Building .pex files

You can build .pex files using the pex utility, which is made available when you pip install pex. Do this within a virtualenv, then you can use pex to bootstrap itself:

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

This command creates a pex file containing pex, using the console script named “pex”, saving it in ~/bin/pex. At this point, assuming ~/bin is on your $PATH, then you can use pex in or outside of any virtualenv.

This is described in more detail below.

Invoking the pex utility

The pex utility has no required arguments and by default will construct an empty environment and invoke it. When no entry point is specified, “invocation” means starting an interpreter:

$ pex
Pex 2.16.1 ephemeral hermetic environment with no dependencies.
Exit the repl (type quit()) and run `pex -h` for Pex CLI help.
Python 3.11.9 (main, Apr 26 2024, 19:20:24) [GCC 13.2.0] on linux
Type "help", "pex", "copyright", "credits" or "license" for more information.
>>>

This creates an ephemeral environment that only exists for the duration of the pex command invocation and is garbage collected immediately on exit.

You can tailor which interpreter is used by specifying --python=PATH. PATH can be either the absolute path of a Python binary or the name of a Python interpreter within the environment, e.g.:

$ pex
Pex 2.16.1 ephemeral hermetic environment with no dependencies.
Exit the repl (type quit()) and run `pex -h` for Pex CLI help.
Python 3.11.9 (main, Apr 26 2024, 19:20:24) [GCC 13.2.0] on linux
Type "help", "pex", "copyright", "credits" or "license" for more information.
>>> print "This won't work!"
  File "<console>", line 1
    print "This won't work!"
    ^^^^^^^^^^^^^^^^^^^^^^^^
SyntaxError: Missing parentheses in call to 'print'. Did you mean print(...)?
>>>
$ pex --python=python2.7
Pex 2.16.1 ephemeral hermetic environment with no dependencies.
Python 2.7.18 (default, Apr 26 2024, 19:14:20)
[GCC 13.2.0] on linux2
Type "help", "pex", "copyright", "credits" or "license" for more information.
>>> print "This works."
This works.
>>>

Specifying requirements

Requirements are specified using the same form as expected by pip and setuptools, e.g. flask, setuptools==2.1.2, Django>=1.4,<1.6. These are specified as arguments to pex and any number (including 0) may be specified. For example, to start an environment with flask and psutil>1:

$ pex flask 'psutil>1'
Pex 2.16.1 ephemeral hermetic environment with 2 requirements and 8 activated distributions.
Python 3.11.9 (main, Apr 26 2024, 19:20:24) [GCC 13.2.0] on linux
Type "help", "pex", "copyright", "credits" or "license" for more information.
>>>

You can then import and manipulate modules like you would otherwise:

>>> import flask
>>> import psutil
>>> ...

Conveniently, the output of pip freeze (a list of pinned dependencies) can be passed directly to pex. This provides a handy way to freeze a virtualenv into a PEX file.

$ pex $(pip freeze) -o my_application.pex

A requirements.txt file may also be used, just as with pip.

$ pex -r requirements.txt -o my_application.pex

Specifying entry points

Entry points define how the environment is executed and may be specified in one of three ways.

pex <options> – script.py

As mentioned above, if no entry points are specified, the default behavior is to emulate an interpreter. First we create a simple flask application:

$ cat <<EOF > flask_hello_world.py
from flask import Flask
app = Flask(__name__)

@app.route('/')
def hello_world():
    return 'hello world!'

app.run()
EOF

Then, like an interpreter, if a source file is specified as a parameter to pex, it is invoked:

$ pex flask -- ./flask_hello_world.py
 * Serving Flask app '__main__'
 * Debug mode: off
WARNING: This is a development server. Do not use it in a production deployment. Use a production WSGI server instead.
 * Running on http://127.0.0.1:5000
Press CTRL+C to quit

pex -m

Your code may be within the PEX file or it may be some predetermined entry point within the standard library. pex -m behaves very similarly to python -m. Consider python -m pydoc:

$ python -m pydoc
pydoc - the Python documentation tool

pydoc <name> ...
    Show text documentation on something.  <name> may be the name of a
    Python keyword, topic, function, module, or package, or a dotted
    reference to a class or function within a module or module in a
    ...

This can be emulated using the pex tool using -m pydoc:

$ pex -m pydoc
pydoc - the Python documentation tool

pydoc <name> ...
    Show text documentation on something.  <name> may be the name of a
    Python keyword, topic, function, module, or package, or a dotted
    reference to a class or function within a module or module in a
    ...

Arguments will be passed unescaped following -- on the command line. So in order to get pydoc help on the flask.app package in Flask:

$ TERM=dumb pex flask -m pydoc -- flask.app
Help on module flask.app in flask:

NAME
    flask.app

CLASSES
    flask.sansio.app.App(flask.sansio.scaffold.Scaffold)
        Flask

    class Flask(flask.sansio.app.App)
...

and so forth.

Entry points can also take the form package:target, such as sphinx:main or fabric.main:main for Sphinx and Fabric respectively. This is roughly equivalent to running a script that does import sys, from package import target; sys.exit(target()).

This can be a powerful way to invoke Python applications without ever having to pip install anything, for example a one-off invocation of Sphinx with the readthedocs theme available:

$ pex --python python2.7 sphinx==1.2.2 sphinx_rtd_theme==0.1.6 -e sphinx:main -- --help
Sphinx v1.2.2
Usage: /tmp/tmp19tsy1r0 [options] sourcedir outdir [filenames...]

General options
^^^^^^^^^^^^^^^
-b <builder>  builder to use; default is html
-a            write all files; default is to only write new and changed files
-E            don't use a saved environment, always read all files
...

Although sys.exit is applied blindly to the return value of the target function, this probably does what you want due to very flexible sys.exit semantics. Consult your target function and sys.exit documentation to be sure.

Almost certainly better and more stable, you can alternatively specify a console script exported by the app as explained below.

pex -c

If you don’t know the package:target for the console scripts of your favorite python packages, pex allows you to use -c to specify a console script as defined by the distribution. For example, Fabric provides the fab tool when pip installed:

$ pex Fabric -c fab -- --help
Usage: tmpm_gu_7vf [--core-opts] task1 [--task1-opts] ... taskN [--taskN-opts]

Core options:

  --complete                         Print tab-completion candidates for given parse remainder.
...

Even scripts defined by the “scripts” section of a distribution can be used, e.g. with boto:

$ python2.7 -mpex boto -c mturk
usage: mturk [-h] [-P] [--nicknames PATH]
             {bal,hit,hits,new,extend,expire,rm,as,approve,reject,unreject,bonus,notify,give-qual,revoke-qual}
             ...
mturk: error: too few arguments

Note: If you run pex -c and come across an error similar to pex.pex_builder.InvalidExecutableSpecification: Could not find script 'mainscript.py' in any distribution within PEX!, double-check your setup.py and ensure that mainscript.py is included in your setup’s scripts array. If you are using console_scripts and run into this error, double check your console_scripts syntax - further information for both scripts and console_scripts can be found in the Python packaging documentation.

Saving .pex files

Each of the commands above have been manipulating ephemeral PEX environments – environments that only exist for the duration of the pex command lifetime and immediately garbage collected.

If the -o PATH option is specified, a PEX file of the environment is saved to disk at PATH. For example we can package a standalone Sphinx as above:

$ pex ansible -c ansible -o ansible.pex

Instead of executing the environment, it is saved to disk:

$ ls -l ansible.pex
-rwxr-xr-x 1 jsirois jsirois 58424496 Aug 13 11:39 ansible.pex

This is an executable environment and can be executed as before:

$ ./ansible.pex --help
usage: ansible [-h] [--version] [-v] [-b] [--become-method BECOME_METHOD]
               [--become-user BECOME_USER]
               [-K | --become-password-file BECOME_PASSWORD_FILE]
               [-i INVENTORY] [--list-hosts] [-l SUBSET] [-P POLL_INTERVAL]
               [-B SECONDS] [-o] [-t TREE] [--private-key PRIVATE_KEY_FILE]
               [-u REMOTE_USER] [-c CONNECTION] [-T TIMEOUT]
               [--ssh-common-args SSH_COMMON_ARGS]
               [--sftp-extra-args SFTP_EXTRA_ARGS]
               [--scp-extra-args SCP_EXTRA_ARGS]
               [--ssh-extra-args SSH_EXTRA_ARGS]
               [-k | --connection-password-file CONNECTION_PASSWORD_FILE] [-C]
               [-D] [-e EXTRA_VARS] [--vault-id VAULT_IDS]
               [-J | --vault-password-file VAULT_PASSWORD_FILES] [-f FORKS]
               [-M MODULE_PATH] [--playbook-dir BASEDIR]
               [--task-timeout TASK_TIMEOUT] [-a MODULE_ARGS] [-m MODULE_NAME]
               pattern

Define and run a single task 'playbook' against a set of hosts

positional arguments:
  pattern               host pattern

options:
  --become-password-file BECOME_PASSWORD_FILE, --become-pass-file BECOME_PASSWORD_FILE
                        Become password file
...

As before, entry points are not required, and if not specified the PEX will default to just dropping into an interpreter. If an alternate interpreter is specified with --python, e.g. pypy, it will be the default hashbang in the PEX file:

$ pex --python=pypy3.10 flask -o flask-pypy.pex

The hashbang of the PEX file specifies PyPy:

$ head -1 flask-pypy.pex
#!/usr/bin/env pypy3.10

and when invoked uses the environment PyPy:

:; ./flask-pypy.pex
Pex 2.16.1 hermetic environment with 1 requirement and 7 activated distributions.
Python 3.10.14 (75b3de9d9035, Apr 21 2024, 10:54:48)
[PyPy 7.3.16 with GCC 10.2.1 20210130 (Red Hat 10.2.1-11)] on linux
Type "help", "pex", "copyright", "credits" or "license" for more information.
>>> import flask
>>>

To specify an explicit Python shebang line (e.g. from a non-standard location or not on $PATH), you can use the --python-shebang option:

$ pex --python-shebang='/Users/wickman/Python/CPython-3.4.2/bin/python3.4' -o my.pex
$ head -1 my.pex
#!/Users/wickman/Python/CPython-3.4.2/bin/python3.4

Furthermore, this can be manipulated at runtime using the PEX_PYTHON environment variable.

Tailoring requirement resolution

In general, pex honors the same options as pip when it comes to resolving packages. Like pip, by default pex fetches artifacts from PyPI. This can be disabled with --no-index.

If PyPI fetching is disabled, you will need to specify a search repository via -f/--find-links. This may be a directory on disk or a remote simple http server.

For example, you can delegate artifact fetching and resolution to pip wheel for whatever reason – perhaps you’re running a firewalled mirror – but continue to package with pex:

$ pip wheel -w /tmp/wheelhouse sphinx sphinx_rtd_theme setuptools
$ pex -f /tmp/wheelhouse --no-index -c sphinx-build -o sphinx.pex sphinx sphinx_rtd_theme setuptools

Tailoring PEX execution at build time

There are a few options that can tailor how PEX environments are invoked. These can be found by running pex --help. Every flag mentioned here has a corresponding environment variable that can be used to override the runtime behavior which can be set directly in your environment, or sourced from a .pexrc file (checking for ~/.pexrc first, then for a relative .pexrc).

--inherit-path

By default, PEX environments are completely scrubbed empty of any packages installed on the global site path. Setting --inherit-path allows packages within site-packages to be considered as candidate distributions to be included for the execution of this environment. This is strongly discouraged as it circumvents one of the biggest benefits of using .pex files, however there are some cases where it can be advantageous (for example if a package does not package correctly an an egg or wheel.)

--ignore-errors

If not all of the PEX environment’s dependencies resolve correctly (e.g. you are overriding the current Python interpreter with PEX_PYTHON) this forces the PEX file to execute despite this. Can be useful in certain situations when particular extensions may not be necessary to run a particular command.

--platform

The (abbreviated) platform to build the PEX for. This will look for wheels for the particular platform.

The abbreviated platform is described by a string of the form PLATFORM-IMPL-PYVER-ABI, where PLATFORM is the platform (e.g. linux-x86_64, macosx-10.4-x86_64), IMPL is the python implementation abbreviation (cp or pp), PYVER is either a two or more digit string representing the python version (e.g., 36 or 310) or else a component dotted version string (e.g., 3.6 or 3.10.1) and ABI is the ABI tag (e.g., cp36m, cp27mu, abi3, none). A complete example: linux_x86_64-cp-36-cp36m.

Constraints: when --platform is used the environment marker python_full_version will not be available if PYVER is not given as a three component dotted version since python_full_version is meant to have 3 digits (e.g., 3.8.10). If a python_full_version environment marker is encountered during a resolve, an UndefinedEnvironmentName exception will be raised. To remedy this, either specify the full version in the platform (e.g, linux_x86_64-cp-3.8.10-cp38) or use --complete-platform instead.

--complete-platform

The completely specified platform to build the PEX for. This will look for wheels for the particular platform.

The complete platform can be either a path to a file containing JSON data or else a JSON object literal. In either case, the JSON object is expected to have two fields with any other fields ignored. The marker_environment field should have an object value with string field values corresponding to PEP-508 marker environment entries. It is OK to only have a subset of valid marker environment fields but it is not valid to present entries not defined in PEP-508. The compatible_tags field should have an array of strings value containing the compatible tags in order from most specific first to least specific last as defined in PEP-425. Pex can create complete platform JSON for you by running it on the target platform like so: pex3 interpreter inspect --markers --tags. For more options, particularly to select the desired target interpreter see: pex3 interpreter inspect --help.

Tailoring PEX execution at runtime

Tailoring of PEX execution can be done at runtime by setting various environment variables. See PEX runtime environment variables.

Using bdist_pex

pex provides a convenience command for use in setuptools. python setup.py bdist_pex is a simple way to build executables for Python projects that adhere to standard naming conventions.

bdist_pex

The default behavior of bdist_pex is to build an executable using the console script of the same name as the package. For example, pip has three entry points: pip, pip2 and pip2.7 if you’re using Python 2.7. Since there exists an entry point named pip in the console_scripts section of the entry points, that entry point is chosen and an executable pex is produced. The pex file will have the version number appended, e.g. pip-7.2.0.pex.

If no console scripts are provided, or the only console scripts available do not bear the same name as the package, then an environment pex will be produced. An environment pex is a pex file that drops you into an interpreter with all necessary dependencies but stops short of invoking a specific module or function.

bdist_pex --bdist-all

If you would like to build all the console scripts defined in the package instead of just the namesake script, --bdist-all will write all defined entry_points but omit version numbers and the .pex suffix. This can be useful if you would like to virtually install a Python package somewhere on your $PATH without doing something scary like sudo pip install:

$ git clone https://github.com/sphinx-doc/sphinx && cd sphinx
$ python setup.py bist_pex --bdist-all --bdist-dir=$HOME/bin
running bdist_pex
Writing sphinx-apidoc to /Users/wickman/bin/sphinx-apidoc
Writing sphinx-build to /Users/wickman/bin/sphinx-build
Writing sphinx-quickstart to /Users/wickman/bin/sphinx-quickstart
Writing sphinx-autogen to /Users/wickman/bin/sphinx-autogen
$ sphinx-apidoc --help | head -1
Usage: sphinx-apidoc [options] -o <output_path> <module_path> [exclude_path, ...]

Using Pants

The Pants build system can build pex files. See here for details.