code: def get_sigmasqs(self, instruments=None):
  		
  		if len(self):
  			if not instruments:
  				instruments = map(str, \
  					instrument_set_from_ifos(self[0].ifos))
  			return dict((ifo, self.get_sigmasq(ifo))\
  				    for ifo in instruments)
  		else:
  			return dict()
docs: Return dictionary of single-detector sigmas for each row in the
  		table.