Python — PIP

The package installer

The standard library is huge, but PyPI hosts 500,000+ community packages:

pip install requests

That's it — the package downloads and becomes importable:

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

Everyday commands

pip install requests          # install latest
pip install "requests==2.31"  # exact version
pip install --upgrade requests
pip uninstall requests
pip list                      # what's installed
pip show requests             # version, location, dependencies

requirements.txt — reproducible projects

Freeze exactly what your project needs:

pip freeze > requirements.txt      # snapshot current environment

# requirements.txt
requests==2.31.0
pandas==2.2.0
flask>=3.0

Anyone (including future-you) rebuilds it:

pip install -r requirements.txt

Virtual environments — non-negotiable hygiene

Global installs eventually collide: project A needs pandas 1.x, project B needs 2.x. Virtual envs give each project its own isolated set:

python -m venv .venv              # create

# activate:
.venv\Scripts\activate            # Windows PowerShell
source .venv/bin/activate         # mac/linux

pip install requests              # installs ONLY inside .venv
deactivate                        # exit when done

Your prompt shows (.venv) while active. Delete the folder to reset completely.

Rule: never pip install into the system Python. One venv per project, always.

Popular first packages

Package	Superpower
requests	humane HTTP calls
pandas	data tables & analysis
flask / fastapi	web servers
pillow	image processing
pytest	testing

Finding good packages

1. Search pypi.org
2. Check: recent release date · download counts · docs quality
3. Prefer well-maintained over clever-and-abandoned

Troubleshooting quick hits

• 'pip' is not recognized → use python -m pip install …
• Permission errors → you're outside a venv; make one
• Slow builds → some packages compile C; wheels usually prebuilt on common platforms

Mini Practice

1. Create + activate a venv; confirm prompt change.
2. Install requests; verify with pip show.
3. Freeze requirements.txt; delete and reinstall from it.
4. Deactivate; prove the package vanished from global scope.
5. Install one new-to-you package and print its version in Python.

Next: try/except →