How to use the pip._vendor.pkg_resources function in pip

def should_warn(current_version, removal_version):
    # Our Significant digits on versions is 2, so remove everything but the
    #   first two places.
    current_version = ".".join(current_version.split(".")[:2])
    removal_version = ".".join(removal_version.split(".")[:2])

    # Our warning threshold is one minor version before removal, so we
    #   decrement the minor version by one
    major, minor = removal_version.split(".")
    minor = str(int(minor) - 1)
    warn_version = ".".join([major, minor])

    # Test if our current_version should be a warn
    return (pkg_resources.parse_version(current_version)
                < pkg_resources.parse_version(warn_version))

def wheel_version(source_dir):
    """
    Return the Wheel-Version of an extracted wheel, if possible.

    Otherwise, return False if we couldn't parse / extract it.
    """
    try:
        dist = [d for d in pkg_resources.find_on_path(None, source_dir)][0]

        wheel_data = dist.get_metadata('WHEEL')
        wheel_data = Parser().parsestr(wheel_data)

        version = wheel_data['Wheel-Version'].strip()
        version = tuple(map(int, version.split('.')))
        return version
    except:
        return False

def wheel_version(source_dir):
    # type: (Optional[str]) -> Optional[Tuple[int, ...]]
    """Return the Wheel-Version of an extracted wheel, if possible.
    Otherwise, return None if we couldn't parse / extract it.
    """
    try:
        dist = [d for d in pkg_resources.find_on_path(None, source_dir)][0]

        wheel_data = dist.get_metadata('WHEEL')
        wheel_data = Parser().parsestr(wheel_data)

        version = wheel_data['Wheel-Version'].strip()
        version = tuple(map(int, version.split('.')))
        return version
    except Exception:
        return None

if editables_only:
        def editables_only_test(d):
            return dist_is_editable(d)
    else:
        def editables_only_test(d):
            return True

    if user_only:
        user_test = dist_in_usersite
    else:
        def user_test(d):
            return True

    # because of pkg_resources vendoring, mypy cannot find stub in typeshed
    return [d for d in pkg_resources.working_set  # type: ignore
            if local_test(d) and
            d.key not in skip and
            editable_test(d) and
            editables_only_test(d) and
            user_test(d)
            ]

with this requirement, and set self.satisfied_by or
        self.should_reinstall appropriately.
        """
        if self.req is None:
            return
        # get_distribution() will resolve the entire list of requirements
        # anyway, and we've already determined that we need the requirement
        # in question, so strip the marker so that we don't try to
        # evaluate it.
        no_marker = Requirement(str(self.req))
        no_marker.marker = None
        try:
            self.satisfied_by = pkg_resources.get_distribution(str(no_marker))
        except pkg_resources.DistributionNotFound:
            return
        except pkg_resources.VersionConflict:
            existing_dist = pkg_resources.get_distribution(
                self.req.name
            )
            if use_user_site:
                if dist_in_usersite(existing_dist):
                    self.should_reinstall = True
                elif (running_under_virtualenv() and
                        dist_in_site_packages(existing_dist)):
                    raise InstallationError(
                        "Will not install to the user site because it will "
                        "lack sys.path precedence to {} in {}".format(
                            existing_dist.project_name, existing_dist.location)
                    )
            else:
                self.should_reinstall = True
        else:

def check_if_exists(self):
        """Find an installed distribution that satisfies or conflicts
        with this requirement, and set self.satisfied_by or
        self.conflicts_with appropriately.
        """
        if self.req is None:
            return False
        try:
            self.satisfied_by = pkg_resources.get_distribution(self.req)
        except pkg_resources.DistributionNotFound:
            return False
        except pkg_resources.VersionConflict:
            existing_dist = pkg_resources.get_distribution(
                self.req.project_name
            )
            if self.use_user_site:
                if dist_in_usersite(existing_dist):
                    self.conflicts_with = existing_dist
                elif (running_under_virtualenv() and
                        dist_in_site_packages(existing_dist)):
                    raise InstallationError(
                        "Will not install to the user site because it will "
                        "lack sys.path precedence to %s in %s" %
                        (existing_dist.project_name, existing_dist.location)
                    )
            else:
                self.conflicts_with = existing_dist
        return True

def was_installed_by_pip(pkg):
    # type: (str) -> bool
    """Checks whether pkg was installed by pip

    This is used not to display the upgrade message when pip is in fact
    installed by system package manager, such as dnf on Fedora.
    """
    try:
        dist = pkg_resources.get_distribution(pkg)
        return "pip" == get_installer(dist)
    except pkg_resources.DistributionNotFound:
        return False

def __init__(self, req, comes_from, source_dir=None, editable=False,
                 url=None, as_egg=False, update=True, prereleases=None,
                 editable_options=None, from_bundle=False, pycompile=True):
        self.extras = ()
        if isinstance(req, string_types):
            req = pkg_resources.Requirement.parse(req)
            self.extras = req.extras
        self.req = req
        self.comes_from = comes_from
        self.source_dir = source_dir
        self.editable = editable

        if editable_options is None:
            editable_options = {}

        self.editable_options = editable_options
        self.url = url
        self.as_egg = as_egg
        self._egg_info_path = None
        # This holds the pkg_resources.Distribution object if this requirement
        # is already available:
        self.satisfied_by = None

def was_installed_by_pip(pkg):
    """Checks whether pkg was installed by pip

    This is used not to display the upgrade message when pip is in fact
    installed by system package manager, such as dnf on Fedora.
    """
    try:
        dist = pkg_resources.get_distribution(pkg)
        return (dist.has_metadata('INSTALLER') and
                'pip' in dist.get_metadata_lines('INSTALLER'))
    except pkg_resources.DistributionNotFound:
        return False

self.conflicts_with appropriately."""

        if self.req is None:
            return False
        try:
            # DISTRIBUTE TO SETUPTOOLS UPGRADE HACK (1 of 3 parts)
            # if we've already set distribute as a conflict to setuptools
            # then this check has already run before.  we don't want it to
            # run again, and return False, since it would block the uninstall
            # TODO: remove this later
            if (self.req.project_name == 'setuptools'
                and self.conflicts_with
                and self.conflicts_with.project_name == 'distribute'):
                return True
            else:
                self.satisfied_by = pkg_resources.get_distribution(self.req)
        except pkg_resources.DistributionNotFound:
            return False
        except pkg_resources.VersionConflict:
            existing_dist = pkg_resources.get_distribution(self.req.project_name)
            if self.use_user_site:
                if dist_in_usersite(existing_dist):
                    self.conflicts_with = existing_dist
                elif running_under_virtualenv() and dist_in_site_packages(existing_dist):
                    raise InstallationError("Will not install to the user site because it will lack sys.path precedence to %s in %s"
                                            %(existing_dist.project_name, existing_dist.location))
            else:
                self.conflicts_with = existing_dist
        return True