docs: def get_edges(self):
          """
          Returns the edges of the network
  
          Examples
          --------
          >>> reader = XMLBIF.XMLBIFReader("xmlbif_test.xml")
          >>> reader.get_edges()
          [['family-out', 'light-on'],
           ['family-out', 'dog-out'],
           ['bowel-problem', 'dog-out'],
           ['dog-out', 'hear-bark']]
          """
          edge_list = [[value, key] for key in self.variable_parents
                       for value in self.variable_parents[key]]
          return edge_list