pip
Python's standard package installer - fetches from PyPI and resolves dependencies.
- Ships with every modern Python.
- pip install -r requirements.txt; pip freeze.
- Use INSIDE an active venv to avoid system pollution.
When to use: Installing any Python library; pinning versions for reproducibility.
Example: pip install scikit-learn==1.4.1 installs a pinned version. pip install -e . is editable mode.