add and del from graph

import functools

g = {1:{2,3,4}, 2:{1,3}, 3:{1,4}, 4:{1,3}}
lst = [(2,4), (3,2)]

def addToGraph(graph, lst):

    def reducer(acc, elem):
        graph[elem[0]].add(elem[1])
        #graph[elem[1]].add(elem[0])

    functools.reduce(reducer, lst, None)
    return graph

def delFromGraph(graph, lst):
    def reducer(acc, elem):
        graph[elem[0]].discard(elem[1])
        #graph[elem[1]].discard(elem[0])
    functools.reduce(reducer, lst, None)
    return graph

print(addToGraph(g, lst))
print(delFromGraph(g, [(2,1), (3,1)]))