Return the time_slide_id corresponding to the offset vector
		described by offsetdict, a dictionary of instrument/offset
		pairs.

		If the optional create_new argument is None (the default),
		then the table must contain a matching offset vector.  The
		return value is the ID of that vector.  If the table does
		not contain a matching offset vector then KeyError is
		raised.

		If the optional create_new argument is set to a Process
		object (or any other object with a process_id attribute),
		then if the table does not contain a matching offset vector
		a new one will be added to the table and marked as having
		been created by the given process.  The return value is the
		ID of the (possibly newly created) matching offset vector.

		If the optional superset_ok argument is False (the default)
		then an offset vector in the table is considered to "match"
		the requested offset vector only if they contain the exact
		same set of instruments.  If the superset_ok argument is
		True, then an offset vector in the table is considered to
		match the requested offset vector as long as it provides
		the same offsets for the same instruments as the requested
		vector, even if it provides offsets for other instruments
		as well.

		More than one offset vector in the table might match the
		requested vector.  If the optional nonunique_ok argument is
		False (the default), then KeyError will be raised if more
		than one offset vector in the table is found to match the
		requested vector.  If the optional nonunique_ok is True
		then the return value is the ID of one of the matching
		offset vectors selected at random.

def get_time_slide_id(self, offsetdict, create_new = None, superset_ok = False, nonunique_ok = False):
		"""
		Return the time_slide_id corresponding to the offset vector
		described by offsetdict, a dictionary of instrument/offset
		pairs.

		If the optional create_new argument is None (the default),
		then the table must contain a matching offset vector.  The
		return value is the ID of that vector.  If the table does
		not contain a matching offset vector then KeyError is
		raised.

		If the optional create_new argument is set to a Process
		object (or any other object with a process_id attribute),
		then if the table does not contain a matching offset vector
		a new one will be added to the table and marked as having
		been created by the given process.  The return value is the
		ID of the (possibly newly created) matching offset vector.

		If the optional superset_ok argument is False (the default)
		then an offset vector in the table is considered to "match"
		the requested offset vector only if they contain the exact
		same set of instruments.  If the superset_ok argument is
		True, then an offset vector in the table is considered to
		match the requested offset vector as long as it provides
		the same offsets for the same instruments as the requested
		vector, even if it provides offsets for other instruments
		as well.

		More than one offset vector in the table might match the
		requested vector.  If the optional nonunique_ok argument is
		False (the default), then KeyError will be raised if more
		than one offset vector in the table is found to match the
		requested vector.  If the optional nonunique_ok is True
		then the return value is the ID of one of the matching
		offset vectors selected at random.
		"""
		# look for matching offset vectors
		if superset_ok:
			ids = [id for id, slide in self.as_dict().items() if offsetdict == dict((instrument, offset) for instrument, offset in slide.items() if instrument in offsetdict)]
		else:
			ids = [id for id, slide in self.as_dict().items() if offsetdict == slide]
		if len(ids) > 1:
			# found more than one
			if nonunique_ok:
				# and that's OK
				return ids[0]
			# and that's not OK
			raise KeyError("%s not unique" % repr(offsetdict))
		if len(ids) == 1:
			# found one
			return ids[0]
		# offset vector not found in table
		if create_new is None:
			# and that's not OK
			raise KeyError("%s not found" % repr(offsetdict))
		# that's OK, create new vector, return its ID
		return self.append_offsetvector(offsetdict, create_new)