def getLog(self, identifier):
        """Given a unix time, return a LogReader for an old log file."""
        if self.toDate(identifier) == self.lastDate:
            return self.getCurrentLog()
        filename = "%s.%s" % (self.path, self.suffix(identifier))
        if not os.path.exists(filename):
            raise ValueError("no such logfile exists")
        return LogReader(filename)
Given a unix time, return a LogReader for an old log file.
stackoverflow/venv/lib/python3.6/site-packages/twisted/python/logfile.py