字典
2.1 字典的格式
格式
变量名={key1:value,key2:value,,,}
案例
info = {"name":"anfly","age":12,"sex":"男"}
字典的每个元素由2部分组成，键（key）:值（value）
2.2 根据键访问值
案例:有对应key的
info = {"name":"anfly","age":18,"sex":"男"}
print(info["name"])
案例:无对应key的
info = {"name":"anfly","age":12,"sex":"男"}
print(info["name12"])
思考:假如我们不确定字典中是否存在某个键而又想获取其值时,如何操作？
案例：有对应key的
info = {"name":"anfly","age":12,"sex":"男"}
print(info.get("name"))
案例:无对应key的
info = {"name":"anfly","age":12,"sex":"男"}
print(info.get("name"))
案例:无对应key的,默认返回数据
info = {"name":"anfly","age":12,"sex":"男"}
print(info.get("name12","无数据"))
无数据
2.3 修改元素
字典的每个元素中的数据是可以修改的，只要通过key找到，即可修改,否则是新增
案例:对应的key
info = {"name":"anfly","age":12,"sex":"男"}
info["age"] =14
print(info)
{'name': 'anfly', 'age': 14, 'sex': '男'}
案例：无对应的key
info = {"name":"anfly","age":12,"sex":"男"}
info["gender"] ="属鸡"
print(info)
{'name': 'anfly', 'age': 12, 'sex': '男', 'gender': '属鸡'}
总结
有对应的key则是修改数据，没有对应的key是新增数据
2.4 添加元素
案例：
info = {"name":"anfly","age":12,"sex":"男"}
info["gender"] ="属鸡"
print(info)
{'name': 'anfly', 'age': 12, 'sex': '男', 'gender': '属鸡'}
2.5 删除元素
del,clear() ---- 清空
2.5.1 del (删除指定的元素)
案例：删除整个字典
info = {"name":"anfly","age":12,"sex":"男"}
del info
print(info)
NameError: name 'info' is not defined
案例：删除某个元素
info = {"name":"anfly","age":12,"sex":"男"}
del info["name"]
print(info)
{'age': 12, 'sex': '男'}
2.5.2 clear清空
案例：
info = {"name":"anfly","age":12,"sex":"男"}
info.clear()
print(info)
{}
2.6 查询长度
len():查询键值对的个数
案例
info = {"name":"anfly","age":12,"sex":"男"}
print(len(info))
3
2.7 字典中循环
案例:取出字典中的key
info = {"name":"anfly","age":12,"sex":"男"}
for i in info.keys():
print(i)
结果:name age sex
案例:取出字典中的value
info = {"name":"anfly","age":12,"sex":"男"}
for i in info.values():
print(i)
结果:anfly 12 男
取出字典中的key和value
方式一：
info = {"name":"anfly","age":12,"sex":"男"}
for i in info.keys():
print(i,info[i])
方式二：
info = {"name":"anfly","age":12,"sex":"男"}
for k,v in info.items():
print(k,v)
扩充
如何实现带下标索引的遍历？
for i in 可迭代:
print(i)
enumerate()实现索引的遍历
names=["anfly","tom","Meachal"]
for i,chr in enumerate(names):
print(i,chr)
返回值
0 anfly
1 tom
2 Meachal
