<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def iter_network_events(self, number=-1, etag=None):
 """Iterates over events on a network of repositories. :param int number: (optional), number of events to return. Default: -1 returns all available events :param str etag: (optional), ETag from a previous request to the same endpoint :returns: generator of :class:`Event <github3.events.Event>`\ s """

        base = self._api.replace('repos', 'networks', 1)
        url = self._build_url('events', base_url=base)
        return self._iter(int(number), url, Event, etag)