Py + Deps = <3

peds.py

#!/usr/bin/env python
"""Py + Deps = <3: Simple script to install only dependencies of a python
package which follows PEP-517/PEP-518 guidelines.
"""

from argparse import ArgumentParser, Namespace
from dataclasses import dataclass, field
from pathlib import Path
from subprocess import check_call
from sys import version_info
from tempfile import TemporaryDirectory
from typing import Dict, List

if version_info < (3, 10):
    from tomli import load
else:
    from tomllib import load


parser = ArgumentParser(description=__doc__)
parser.add_argument('-i',
                    '--install',
                    action='store_true',
                    help='install dependencies')
parser.add_argument('-e',
                    '--extras',
                    default=[],
                    type=str,
                    action='append',
                    help='list of optional dependencies to install in advance')
parser.add_argument('--extra-index-url',
                    default=None,
                    type=str,
                    help='extra PyPI index')
parser.add_argument('package_dir',
                    default=Path(),
                    type=Path,
                    help='path to package root')


@dataclass
class Dependencies:

    required: List[str]

    optional: Dict[str, List[str]] = field(default=dict)

    @staticmethod
    def from_package_dir(path: Path) -> 'Dependencies':
        if not path.is_dir():
            raise ValueError(f'Expected directory at {path}.')
        with open(path / 'pyproject.toml', 'rb') as fin:
            config = load(fin)
        project = config.get('project', {})
        required_deps = project.get('dependencies', [])
        optional_deps = project.get('optional-dependencies', {})
        return Dependencies(required_deps, optional_deps)

    def install(self, extras: List[str], extra_opts: List[str] = []):
        with TemporaryDirectory() as tmp_dir:
            path = Path(tmp_dir) / 'requirements.txt'
            self.to_file(path, extras)
            check_call(['pip', 'install', '-r', str(path), *extra_opts])

    def to_file(self, path: Path, extras: List[str] = []):
        def write_deps(fout, deps):
            for dep in deps:
                fout.write(dep)
                fout.write('\n')
        with open(path, 'w') as fout:
            write_deps(fout, self.required)
            for extra in extras:
                if (deps := self.optional.get(extra)) is None:
                    raise KeyError('There is no such extra dependencies '
                                   f'with key {extra}.')
                write_deps(fout, deps)


def format_dependencies(deps: List[str]) -> str:
    if len(deps) == 0:
        return 'n/a'
    return ', '.join(deps)


def main(args: Namespace):
    deps = Dependencies.from_package_dir(args.package_dir)
    if args.install:
        extra_opts = []
        if args.extra_index_url is not None:
            extra_opts += ['--extra-index-url', args.extra_index_url]
        deps.install(args.extras, extra_opts)
    else:
        print('Required:', format_dependencies(deps.required))
        for key, val in deps.optional.items():
            print(f'Optional[{key}]:', format_dependencies(val))


if __name__ == '__main__':
    main(parser.parse_args())