code: def add_fields(self, fields):
          
          if isinstance(fields, string_types):
              fields = [fields]
          elif type(fields) is tuple:
              fields = list(fields)
  
          field_objects = [self.add_field(field) for field in fields]
          return field_objects
docs: Adds all of the passed fields to the table's current field list
  
          :param fields: The fields to select from ``table``. This can be
              a single field, a tuple of fields, or a list of fields. Each field can be a string
              or ``Field`` instance
          :type fields: str or tuple or list of str or list of Field or :class:`Field <querybuilder.fields.Field>`