code: def add_show_function(self, show_name, show_func):
          
          if self.get_show_function(show_name) is not None:
              raise CloudantArgumentError(110, show_name)
  
          self.shows.__setitem__(show_name, show_func)
docs: Appends a show function to the locally cached DesignDocument
          shows dictionary.
  
          :param show_name: Name used to identify the show function.
          :param show_func: Javascript show function.