mise-lang-python-overview

Python via mise

Python is the language where mise most often earns its keep — pyenv's compilation story is slow and fragile, and system Python is usually too old or too new. mise gives you per-project pinned Python without the pyenv tax.

Version resolution order

1. mise.toml [tools] python — explicit wins.
2. mise.local.toml override.
3. .tool-versions.
4. Idiomatic files, opt-in:

   [settings]
   idiomatic_version_file_enable_tools = ["python"]
   

   Reads .python-version and .python-versions (plural, pyenv's multi-version file).

The opt-in matters because a lot of Python projects leave stale .python-version files lying around, and silent promotion of those to authoritative would break migration from pyenv.

Pinning in mise.toml

[tools]
python = "3.12"          # major.minor — mise picks the latest patch
python = "3.12.7"        # exact
python = "3.12 3.11"     # multiple versions, first is default
python = "latest"        # avoid

For libraries: pin major.minor ("3.12"). Patch versions change often; don't churn your lockfile. For services in prod parity: pin exact ("3.12.7"). Match whatever prod runs.

Compile vs pre-built

By default, mise compiles Python from source using python-build (the same backend pyenv uses). This is slow (5-15 minutes depending on machine) but gives you:

• Matched libc/libssl on the host.
• Custom build flags if needed.
• Any Python version going back years.

Pre-built route (faster, fewer options):

export MISE_PYTHON_COMPILE=0    # use pre-compiled binaries when available
mise install python@3.12

Pre-built binaries come from astral-sh/python-build-standalone and only cover recent versions. Set this in your shell rc or project mise.toml:

[env]
MISE_PYTHON_COMPILE = "0"

Rule of thumb: use pre-built for dev speed. Use compiled for production-critical services where you need exact libc match.

Build dependencies (compile route)

If you're compiling Python, the host needs build tools:

Debian/Ubuntu:

sudo apt-get install -y build-essential libssl-dev zlib1g-dev libbz2-dev \
  libreadline-dev libsqlite3-dev curl libncursesw5-dev xz-utils tk-dev \
  libxml2-dev libxmlsec1-dev libffi-dev liblzma-dev

macOS (via Homebrew):

brew install openssl readline sqlite3 xz zlib tcl-tk libb2

Missing libs → Python compiles but modules silently don't work (import ssl fails, sqlite3 unavailable). The mise doctor command checks for these.

Virtual environments

mise pins the Python interpreter. It does not replace virtualenv / venv / uv / poetry — those manage the project's package set on top of a pinned interpreter.

The typical layout:

mise.toml         → python = "3.12"
pyproject.toml    → project deps (managed by uv/poetry/pip)
.venv/            → venv created by uv/poetry/python -m venv

mise can auto-activate a venv via:

[env]
_.python.venv = { path = ".venv", create = true }

This creates .venv using the mise-managed Python if it doesn't exist, and activates it whenever you cd into the project. Combined with uv/poetry, it's the cleanest Python setup available.

Common setups

Solo script / library

[tools]
python = "3.12"

[env]
MISE_PYTHON_COMPILE = "0"
_.python.venv = { path = ".venv", create = true }

[tasks.install]
run = "pip install -e '.[dev]'"
sources = ["pyproject.toml"]

uv-managed project

[tools]
python = "3.12"
"pipx:uv" = "latest"      # or cargo:uv if you prefer

[env]
MISE_PYTHON_COMPILE = "0"

[tasks.install]
run = "uv sync"
sources = ["pyproject.toml", "uv.lock"]

[tasks.test]
depends = ["install"]
run = "uv run pytest"

Data science (conda-ish without conda)

[tools]
python = "3.12"
"pipx:jupyterlab" = "latest"
"pipx:ruff" = "latest"

[env]
MISE_PYTHON_COMPILE = "0"
_.python.venv = { path = ".venv", create = true }

[tasks.lab]
run = "jupyter lab"

Auto-detection gotchas

1. .python-version from pyenv with system as the content — mise doesn't know what "system" means and errors. Delete the file or replace with a real version.
2. pyenv-virtualenv activation markers in .python-version (e.g. myvenv-3.12.7) — mise doesn't parse virtualenv names; use _.python.venv instead.
3. Compiling Python 2.7 or very old versions — python-build supports them but they're slow and missing security fixes. Don't.
4. Mixing mise Python with Homebrew Python on macOS — shims must be first on PATH. Check with which python.

See also

• mise-lang-python-packages — uv vs poetry vs pipx vs pip decision.
• mise-migrate-from-pyenv — moving off pyenv.
• mise-env-directives — _.python.venv and other auto-activate directives.
• mise docs: mise.jdx.dev/lang/python.html.
• python-build-standalone: github.com/astral-sh/python-build-standalone.