'Find an installed distribution that satisfies or conflicts
with this requirement, and set self.satisfied_by or
self.conflicts_with appropriately.'

def check_if_exists(self):

    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:
        self.conflicts_with = pkg_resources.get_distribution(self.req.project_name)
    return True
