Python · Quick Reference

Lesson 15 — Modules & Packages Cheat Sheet

Python

In one line: A module is simply a Python file. Any .py file can be imported by other files. When you write import math, Python finds math.py (or a compiled equivalent) and executes it, makin...

Key Ideas

1Creating & Importing Modules. A module is simply a Python file. Any .py file can be imported by other files. When you write import math, Python finds math.py (or a compiled equivalent) and executes...

2Packages — Organising Multiple Modules. A package is a folder containing an __init__.py file and multiple modules. This lets you organise large projects into namespaced sub-modules. The __init__.py runs when...

3pip & Virtual Environments. pip is Python's package installer. It downloads and installs packages from PyPI (Python Package Index). A virtual environment is an isolated Python installation for ea...

4Standard Library — Must-Know Modules. Python ships with an enormous standard library — "batteries included." These are the modules every Python developer reaches for regularly:

Code Examples

# mathutils.py — a reusable math utilities module

PI = 3.14159265358979

def circle_area(r):
    """Return area of a circle."""
    return PI * r ** 2

def circle_circumference(r):
    return 2 * PI * r

def is_prime(n):
    """Return True if n is prime.""...

# Style 1: import the whole module (namespace preserved)
import mathutils
print(mathutils.circle_area(3))   # 28.274...
print(mathutils.PI)                # 3.14159...

# Style 2: import specific names
from mathutils import is_prime, PI
print(is_prime(13)) ...

# __init__.py — package initialisation
# Import key names so users can write: from bwb_toolkit import validate_email
from .validators import validate_email, validate_age
from .formatters import format_currency, format_date

__version__ = "1.0.0"
__author__ ...