python 字典的遍历以及用sorted内置函数对其排序

mapping1 = {"a":"234", "b":"12", "c":"45556"}
for i,v in mapping1.items():
　　print(i,v)
print("&"*20)

for i in mapping1:
　　print(i)
print("&"*20)

for i in mapping1.items():
　　print(i)
print("&"*20)

tmp = sorted(mapping1, key = lambda x: len(x), reverse = False)