docstr: A proxy-call to the dataframe's `.sum()`.
code: def sum(self):
      """
      A proxy-call to the dataframe's `.sum()`.
      """
      return self.dataframe.sum()
  
imports: from abc import ABC
label_desc: Use image node_id 35 for calling the DataframeAbstract obj's underlying member method code with example usage: obj.sum() and returns: self