docs: def get_edges(self):
          """
          Returns a list of tuples. Each tuple contains two elements (parent, child) for each edge.
  
          Examples
          --------
          >>> reader = XBNReader('xbn_test.xml')
          >>> reader.get_edges()
          [('a', 'b'), ('a', 'c'), ('b', 'd'), ('c', 'd'), ('c', 'e')]
          """
          return [(arc.get('PARENT'), arc.get('CHILD')) for arc in self.bnmodel.find('STRUCTURE')]