code: def _process_facet_field_spies(self, spies):
          
          facet_dict = {}
          for spy in spies:
              field = self.schema[spy.slot]
              field_name, field_type = field['field_name'], field['type']
  
              facet_dict[field_name] = []
              for facet in list(spy.values()):
                  if field_type == 'float':
                      # the float term is a Xapian serialized object, which is
                      # in bytes.
                      term = facet.term
                  else:
                      term = facet.term.decode('utf-8')
  
                  facet_dict[field_name].append((_from_xapian_value(term, field_type),
                                                 facet.termfreq))
          return facet_dict
docs: Returns a dict of facet names with lists of
          tuples of the form (term, term_frequency)
          from a list of spies that observed the enquire.