Implement parsing of default command configuration from `pyproject.toml` by max-moser · Pull Request #1290 · python-babel/babel

max-moser · 2026-07-07T13:36:38Z

I believe this should close #777

This PR adds support of pyproject.toml as a source for default configuration values for the various CLI commands (compile, extract, init, update).
The configuration will be read from pyproject.toml, under the [tool.babel.<command_name>] table, where <command_name> is one of compile_catalog, extract_messages, init_catalog, update_catalog (taken from frontend_setuptools).

The motivation for this PR here is that I've recently migrated most of the inveniosoftware packages from setuptools to hatchling and we included the old configuration from setup.cfg in pyproject.toml, only to find that pybabel doesn't actually read any command config from pyproject.toml 😅
(Luckily for us that was only a minor issue in one package that we fixed otherwise)

The mechanism for finding pyproject.toml is similar to that used in other tools, like isort.
I could also imagine adding a global CLI flag for disabling reading pyproject.toml altogether, or for letting users specify another TOML config file instead.

The parsed values are inserted as default values for the optparse parser, so user-provided CLI flags should still take precedence.

Please let me know if this goes in an acceptable direction, then I can polish up the implementation a bit 🙂

akx

This would require tests -- oh and what happens if this finds a pyproject.toml that doesn't have tool.babel?

max-moser · 2026-10-30T09:54:17Z

Thanks for the review, I'll spruce up the PR a bit. 🙂

If present, use a "pyproject.toml" file for default configuration of `pybabel` commands.

max-moser

I've touched up the PR a bit to address your feedback (especially the case when the section is missing from pyproject.toml) and generally touched up the implementation a little bit (with type hints and such).

There's now a test case for the config parsing itself, and one for the extract_messages CLI command that basically emulates what another test did, but with the config coming from pyproject.toml instead of CLI args.

max-moser · 2026-10-30T12:11:28Z

        if cmdname not in self.commands:
            self.parser.error(f'unknown command "{cmdname}"')

+        # TODO add possibility to turn TOML config parsing off, e.g. new option above?


@akx thoughts & prayers?

Yeah... at the very least I think we should fail gracefully here if there's e.g. a malformed pyproject.toml somewhere up the directory hierarchy?

akx

Thanks! Some comments -- this is looking pretty good.

I think we might want a BABEL_NO_PYPROJECT_TOML escape hatch for now?

akx · 2026-11-04T06:21:12Z

+    The ``style`` can be either "pyproject.toml" or "standalone", and dictates
+    the sections/tables in the TOML file that will be used.
+    The ``filename`` will be used in error messages.
+    If ``allow_missing_sections`` is set and the TOML file doesn't have a
+    ``[tool.babel]`` section, an empty dictionary will be returned instead of raising
+    a ``ConfigurationError``.


Could we use the standard :param: , etc. docstring markers here?

akx · 2026-11-04T06:21:52Z

+    style: Literal["standalone", "pyproject.toml"],
+    filename: str = "(unknown)",
+    allow_missing_sections: bool = False,


Let's make the rest of these args kwarg-only:

Suggested change

style: Literal["standalone", "pyproject.toml"],

filename: str = "(unknown)",

allow_missing_sections: bool = False,

*,

style: Literal["standalone", "pyproject.toml"],

filename: str = "(unknown)",

allow_missing_sections: bool = False,

akx · 2026-11-04T06:22:09Z

+    return babel_data
+
+
+def find_pyproject_toml(path: pathlib.Path | None, max_depth=10) -> pathlib.Path | None:


Suggested change

def find_pyproject_toml(path: pathlib.Path | None, max_depth=10) -> pathlib.Path | None:

def find_pyproject_toml(path: pathlib.Path | None, max_depth: int = 10) -> pathlib.Path | None:

akx · 2026-11-04T06:23:50Z

+def find_pyproject_toml(path: pathlib.Path | None, max_depth=10) -> pathlib.Path | None:
+    """Find the closest "pyproject.toml" file to the specified path.
+
+    If the path already points to a "pyproject.toml" file, return it.


Is this function ever expected to actually be called with a direct pyproject.toml path? Currently doesn't look like it, so I'd maybe get rid of that logic?

akx · 2026-11-04T06:24:43Z

+    tries = 0
+    while tries < max_depth:
+        pyproject_file = path / "pyproject.toml"
+        if pyproject_file.exists():


Maybe:

Suggested change

if pyproject_file.exists():

if pyproject_file.is_file():

akx · 2026-11-04T06:30:26Z

            else:
                parser.add_option(*strs, help=help, default=default, choices=choices)
+
+        parser.set_defaults(**toml_config)


Why is this separately necessary? 🤔

akx · 2026-11-04T06:30:44Z

+            # use the TOML config as fallback if args isn't set
+            args = args or toml_config.get(as_args.replace("-", "_"), args)


akx · 2026-11-04T06:32:43Z

+    """
+    Fixture to create ``${data_dir}/pyproject.toml`` and clean it after the test.
+    """
+    pyproject_toml = (pathlib.Path(data_dir) / "pyproject.toml")
+    pyproject_toml.touch()
+    yield pyproject_toml
+    pyproject_toml.unlink()


This will cause race conditions when tests are being run in parallel with e.g. pytest-xdist.

See e.g. the pot_file fixture that uses tmp_path - could we do something like that here?

akx · 2026-11-04T06:34:17Z

+
+def test_parse_pyproject_toml_config_without_pyproject_toml_file(tmp_path):
+    """
+    Test that trying to parse the config from a missing ``pyproject.toml`` doesn't crash.


This too could fail in the esoteric case that someone has a stray pyproject.toml somewhere in their tmp hierarchy... but maybe we'll take that chance.

akx · 2026-11-04T06:34:44Z

+    """
+    (tmp_path / "pyproject.toml").write_text(pyproject_toml_content)
+    assert frontend.parse_pyproject_toml_config(tmp_path, "extract_messages") == expected
+    (tmp_path / "pyproject.toml").unlink()


Suggested change

(tmp_path / "pyproject.toml").unlink()

No need, tmp_path will be nuked by pytest anyhow.

max-moser force-pushed the mm/pyproject-config branch from 65a5cdb to ceb1f4b Compare July 7, 2026 14:34

akx self-assigned this Jul 7, 2026

akx added the feature label Jul 7, 2026

max-moser force-pushed the mm/pyproject-config branch from ceb1f4b to 511f10d Compare July 11, 2026 08:47

akx added this to the Babel 2.19 milestone Aug 14, 2026

akx force-pushed the mm/pyproject-config branch from 511f10d to da57261 Compare October 30, 2026 09:11

akx requested changes Oct 30, 2026

View reviewed changes

max-moser force-pushed the mm/pyproject-config branch from da57261 to a39395c Compare October 30, 2026 10:46

Implement parsing of command configuration from pyproject.toml

af58d33

If present, use a "pyproject.toml" file for default configuration of `pybabel` commands.

max-moser force-pushed the mm/pyproject-config branch from a39395c to af58d33 Compare October 30, 2026 11:07

Add tests for the configuration parsing from pyproject.toml

8bcec80

max-moser commented Oct 30, 2026

View reviewed changes

akx requested changes Nov 4, 2026

View reviewed changes

		return babel_data


		def find_pyproject_toml(path: pathlib.Path \| None, max_depth=10) -> pathlib.Path \| None:

		# use the TOML config as fallback if args isn't set
		args = args or toml_config.get(as_args.replace("-", "_"), args)

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max-moser commented Jul 7, 2026

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max-moser commented Oct 30, 2026

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