How do I run a custom distutils Command without a setup.py?

[thrau]

Question

Is it still possible to run individual custom distutils commands without a setup.py?

Background

My project https://github.com/localstack/plux provides a way to automatically generate entrypoints from code. Regenerating entrypoints has been very convenient by running python setup.py plugins egg_info, where plugins is a custom setuptools command provided by plux, and egg_info is the setuptools script to generate the .egg-info directory containing the entrypoints.

With the modern way of writing distributions without a setup.py file, and rather moving everything into pyproject.toml and using build, I no longer know how to run individual distutils/setuptools scripts. I can obviously always run pip install -e . again, but i'd really rather provide a command that specifically re-builds the entry_points.txt using the setuptools plumbing I already have.

[abravalheri]

Hi @thrau,

If you want to use commands distributed by setuptools and or distutils outside of the build process, you can still use the programmatic API for that (i.e., creating the Distribution and Command objects, setting up the correct attribute values and calling the relevant methods appropriately).

However, since the Python packaging ecosystem has started to move towards build APIs (instead of CLI calls), the scope of setuptools shrank, and the project no longer has as objective to:

1. Perform direct installation of packages (this is delegated to pip)
2. Maintain CLI capabilities for running commands.

You can read more about this shift in https://blog.ganssle.io/articles/2021/10/setup-py-deprecated.html

[abravalheri]

I think this is an example that is simple to understand:

https://github.com/pypa/setuptools/blob/v69.1.0/setuptools/tests/test_sdist.py#L169-L175

Distribution.parse_config_files, is also useful when your configuration is given via pyproject.toml or setup.cfg.

[thrau]

well, at least that gives me a starting point, thank you! i'll play around with this to see whether it answers my question. :-)

[abravalheri]

I believe that you can also run commands with dist.run_command("name").

[thrau]

Based on the hints you provided, I came up with something (conceptually) like this to replace the python setup.py plugins egg_info command:

import os
from setuptools.dist import Distribution

workdir = os.getcwd()

# prepare Distribution from workdir
config_files = ["pyproject.toml", "setup.cfg"]
config_files = [file for file in config_files if os.path.exists(file)]

if not config_files:
    raise ValueError(f"no distribution config files found in {workdir}")

dist = Distribution()
dist.parse_config_files(config_files)
if os.path.exists("setup.py"):
    # use setup.py script if available
    dist.script_name = os.path.join(workdir, "setup.py")
else:
    # else use a bogus file (seems to work regardless)
    dist.script_name = config_files[0]

# run commands
dist.run_command("plugins")
dist.run_command("egg_info")