python 字典 update

# 数据
b = {1: {2: 2, 3: 3}}
c = {21: {2: 2, 3: 3}}
# 更新数据
d = b.update(c)
# 验证
print(b.update(c))
print(d)
print(b)

结果：

None
None
{1: {2: 2, 3: 3}, 21: {2: 2, 3: 3}}

 

从上可知update不反返回值