Python

This page describes how Python is handled in Homebrew for users. See Python for Formula Authors for advice on writing formulae to install packages written in Python.

Homebrew should work with any CPython and defaults to the macOS system Python.

Homebrew provides formulae to brew Python 3.x.

Homebrew provided a python@2 formula until the end of 2019, at which point it was removed due to the Python 2 deprecation.

Important: If you choose to use a Python which isn’t either of these two (system Python or brewed Python), the Homebrew team cannot support any breakage that may occur.

Python 3.x

Homebrew provides a formula for Python 3.x ([email protected]).

The executables are organised as follows:

• python3 points to Homebrew’s Python 3.x (if installed)
• pip3 points to Homebrew’s Python 3.x’s pip (if installed)

Unversioned symlinks for python, python-config, pip etc. are installed here:

$(brew --prefix)/opt/python/libexec/bin

Setuptools, Pip, etc.

The Python formulae install pip (as pip3) and Setuptools.

Setuptools can be updated via pip3, without having to re-brew Python:

python3 -m pip install --upgrade setuptools

Similarly, pip3 can be used to upgrade itself via:

python3 -m pip install --upgrade pip

site-packages and the PYTHONPATH

The site-packages is a directory that contains Python modules (especially bindings installed by other formulae). Homebrew creates it here:

$(brew --prefix)/lib/pythonX.Y/site-packages

So, for Python 3.y.z, you’ll find it at /usr/local/lib/python3.y/site-packages.

Python 3.y also searches for modules in:

• /Library/Python/3.y/site-packages
• ~/Library/Python/3.y/lib/python/site-packages

Homebrew’s site-packages directory is first created if (1) any Homebrew formula with Python bindings are installed, or (2) upon brew install python.

Why here?

The reasoning for this location is to preserve your modules between (minor) upgrades or re-installations of Python. Additionally, Homebrew has a strict policy never to write stuff outside of the brew --prefix, so we don’t spam your system.

Homebrew-provided Python bindings

Some formulae provide Python bindings.

Warning! Python may crash (see Common Issues) if you import <module> from a brewed Python if you ran brew install <formula_with_python_bindings> against the system Python. If you decide to switch to the brewed Python, then reinstall all formulae with Python bindings (e.g. pyside, wxwidgets, pygtk, pygobject, opencv, vtk and boost-python).

Policy for non-brewed Python bindings

These should be installed via pip install <package>. To discover, you can use pip search or https://pypi.python.org/pypi.

Note: macOS’s system Python does not provide pip. Follow the pip documentation to install it for your system Python if you would like it.

Brewed Python modules

For brewed Python, modules installed with pip3 or python3 setup.py install will be installed to the $(brew --prefix)/lib/pythonX.Y/site-packages directory (explained above). Executable Python scripts will be in $(brew --prefix)/bin.

The system Python may not know which compiler flags to set in order to build bindings for software installed in Homebrew so you may need to run:

CFLAGS=-I$(brew --prefix)/include LDFLAGS=-L$(brew --prefix)/lib pip install <package>

Virtualenv

WARNING: When you brew install formulae that provide Python bindings, you should not be in an active virtual environment.

Activate the virtualenv after you’ve brewed, or brew in a fresh terminal window. Homebrew will still install Python modules into Homebrew’s site-packages and not into the virtual environment’s site-package.

Virtualenv has a --system-site-packages switch to allow “global” (i.e. Homebrew’s) site-packages to be accessible from within the virtualenv.

Why is Homebrew’s Python being installed as a dependency?

Formulae that declare an unconditional dependency on the "python" formula are bottled against Homebrew’s Python 3.x and require it to be installed.