w00t, switch/case does something useful

parse_package_metadata.py

from collections import defaultdict
import importlib.metadata
from typing import Any
from pprint import pp

from packaging.requirements import Requirement
from packaging.markers import Op, Value, Variable


def group_deps_by_extra(pkg: str) -> dict[str, list[str]]:
    """Query metadata of an installed package for extra-install-dependencies."""
    dists = importlib.metadata.metadata(pkg).get_all("Requires-Dist", [])  # list of pep 508 strings

    ret = defaultdict(list)
    for dist in map(Requirement, dists):
        if dist.marker is None:
            continue
        for marker in dist.marker._markers:
            if (extra := get_extra(marker)) is not None:
                ret[extra].append(dist.name)
    return {**ret}


def get_extra_3_9(marker: Any) -> str | None:
    # ugh...
    if isinstance(marker, tuple) and len(marker) == 3:
        var, op, val = marker
        if (
            isinstance(var, Variable)
            and isinstance(op, Op)
            and isinstance(val, Value)
        ):
            if var.value == "extra" and op.value == "==":
                return val.value
    # shorter alternatives are more bug-prone and may raise ~5 types of exceptions


def get_extra_3_10(marker: Any) -> str | None:
    # a lot more readable
    match marker:
        case (Variable(value="extra"), Op(value="=="), Value(value=extra)):
            return extra


get_extra = get_extra_3_9  # result is the same with `get_extra_3_10`

if __name__ == '__main__':
    pp(group_deps_by_extra("fastapi"))  # has a coupe of interesting extras

run.txt

# output with fastapi-0.95.1
{'all': ['email-validator',
         'httpx',
         'itsdangerous',
         'jinja2',
         'orjson',
         'python-multipart',
         'pyyaml',
         'ujson',
         'uvicorn'],
 'dev': ['pre-commit', 'ruff', 'uvicorn'],
 'doc': ['mdx-include',
         'mkdocs-markdownextradata-plugin',
         'mkdocs-material',
         'mkdocs',
         'pyyaml',
         'typer-cli',
         'typer'],
 'test': ['anyio',
          'black',
          'coverage',
          'databases',
          'email-validator',
          'flask',
          'httpx',
          'isort',
          'mypy',
          'orjson',
          'passlib',
          'peewee',
          'pytest',
          'python-jose',
          'python-multipart',
          'pyyaml',
          'ruff',
          'sqlalchemy',
          'types-orjson',
          'types-ujson',
          'ujson']}