Hey! These docs are for version 2.6, which is no longer officially supported. Click here for the latest version, 2.18!


A Python target that can be converted into an executable PEX file.

PEX files are self-contained executable files that contain a complete Python environment capable of running the target. For more information, see Pex files.


type: bool
default: False

Whether PEX should always write the .deps cache of the .pex file to disk or not. This can use less memory in RAM-constrained environments.


type: Iterable[str] | None
default: None

Addresses to other targets that this target depends on, e.g. ['helloworld/subdir:lib'].

Alternatively, you may include file names. Pants will find which target owns that file, and create a new target from that which only includes the file in its sources field. For files relative to the current BUILD file, prefix with ./; otherwise, put the full path, e.g. ['./sibling.txt', 'resources/demo.json'].

You may exclude dependencies by prefixing with !, e.g. ['!helloworld/subdir:lib', '!./sibling.txt']. Ignores are intended for false positives with dependency inference; otherwise, simply leave off the dependency from the BUILD file.


type: str | None
default: None

A human-readable description of the target.

Use ./pants list --documented :: to see all targets with descriptions.


type: bool | None
default: None

Whether or not to emit PEX warnings at runtime.

The default is determined by the option emit_warnings in the [pex-binary-defaults] scope.


type: str

The entry point for the binary, i.e. what gets run when executing ./my_binary.pex.

You can specify a full module like 'path.to.module' and 'path.to.module:func', or use a shorthand to specify a file name, using the same syntax as the sources field:

  1. 'app.py', Pants will convert into the module path.to.app;
  2. 'app.py:func', Pants will convert into path.to.app:func.

You must use the file name shorthand for file arguments to work with this target.

To leave off an entry point, set to ''.


type: 'unzip' | 'venv' | 'zipapp' | None
default: 'zipapp'

The mode the generated PEX file will run in.

The traditional PEX file runs in 'zipapp' mode (See: https://www.python.org/dev/peps/pep-0441/). In general, faster cold start times can be attained using the 'unzip' mode which also has the benefit of allowing standard use of __file__ and filesystem APIs to access code and resources in the PEX.

The fastest execution mode in the steady state is 'venv', which generates a virtual environment from the PEX file on first run, but then achieves near native virtual environment start times. This mode also benefits from a traditional virtual environment sys.path, giving maximum compatibility with stdlib and third party APIs.


type: bool
default: False

Should PEX ignore when it cannot resolve dependencies?


type: bool
default: False

Whether to include Pex tools in the PEX bootstrap code.

With tools included, the generated PEX file can be executed with PEX_TOOLS=1 <pex file> --help to gain access to all the available tools.


type: 'fallback' | 'false' | 'prefer' | None
default: None

Whether to inherit the sys.path (aka PYTHONPATH) of the environment that the binary runs in.

Use false to not inherit sys.path; use fallback to inherit sys.path after packaged dependencies; and use prefer to inherit sys.path before packaged dependencies.


type: Iterable[str] | None
default: None

The Python interpreters this code is compatible with.

Each element should be written in pip-style format, e.g. CPython==2.7.* or CPython>=3.6,<4. You can leave off CPython as a shorthand, e.g. >=2.7 will be expanded to CPython>=2.7.

Specify more than one element to OR the constraints, e.g. ['PyPy==3.7.*', 'CPython==3.7.*'] means either PyPy 3.7 or CPython 3.7.

If the field is not set, it will default to the option [python-setup].interpreter_constraints.

See Interpreter compatibility for how these interpreter constraints are merged with the constraints of dependencies.


type: str | None
default: None

Where the built asset should be located.

If undefined, this will use the path to the BUILD file, followed by the target name. For example, src/python/project:app would be `src.python.project/app.ext.

When running ./pants package, this path will be prefixed by --distdir (e.g. dist/).

Warning: setting this value risks naming collisions with other package targets you may have.


type: Iterable[str] | None
default: None

The platforms the built PEX should be compatible with.

This defaults to the current platform, but can be overridden to different platforms. You can give a list of multiple platforms to create a multiplatform PEX.

To use wheels for specific interpreter/platform tags, you can append them to the platform with hyphens like: PLATFORM-IMPL-PYVER-ABI (e.g. "linux_x86_64-cp-27-cp27mu", "macosx_10.12_x86_64-cp-36-cp36m"):

  • PLATFORM: the host platform, e.g. "linux-x86_64", "macosx-10.12-x86_64".
  • IMPL: the Python implementation abbreviation, e.g. "cp", "pp", "jp".
  • PYVER: a two-digit string representing the Python version, e.g. "27", "36".
  • ABI: the ABI tag, e.g. "cp36m", "cp27mu", "abi3", "none".


type: str | None
default: None

Set the generated PEX to use this shebang, rather than the default of PEX choosing a shebang based on the interpreter constraints.

This influences the behavior of running ./result.pex. You can ignore the shebang by instead running /path/to/python_interpreter ./result.pex.


type: bool
default: True

Whether or not to strip the PEX runtime environment of PEX* environment variables.

Most applications have no need for the PEX* environment variables that are used to control PEX startup; so these variables are scrubbed from the environment by Pex before transferring control to the application by default. This prevents any subprocesses that happen to execute other PEX files from inheriting these control knob values since most would be undesired; e.g.: PEX_MODULE or PEX_PATH.


type: Iterable[str] | None
default: None

Arbitrary strings to describe a target.

For example, you may tag some test targets with 'integration_test' so that you could run ./pants --tag='integration_test' test :: to only run on targets with that tag.


type: bool
default: True

Whether or not this binary is safe to run in compacted (zip-file) form.

If the PEX is not zip safe, it will be written to disk prior to execution. You may need to mark zip_safe=False if you're having issues loading your code.