<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _influxdb_url(self):
 """ Return REST API URL to access time series. """

        url = "{0}/db/{1}/series".format(self.influxdb.url.rstrip('/'), self.config.dbname)

        if self.influxdb.user and self.influxdb.password:
            url += "?u={0}&p={1}".format(self.influxdb.user, self.influxdb.password)

        return url