code: def _attach_fields(obj):
      
      for attr in base_fields.__all__:
          if not hasattr(obj, attr):
              setattr(obj, attr, getattr(base_fields, attr))
      for attr in fields.__all__:
          setattr(obj, attr, getattr(fields, attr))
docs: Attach all the marshmallow fields classes to ``obj``, including
      Flask-Marshmallow's custom fields.