def cull_to_timestep(self, timestep=<NUM_LIT:1>):
valid_s = self.header.analysis_period.VALIDTIMESTEPS.keys()<EOL>assert timestep in valid_s,'<STR_LIT>'.format(timestep, valid_s)<EOL>new_ap, new_values, new_datetimes = self._timestep_cull(timestep)<EOL>new_header = self.header.duplicate()<EOL>new_header._analysis_period = new_ap<EOL>new_coll = HourlyDiscontinuousCollection(<EOL>new_header, new_values, new_datetimes)<EOL>new_coll._validated_a_period = True<EOL>return new_coll<EOL>
Get a collection with only datetimes that fit a timestep.