class order1():
    
  def _GetOrderBy(self):
    if 'orderby' in self.keys():
      return self['orderby']
    else:
      return None

  def _SetOrderBy(self, val):
    if val is not 'lastmodified' and val is not 'starttime':
      raise Error, "Order By must be either 'lastmodified' or 'starttime'"
    self['orderby'] = val

  orderby = property(_GetOrderBy, _SetOrderBy, 
      doc="""The orderby query parameter""")

class order2(dict):
    
  def _GetOrderBy(self):
    if 'orderby' in self.keys():
      return self['orderby']
    else:
      return None

  def _SetOrderBy(self, val):
    if val is not 'lastmodified' and val is not 'starttime':
      raise Error, "Order By must be either 'lastmodified' or 'starttime'"
    self['orderby'] = val

  orderby = property(_GetOrderBy, _SetOrderBy, 
      doc="""The orderby query parameter""")


o1 = order1()
o1.orderby = 'abc'

print o1.orderby

o2 = order2()
o2.orderby = 'abc'

print 'never go here'