Key Takeaways — Chapter 2: Setting Up Your Python Environment
The Four Components You Installed
| Component | What It Is | How You Use It |
|---|---|---|
| Python | The interpreter that runs your code | python script.py |
| pip | The package installer | pip install pandas |
| Virtual environment | An isolated Python installation per project | python -m venv venv + activate |
| VS Code | Your code editor | Write and run code here |
The 4-Step Setup Habit
For every new Python project:
1. Create a folder
2. python -m venv venv — create the environment
3. Activate it (Windows: venv\Scripts\activate / macOS: source venv/bin/activate)
4. pip install your packages
Every time you return to a project:
1. Open VS Code in the project folder
2. Confirm the venv is active (look for (venv) in terminal)
3. Code
Command Quick Reference
python --version # Check Python version
python -m venv venv # Create virtual environment
source venv/bin/activate # Activate (macOS/Linux)
venv\Scripts\activate # Activate (Windows)
deactivate # Deactivate
pip install package # Install a package
pip freeze > requirements.txt # Save package list
pip install -r requirements.txt # Install from list
python script.py # Run a script
python # Enter REPL
jupyter notebook # Launch Jupyter
Three Ways to Run Python
| Method | Best For |
|---|---|
REPL (python) |
Quick tests, one-line calculations, exploration |
Script (python file.py) |
Automation, repeatable tasks, production code |
| Jupyter Notebook | Data exploration, charts, presenting findings |
Common Mistakes and Their Fixes
| Mistake | Fix |
|---|---|
| "python not recognized" | Add Python to PATH (reinstall, check the box) |
ImportError: No module named 'pandas' |
Activate your venv first; then install |
| Wrong Python version | where python (Win) / which python (Mac) to see what's being used |
| PowerShell script blocked | Set-ExecutionPolicy RemoteSigned |
The Golden Rule
Always activate your virtual environment before working on a project.
If you see (venv) at the start of your terminal prompt, you're in. If you don't see it, type the activate command.
Next: Chapter 3 teaches you the building blocks of Python — variables, data types, and operators — in the context of real business data.