python or py not found | Python not installed or not added to PATH (Windows) | Reinstall Python and check Add python.exe to PATH. Try py on Windows, python3 on macOS/Linux. |
| Can’t activate venv on Windows (script execution disabled) | PowerShell’s execution policy is blocking scripts | Open PowerShell as your user and run: Set-ExecutionPolicy -ExecutionPolicy RemoteSigned -Scope CurrentUser. Then try activating again. Only do this for your user account. |
ModuleNotFoundError: No module named 'flask' | Virtual environment not activated, or packages not installed | Activate your venv ((.venv)) and run pip install -r requirements.txt again. |
| Port 5000 already in use | Something else is running on port 5000 | Close the other program, or run Flask on a different port: flask run --port 5001. Remember to go to the new port in your browser. |
| Database errors | Corrupted or missing database | Delete instance/users.db and run python init_db.py again. |
| Page doesn’t load / connection refused | Server not running | Make sure the terminal with python app.py is still running and hasn’t crashed. Check for errors in that terminal. |
| Changes aren’t showing up | Browser cache or server not restarted | Hard refresh your browser (Ctrl+Shift+R or Cmd+Shift+R). If you changed app.py, restart the server with Ctrl+C and python app.py again. |
| Quotes being weird when copying payloads | Smart quotes from some documents | Always type the payloads exactly as shown in the book. Avoid copying from rich text documents, copy from the code blocks. |