python遍历字典一共有四种方式
D={‘a’：1，‘b’：2，’b‘：3，’d‘：4}
1. 遍历key值
for key in a:
pritn(key+':'+a[key])
for key in a.keys():
print(key+':'+a[key])
2.遍历value值
for value in a.values():
print(value)
3.遍历字典项
for kv in a.items():
print(kv)
（‘a’,'1'）(...)
4.遍历字典键值
for key,value in a.items():
print(key+':'+value)
for (key,value) in a.items():
print(key+':'+value)