Get distribution package extras requirements with importlib_metadata library.

get_package_extras.py

import pprint
import re

from collections import defaultdict
from functools import partial
from importlib_metadata import metadata


__semicolon_split = partial(str.split, sep=r';', maxsplit=1)

__package_split = re.compile(r'(?P<name>[^\s!~<>=(]+)\s*(?P<requirements>.*)')
__extra_re = re.compile(r'extra\s*==\s*\'(?P<name>\w+)\'')


def get_extras(dist_name: str) -> dict[str | None, list[tuple[str, str]]]:
    requirements = defaultdict(list)
    for g, key in ((__package_split.fullmatch(p).groups(),
                    (match := __extra_re.search((e or [r''])[0])) and match[r'name'])
                   for p, *e in map(__semicolon_split, metadata(dist_name).get_all(r'Requires-Dist')) ):
        requirements[key].append(g)

    return requirements


pprint.pp(get_extras('fastapi'))