Solution to check if a requirement is met without pkg_resources

[HansBug]

Problem description

In the previous pkg_resources package, this issue can be solved with the following code (link):

import pkg_resources
from pkg_resources import DistributionNotFound, VersionConflict

# dependencies can be any iterable with strings, 
# e.g. file line-by-line iterator
dependencies = [
  'Werkzeug>=0.6.1',
  'Flask>=0.9',
]

# here, if a dependency is not met, a DistributionNotFound or VersionConflict
# exception is thrown. 
pkg_resources.require(dependencies)

However, pkg_resources has been deprecated, so this method is not recommended for continued use. In the migration guide provided in the importlib_metadata documentation, there is no new interface that is completely equivalent to pkg_resources.require. Therefore, we need to use the import_metadata library (native in Python 3.8 or higher) and the packaging library to achieve this functionality.

I have currently implemented a version, the code is here: https://github.com/HansBug/hbutils/blob/main/hbutils/system/python/package.py#L202, where the most critical part is the _yield_reqs_to_install function, which checks a requirement and its sub-requirements included in its extra one by one, and enumerates the unsatisfied requirements. By calling this iterator function, the check of whether a requirement is satisfied can be achieved. This is the core code of the function:

def _yield_reqs_to_install(req: Requirement, current_extra: str = ''):
    if req.marker and not req.marker.evaluate({'extra': current_extra}):
        return

    try:
        version = importlib_metadata.distribution(req.name).version
    except importlib_metadata.PackageNotFoundError:  # req not installed
        yield req
    else:
        if req.specifier.contains(version):
            for child_req in (importlib_metadata.metadata(req.name).get_all('Requires-Dist') or []):
                child_req_obj = Requirement(child_req)

                need_check, ext = False, None
                for extra in req.extras:
                    if child_req_obj.marker and child_req_obj.marker.evaluate({'extra': extra}):
                        need_check = True
                        ext = extra
                        break

                if need_check:  # check for extra reqs
                    yield from _yield_reqs_to_install(child_req_obj, ext)

        else:  # main version not match
            yield req

def check_reqs(reqs: List[str]) -> bool:
    """
    Overview:
        Check if the given requirements are all satisfied.

    :param reqs: List of requirements.
    :return satisfied: All the requirements in ``reqs`` satisfied or not.

    Examples::
        >>> from hbutils.system import check_reqs
        >>> check_reqs(['pip>=20.0'])
        True
        >>> check_reqs(['pip~=19.2'])
        False
        >>> check_reqs(['pip>=20.0', 'setuptools>=50.0'])
        True

    .. note::
        If a requirement's marker is not satisfied in this environment,
        **it will be ignored** instead of return ``False``.
    """
    return all(map(lambda x: _check_req(Requirement(x)), reqs))

Of course, if you need this function immediately, you can simply

pip install hbutils>=0.9.0

and then

from hbutils.system import check_reqs
print(check_reqs(['pip>=20.0']))
print(check_reqs(['pip~=19.2']))
print(check_reqs(['pip>=20.0', 'setuptools>=50.0']))

hbutils is a universal toolkit library containing various common functions, and the project address is https://github.com/HansBug/hbutils. It will be maintained for a long time.

[HansBug]

From python/importlib_metadata#450

[smheidrich]

@HansBug Hi! I'm currently trying to get some information about how to best detect & handle missing extras / optional dependencies at runtime into the PyPA's packaging guide (pypa/packaging.python.org#1606) and your check_reqs is the only modern alternative to pkg_resources.require I know of.

The current draft links to both this issue and your hbutils package, but it feels a bit weird to recommend a "giant toolbox of stuff"-type package for this one function. I'm wondering if you'd be open in principle to splitting it off into its own package? If you don't want to do it yourself, I could also do it & make you maintainer afterwards.

Not saying that it should be done now, because it's still possible that PyPA's reviewers will decide the guide shouldn't include this information at all, in which case it'd be pointless effort - but I thought I'd ask here & give a heads-up before making promises over there.