Modules & Packages

A module is just a .py file — anything you define in it (functions, classes, variables) can be imported elsewhere. A package is a folder of modules with an __init__.py file marking it as importable.

# math_utils.py
def add(a, b):
    return a + b

PI = 3.14159

# main.py
import math_utils
print(math_utils.add(2, 3))
print(math_utils.PI)

from math_utils import add        # import a specific name directly
print(add(2, 3))

import math_utils as mu           # alias, common for long/library names
print(mu.add(2, 3))

The Python standard library

Python ships with a large "batteries included" standard library — you don't install anything to use these:

import math
print(math.sqrt(16), math.pi)

import random
print(random.randint(1, 100))       # random int, inclusive both ends
print(random.choice(["Intro", "Loops", "Functions"]))

from datetime import date
print(date.today())

Third-party packages with pip

For anything beyond the standard library — like requests for HTTP calls, or numpy for numerical arrays — you install with pip, Python's package manager, from the terminal (not inside your script):

pip install requests

import requests
response = requests.get("https://api.github.com")
print(response.status_code)

It's standard practice to install packages inside a virtual environment (python -m venv venv) per project, so different projects' dependencies don't collide with each other on your system.

if __name__ == "__main__":

This guard lets a file work both as a standalone script and as an importable module — code inside it only runs when the file is executed directly, not when it's imported elsewhere.

def main():
    print("Running as a script")

if __name__ == "__main__":
    main()