Python中dictl类型的update方法print为None

dict={"a":1,"b":2}
dict1={"b":3,"c":4}

result=dict.update(dict1)
print(dict)
print(result)

打印结果：
{"a":1,"b":3,"c":4}
NONE

result原因是update方法不会返回更新后的结果