字典数据类型内置方法

字典数据类型内置方法

1.作用

用于对值添加描述信息

2.定义方式

  #用{}以逗号隔开加入键值对key:value
  info_dict={'name':'bb','age':18,'height':180,'weight':140,'gender':'male','hobby_lsit':['13','666','233']}

3.内置方法

优先掌握

1.按key取值,即可取也可改变

info_dict = {'name': 'bb', 'age': 18, 'height': 180, 'weight': 140, 'gender': 'male', 'hobby_list': ['13', '666','233']}
print(info_dict['hobby_list'])
info_dict['age']=20
print(info_dict)

['13', '666', '233']

2.长度len

print(len(info_dict))

6

3.in/not in

print('name' in info_dict)

True

4.for循环

for i in info_dict:
    print(i)

name
age
height
weight
gender
hobby_list

5.键keys()、值values()、键值对items() items用得最多一般和解压缩一起用

print(list(info_dict.keys()))  # list
print(list(info_dict.values()))  # list
print(list(info_dict.items()))

['name', 'age', 'height', 'weight', 'gender', 'hobby_list']
['bb', 18, 180, 140, 'male', ['13', '666', '233']]
[('name', 'bb'), ('age', 18), ('height', 180), ('weight', 140), ('gender', 'male'), ('hobby_list', ['13', '666', '233'])]

6.循环

info_dict = {'name': 'bb', 'age': 18, 'height': 180, 'weight': 140, 'gender': 'male', 'hobby_lsit': ['13', '666','233']}
for i in info_dict.items():
    print(i)

for k, v in info_dict.items():
    print(k, v)
lt = [[1, 2, 3], [2, 3, 4], [5, 6, 7]]
for a, b, c in lt:
    print(a, b, c)

('name', 'bb')
('age', 18)
('height', 180)
('weight', 140)
('gender', 'male')
('hobby_lsit', ['13', '666', '233'])
name bb
age 18
height 180
weight 140
gender male
hobby_lsit ['13', '666', '233']
1 2 3
2 3 4
5 6 7

需要掌握

1.copy/pop/popitem/clear

info_dict = {'name': 'wangdapao', 'age': 18, 'height': 120, 'gender': 'female', 'hobby_list': ['dapao', '666', '233']}
print(info_dict.copy())

info_dict.pop('name')

print(info_dict)

info_dict.popitem()  # 早期的时候字典是无序的,是随机删除的,但是由于python3底层优化了字典,让字典看的貌似有序了,所以默认删除最后一个
print(info_dict)

info_dict.clear()
print(info_dict)

{'name': 'wangdapao', 'age': 18, 'height': 120, 'gender': 'female', 'hobby_list': ['dapao', '666', '233']}
{'age': 18, 'height': 120, 'gender': 'female', 'hobby_list': ['dapao', '666', '233']}
{'age': 18, 'height': 120, 'gender': 'female'}
{}

2.get

print(info_dict.get('age'))
# print(info_dict['name'])
print(info_dict.get('name', 'nick'))  # 如果有,就返回真正的值;如果没有,默认返回None,也可以指定返回

18
wangdapao

3.update

info_dict = {'name': 'wangdapao', 'age': 18, 'height': 120, 'gender': 'female', 'hobby_list': ['dapao', '666', '233']}

info_dict.update({'a':1})
print(info_dict)

{'name': 'wangdapao', 'age': 18, 'height': 120, 'gender': 'female', 'hobby_list': ['dapao', '666', '233'], 'a': 1}

4.fromkeys(快速生成字典)

print(dict.fromkeys(['a',2,3,4,5],'nick'))

5.setdefault

info_dict = {'name': 'wangdapao', 'age': 18, 'height': 120, 'gender': 'female', 'hobby_list': ['dapao', '666', '233']}

info_dict.setdefault('gender', 123123)  # 有则不变,无则往里面追加了值
print(info_dict)

{'name': 'wangdapao', 'age': 18, 'height': 120, 'gender': 'female', 'hobby_list': ['dapao', '666', '233']}

4.存在一个or多个值

多个值

5.有序or无序

无序

6.可变or不可变

可变

dic = {'a':1}
print(id(dic))
dic['b'] = 1
print(id(dic))

2575668575472
2575668575472