• Module = a single Python file (.py).
• Package = a folder that contains multiple modules.
• Packages help organize big projects in a clean structure.
• Traditionally, package folder contains __init__.py (still commonly used).

project/
    main.py
    mypkg/
        __init__.py
        calc.py
        utils.py

• Create a folder (package) and add Python modules inside it.
• Add __init__.py file to mark it as a package (recommended).

def add(a, b):
    return a + b

from mypkg.calc import add

print(add(10, 20))

• import module
• import module as alias
• from module import name
• from module import * (not recommended)

import math
print(math.sqrt(25))

import math as m
print(m.pi)

from math import factorial
print(factorial(5))

• os → file/folder & OS tasks
• sys → system info, argv
• math → maths functions
• random → random values
• datetime → date/time
• json → JSON handling
• csv → CSV handling

import os
import datetime

print(os.getcwd())
print(datetime.datetime.now())

• Virtual environment keeps project dependencies separate.
• Prevents version conflicts between projects.
• Each project can have its own libraries and versions.

# Example
Project A uses Django 4
Project B uses Django 5
Virtual env keeps both separate

• Create virtual env using python -m venv.
• Activate it before installing packages.

python -m venv venv
venv\Scripts\activate

python3 -m venv venv
source venv/bin/activate

deactivate

• pip is Python package installer.
• Install packages after activating virtual environment.
• Use pip list to see installed packages.

pip install requests
pip install flask
pip list

• After installation, import and use the library.

import requests

res = requests.get("https://example.com")
print(res.status_code)
print(res.text[:100])

• requirements.txt stores all dependency versions.
• Useful to run same project on another system.

pip freeze > requirements.txt
pip install -r requirements.txt