Virtual Environment
An isolated Python install letting each project use its own package versions.
- Tools: venv (built-in), conda, uv.
- One project = one venv.
- Solves "global package collision" pain.
When to use: Every new ML project to prevent dependency conflicts.
Example: python -m venv .venv && source .venv/bin/activate (or .venv\Scripts\activate on Windows).