python第八课

字典

info = {"k1":"v1", "k2":"v2"}
字典里面保存了两个值，每一个都是键值对。

info = {"k1": 18, "k2": True, 1:"asdf",

"k3": [11, 22, 33, {"kk1": "vv1", "kk2": "vv2", "kk3": (11, 22)}], "k4": (11, 22, 33)}

字典的value可以是任意值，列表不能作为字典的key，元组可以，布尔值可以作为字典的key，但作为key时会和1、0冲突，字典也不能作为字典的key，会报错nohashable。

info = {0: "11", True: "234", (1, 2): "star",}
print(info)
{0: '11', True: '234', (1, 2): 'star'}

info = {1: "11", True: "234", (1, 2): "star",}
print(info)
{1: '234', (1, 2): 'star'}

 

python3.6以前的字典是无序的，以后的都是改写了算法，是有序的了。

字典的索引，用dict["key"]

info = {"k1": 18, 2: True, "k3": [11, 22, 33, {"kk1": "vv1", "kk2": "vv2", "kk3": (11, 22)}], "k4": (11, 22, 33)}
print(info["k3"][3]["kk3"][0])

删除操作

del dict["key"]

for 循环

默认循环所有的key

info = {"k1": 18, 2: True, "k3": [11, 22, 33, {"kk1": "vv1", "kk2": "vv2", "kk3": (11, 22)}], "k4": (11, 22, 33)}

for item in info.keys():
    print(item)

for k, v in info.items():
    print(k, v)

方法

clear

copy

fromkeys
循环可迭代对象创建给予的key生成字典
v = dict.fromkeys(["k1","k2","k3"],123)
->{'k1': 123, 'k2': 123, 'k3': 123}

get

x = v.get('k1', 121)
print(x)

pop

x = v.pop('k1')
print(v)

　x = v.pop('k', 90)
　print(v, x)

popitem

x = v.popitem()
print(v)

默认删除最后一个，因为3.6以后字典有序

setdefult

x = v.setdefault('k1', '122')
print(v, x)
-》{'k1': 123, 'k2': 123} 123

x = v.setdefault('k3', '122')
print(v, x)

-》{'k1': 123, 'k2': 123, 'k3': '122'} 122

如果不存在设置的值，则增加一项键值对。

update

v.update(k1=120, k2=121,k4=233)
print(v)
-》{'k1': 120, 'k2': 121, 'k3': '122', 'k4': 233}

常用：keys()  values()  items()  get()  update()