<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def purge_obsolete_samples(self, config, now):
 """ Timeout any windows that have expired in the absence of any events """

        expire_age = config.samples * config.time_window_ms
        for sample in self._samples:
            if now - sample.last_window_ms >= expire_age:
                sample.reset(now)