Environment Management

uv manages Python versions as well as packages. When a command needs a Python you don't have, uv downloads it for you, so you don't need Python installed to get started. A project's virtual environment lives in a .venv folder inside the project, where editors can find it; keep it out of version control. Outside a project, uv venv --python <version> creates an environment with that version, and downloads it if needed.

virtualenv creates isolated Python environments, and a subset of it ships with Python as the venv module. Its docs place it between venv and uv: faster and more featureful than venv, and still pure Python. Pick it when you need plugins, or a Python API to create environments. It uses the Python it runs under unless you pass -p with another installed version. As a command-line tool, it belongs in an isolated environment, not your system Python.

pyenv does one job: it lets you switch between multiple versions of Python, and leaves virtual environments to you or its pyenv-virtualenv plugin. Install it with the automatic installer or, on macOS, Homebrew, then set up your shell for it. Choose the version with pyenv shell for the session, pyenv local for a directory, or pyenv global for your user account. Most versions are built from source as you install them, so install Python's build dependencies first. pyenv doesn't work on Windows outside the Windows Subsystem for Linux, so on Windows, use uv, which supports Windows.

mise installs tools such as Node.js, Python, and Go and selects their versions per project, so one tool covers Python and the rest of your stack. In a project, mise use python@<version> writes that version to a mise.toml file. Commit the file, and teammates and CI get the same tools with mise install. To also create and activate the project's virtual environment, add _.python.venv to the file's [env] section. Activate mise in your shell, and entering the project puts its Python on your PATH.

Whichever tools you combine, name each project's Python in a .python-version file. pyenv local writes that file, and so does uv python pin, whose docs recommend a plain version number there so other tools can read it. mise reads the file too, once you enable it for Python. virtualenv uses the version pyenv selected with no extra configuration. Don't install packages into the Python that came with your operating system, which often manages its packages itself; a virtual environment keeps yours apart.