pex is a library for generating .pex (Python EXecutable) files which are executable Python environments in the spirit of virtualenvs. pex is an expansion upon the ideas outlined in PEP 441 and makes the deployment of Python applications as simple as cp. pex files may even include multiple platform-specific Python distributions, meaning that a single pex file can be portable across Linux and OS X.

pex files can be built using the pex tool. Build systems such as Pants, Buck, and {py}gradle also support building .pex files directly.

Still unsure about what pex does or how it works? Watch this quick lightning talk: WTF is PEX?.

pex is licensed under the Apache2 license.


To install pex, simply

$ pip install pex

You can also build pex in a git clone using tox:

$ tox -e package
$ cp dist/pex ~/bin

This builds a pex binary in dist/pex that can be copied onto your $PATH. The advantage to this approach is that it keeps your Python environment as empty as possible and is more in-line with what pex does philosophically.

Simple Examples

Launch an interpreter with requests, flask and psutil in the environment:

$ pex requests flask 'psutil>2,<3'

Or instead freeze your current virtualenv via requirements.txt and execute it anywhere:

$ pex $(pip freeze) -o my_virtualenv.pex
$ deactivate
$ ./my_virtualenv.pex

Run in an environment containing flask as a quick way to experiment:

$ pex flask --

Launch Sphinx in an ephemeral pex environment using the Sphinx entry point sphinx:main:

$ pex sphinx -e sphinx:main -- --help

Build a standalone pex binary into pex.pex using the pex console_scripts entry point:

$ pex pex -c pex -o pex.pex

You can also build pex files that use a specific interpreter type:

$ pex pex -c pex --python=pypy -o pypy-pex.pex

Most pex options compose well with one another, so the above commands can be mixed and matched. For a full list of options, just type pex --help.

Integrating pex into your workflow

If you use tox (and you should!), a simple way to integrate pex into your workflow is to add a packaging test environment to your tox.ini:

deps = pex
commands = pex . -o dist/app.pex

Then tox -e package will produce a relocateable copy of your application that you can copy to staging or production environments.


More documentation about Pex, building .pex files, and how .pex files work is available at


Pex uses tox for test and development automation. To run the test suite, just invoke tox:

$ tox

If you don’t have tox, you can generate a pex of tox:

$ pex tox -c tox -o ~/bin/tox

Tox provides many useful commands and options, explained at Below, we provide some of the most commonly used commands used when working on Pex, but the docs are worth acquainting yourself with to better understand how Tox works and how to do more advanced commmands.

To run a specific environment, identify the name of the environment you’d like to invoke by running tox --listenvs-all, then invoke like this:

$ tox -e format-run

To run MyPy:

$ tox -e typecheck

All of our tox test environments allow passthrough arguments, which can be helpful to run specific tests:

$ tox -e py37-integration -- -k test_reproducible_build

To run Pex from source, rather than through what is on your PATH, invoke via Python:

$ python -m pex


To contribute, follow these instructions: