'Return modification time of cache file, or 0 if it does not exist.
Time is in units returned by os.stat in the mtime field, which is
platform-dependent.'

def mtime(self, key):

    if (not self.init_entry(key)):
        return 0
    else:
        sinfo = os.stat(self.cache_path(key))
        return sinfo.st_mtime
