code: def extend(self, other):
  		
  		for key, value in other.iteritems():
  			if key not in self:
  				self[key] = _shallowcopy(value)
  			else:
  				self[key].extend(value)
docs: Appends the segmentlists from other to the corresponding
  		segmentlists in self, adding new segmentslists to self as
  		needed.