cache.py 文件源码

def _get_candidates(self, link, package_name):
        can_not_cache = (
            not self.cache_dir or
            not package_name or
            not link
        )
        if can_not_cache:
            return []

        canonical_name = canonicalize_name(package_name)
        formats = index.fmt_ctl_formats(
            self.format_control, canonical_name
        )
        if not self.allowed_formats.intersection(formats):
            return []

        root = self.get_path_for_link(link)
        try:
            return os.listdir(root)
        except OSError as err:
            if err.errno in {errno.ENOENT, errno.ENOTDIR}:
                return []
            raise