code: def apply_iter(cls, rows, mapping, resolver, scope=None):
          
          mapper = cls(mapping, resolver, scope=scope)
          for row in rows:
              _, data = mapper.apply(row)
              yield data
docs: Given an iterable ``rows`` that yield data records, and a
          ``mapping`` which is to be applied to them, return a tuple of
          ``data`` (the generated object graph) and ``err``, a validation
          exception if the resulting data did not match the expected schema.