code: def add_field(self, name, label, field_type, *args, **kwargs):
          
          if name in self._dyn_fields:
              raise AttributeError('Field already added to the form.')
          else:
              self._dyn_fields[name] = {'label': label, 'type': field_type,
                                        'args': args, 'kwargs': kwargs}
docs: Add the field to the internal configuration dictionary.