Modules, Packages & pip

A module is a Python file full of code you can reuse. You bring it into your program with import. Python comes with a huge standard library of ready-made modules:

import math          # bring in the math module

print(math.sqrt(16))    # 4.0
print(math.pi)          # 3.141592653589793

You can also install thousands of extra packages written by others using pip. Let's see how it all fits together.

Importing modules

There are a few import styles. Pick the one that reads best:

# Import the whole module, use module.name
import random
print(random.randint(1, 6))     # a dice roll: 1 to 6

# Import specific names directly
from math import sqrt, pi
print(sqrt(25))                  # 5.0  (no math. prefix needed)

# Give a module a shorter alias
import datetime as dt
print(dt.date.today())           # today's date

Useful standard library modules

The standard library ships with Python — no installation needed. A few you'll meet early:

import random
print(random.choice(["heads", "tails"]))   # random pick

import math
print(math.floor(3.7), math.ceil(3.2))      # 3 4

import datetime
now = datetime.datetime.now()
print(now.year)                              # current year

Writing your own module

Any .py file you write is a module you can import. Say you have a file helpers.py:

# helpers.py
def greet(name):
    return f"Hello, {name}!"

PI = 3.14159

In another file in the same folder, import and use it:

# main.py
import helpers

print(helpers.greet("Asha"))    # Hello, Asha!
print(helpers.PI)               # 3.14159

A package is just a folder of related modules. As programs grow, packages keep code organised.

Installing packages with pip

For tools outside the standard library — like requests for web requests — use pip, Python's package installer. Run these commands in your terminal, not inside a Python file:

# Install a package
pip install requests

# On Mac/Linux you may need pip3
pip3 install requests

# See what's installed
pip list

# Install a specific version
pip install requests==2.31.0

Then use it in your code:

import requests

response = requests.get("https://api.github.com")
print(response.status_code)     # 200 if it worked

Virtual environments (highly recommended)

A virtual environment keeps each project's packages separate, so projects don't clash. Create and activate one before installing packages:

# Create a virtual environment named .venv
python -m venv .venv

# Activate it
# On Windows:
.venv\Scripts\activate
# On Mac/Linux:
source .venv/bin/activate

# Now pip install affects only this project
pip install requests

When you're done, type deactivate. Using a virtual environment per project is a habit worth building early.

Common mistakes

• Running pip inside Python: pip install requests goes in the terminal, not in a .py file or the Python shell.
• ModuleNotFoundError: You tried to import something you haven't installed, or you installed it in a different environment. Check with pip list and your active virtual environment.
• Naming your file like a module: Saving a file as random.py or math.py shadows the real module and causes confusing errors. Avoid those names.
• pip vs pip3: On Mac/Linux, pip may point to an old Python. Use pip3, or better, python -m pip install ... to be sure you're using the right one.
• Forgetting to activate the virtual environment: If imports work in one terminal but not another, you probably forgot to activate the venv.

FAQ

What's the difference between a module and a package? A module is a single .py file. A package is a folder containing multiple modules (with the files organised together).

Where does pip download packages from? From the Python Package Index (PyPI) at pypi.org — a public repository of community and official packages.

Do I need a virtual environment for small scripts? Not strictly, but it's a great habit. It prevents version conflicts once you work on more than one project.

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Modules unlock powerful tools like the ones used in Regular Expressions in Python and Web Scraping Basics with Python. Build on your knowledge from Functions in Python too. More on the Python learning hub.

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