code: def validate_attr(self, append):
          
          if append:
              existing_fields = getattr(self.attrs, self.kind_attr, None)
              if (existing_fields is not None and
                      existing_fields != list(self.values)):
                  raise ValueError("appended items do not match existing items"
                                   " in table!")
  
              existing_dtype = getattr(self.attrs, self.dtype_attr, None)
              if (existing_dtype is not None and
                      existing_dtype != self.dtype):
                  raise ValueError("appended items dtype do not match existing "
                                   "items dtype in table!")
docs: validate that we have the same order as the existing & same dtype