Python pip Tutorial - Install Packages, Virtual Environment

What is PIP?

PIP (Pip Installs Packages) is Python's package manager. It lets you install, update, and remove third-party libraries from PyPI (Python Package Index) - a repository of over 500,000 packages.

Basic PIP Commands

PIP Commands

# Check pip version
pip --version
pip3 --version

# Install a package
pip install requests
pip install numpy
pip install "flask==3.0.0"       # specific version
pip install "django>=4.0,<5.0"   # version range

# Install multiple packages
pip install requests flask numpy

# Upgrade a package
pip install --upgrade requests

# Uninstall a package
pip uninstall requests

# List installed packages
pip list

# Show package info
pip show requests

# Search for packages (deprecated in newer pip, use pypi.org)
pip search flask

requirements.txt

A requirements.txt file lists all project dependencies. This is the standard way to share and reproduce project environments.

requirements.txt

# Generate requirements.txt from current environment
pip freeze > requirements.txt

# Install all packages from requirements.txt
pip install -r requirements.txt

# Install with exact versions (reproducible)
pip install -r requirements.txt --no-deps

# requirements.txt example
requests==2.31.0
flask==3.0.0
numpy>=1.24.0
pandas>=2.0.0,<3.0.0
python-dotenv
pytest>=7.0

Virtual Environments

A virtual environment is an isolated Python environment for each project. This prevents package version conflicts between projects.

Virtual Environments

# Create a virtual environment
python -m venv venv

# Activate (Windows)
venv\Scripts\activate

# Activate (macOS/Linux)
source venv/bin/activate

# Your prompt changes to: (venv) $

# Now install packages - they go into venv only
pip install requests flask

# Deactivate when done
deactivate

# Delete the environment (just delete the folder)
rm -rf venv

Best Practice: Always create a virtual environment for each project. Add venv/ to your .gitignore.

Popular Python Packages

Package	Category	Description
`requests`	HTTP	Simple HTTP requests
`flask`	Web	Lightweight web framework
`django`	Web	Full-featured web framework
`fastapi`	Web/API	Modern async API framework
`numpy`	Data Science	Numerical computing
`pandas`	Data Science	Data analysis and manipulation
`matplotlib`	Data Science	Data visualization
`scikit-learn`	ML	Machine learning algorithms
`tensorflow`	ML/AI	Deep learning framework
`pytest`	Testing	Testing framework
`sqlalchemy`	Database	SQL toolkit and ORM
`pillow`	Images	Image processing
`beautifulsoup4`	Web Scraping	HTML/XML parsing
`python-dotenv`	Config	Load .env files

Using requests

import requests

# GET request
response = requests.get("https://api.github.com/users/python")
print(response.status_code)   # 200
data = response.json()
print(data["name"])            # Python

# POST request
payload = {"username": "alice", "password": "secret"}
response = requests.post("https://httpbin.org/post", json=payload)
print(response.json())

# With headers and timeout
headers = {"Authorization": "Bearer TOKEN"}
response = requests.get(
    "https://api.example.com/data",
    headers=headers,
    timeout=10
)

# Error handling
try:
    response = requests.get("https://example.com", timeout=5)
    response.raise_for_status()   # raises for 4xx/5xx
    print(response.text)
except requests.exceptions.Timeout:
    print("Request timed out")
except requests.exceptions.HTTPError as e:
    print(f"HTTP error: {e}")