code: def stack_type(self, stack_type):
          
          allowed_values = ["zero", "expand", "wiggle", "silhouette"]  # noqa: E501
          if stack_type not in allowed_values:
              raise ValueError(
                  "Invalid value for `stack_type` ({0}), must be one of {1}"  # noqa: E501
                  .format(stack_type, allowed_values)
              )
  
          self._stack_type = stack_type
docs: Sets the stack_type of this ChartSettings.
  
          Type of stacked chart (applicable only if chart type is stacked).  zero (default) means stacked from y=0.  expand means Normalized from 0 to 1.  wiggle means Minimize weighted changes. silhouette means to Center the Stream  # noqa: E501
  
          :param stack_type: The stack_type of this ChartSettings.  # noqa: E501
          :type: str