code: def delete_edge(self, ind_node, dep_node):
          
          graph = self.graph
          if dep_node not in graph.get(ind_node, []):
              raise KeyError(
                  "No edge exists between %s and %s." % (ind_node, dep_node)
              )
          graph[ind_node].remove(dep_node)
docs: Delete an edge from the graph.
  
          Args:
              ind_node (str): The independent node to delete an edge from.
              dep_node (str): The dependent node that has a dependency on the
                              ind_node.
  
          Raises:
              KeyError: Raised when the edge doesn't already exist.