run
Run a pex_binary target.
To run an executable/script, use pants run on one of the following target types:
(See package for more on the pex_binary target.)
# A python_source target (usually referred to by the filename)
$ pants run project/app.py
or
# A pex_binary target (must be referred to by target name)
$ pants run project:app
To pass arguments to the script/executable, use -- at the end of the command, like this:
$ pants run project/app.py -- --arg1 arg2
You may only run one target at a time.
The program will have access to the same environment used by the parent pants process, so you can set environment variables in the external environment, e.g. FOO=bar pants run project/app.py. (Pants will auto-set some values like $PATH).
Pants will propagate the return code from the underlying executable. Run echo $? after the Pants run to see the return code.
Run pants dependencies --transitive path/to/binary.py to ensure that all the files you need are showing up, including for any assets you intend to use.
Execution Semantics
Running a pex_binary is equivalent to package-ing the target followed by executing the built PEX from the repo root.
Running a python_source with the run_goal_use_sandbox field set to True (the default) runs your code in an ephemeral sandbox (temporary directory) with your firstparty code and Pants-generated files (such as a relocated_files or archive) copied inside. If you are using generated files like this, you may need to set the run_goal_use_sandbox to True for file loading to work properly.
Running a python_source with the run_goal_use_sandbox field set to False is equivalent to running the source directly (a la python ...) with the set of third-party dependencies exposed to the interpreter. This is comparable to using a virtual environment or Poetry to run your script (E.g. venv/bin/python ... or poetry run python ...). When scripts write in-repo files—such as Django's manage.py makemigrations - it is often necessary to set run_goal_use_sandbox to False so that the file is written into the expected location.
Watching the filesystem
If the app that you are running is long-lived and safe to restart (including web apps like Django and Flask or other types of servers/services), you can set restartable=True on your pex_binary target to indicate this to Pants. The run goal will then automatically restart the app when its input files change!
On the other hand, if your app is short-lived (like a script) and you'd like to re-run it when files change but never interrupt an ongoing run, consider using pants --loop run instead. See Goals for more information on --loop.
Debugging
- In your editor, set your breakpoints and any other debug settings (like break-on-exception).
- Run your code with
pants run --debug-adapter. - Connect your editor to the server. The server host and port are logged by Pants when executing
run --debug-adapter. (They can also be configured using the[debug-adapter]subsystem).
First, add the following target in some BUILD file (e.g., the one containing your other 3rd-party dependencies):
python_requirement(
name = "pydevd-pycharm",
requirements=["pydevd-pycharm==203.5419.8"], # Or whatever version you choose.
)
You can check this into your repo, for convenience.
Now, use the remote debugger as usual:
- Start a Python remote debugging session in PyCharm, say on port 5000.
- Add the following code at the point where you want execution to pause and connect to the debugger:
import pydevd_pycharm
pydevd_pycharm.settrace('localhost', port=5000, stdoutToServer=True, stderrToServer=True)
Run your executable with pants run as usual.
Note: The first time you do so you may see some extra dependency resolution work, as pydevd-pycharm has now been added to the binary's dependencies, via inference. If you have dependency inference turned off in your repo, you will have to manually add a temporary explicit dependency in your binary target on the pydevd-pycharm target.