, {name}!"

python — main.py

import greetings

print(greetings.hello("Riya"))    # Hello, Riya! Welcome to ShurAI.
print(greetings.goodbye("Riya"))  # See you soon, Riya!
print(greetings.SITE_NAME)         # ShurAI

The Standard Library — Your Free Toolkit

These are some of the most useful modules that come built into every Python installation:

math

Maths functions & constants

random

Random numbers & choices

os

Files, folders, system

datetime

Dates & times

json

Read & write JSON data

sys

Interpreter & exit

"The standard library is Python’s superpower. Every module was written by experts, tested by millions, and costs you nothing to use."

— ShurAI

🧠 Quiz — Q1

What does import math do?

🧠 Quiz — Q2

What is the difference between import math and from math import sqrt?

🧠 Quiz — Q3

What does dir(math) show you?

🧠 Quiz — Q4

You create utils.py with a function add(). How do you use it in another file in the same folder?