python基础2--字典

字典

字典的每个键值(key=>value)对用冒号(:)分割，每个对之间用逗号(,)分割，整个字典包括在花括号({})中

语法：

1 goods = {
2     ‘apple‘:4.5,
3     ‘orange‘:2.3,
4     ‘banana‘:3.5
5      }

字典的特性：

• dict是无序的
• key必须是唯一的

1 >>> goods
2 {‘apple‘: 4.5, ‘banana‘: 3.5, ‘orange‘: 2.3}
3 >>> goods[‘peach‘]=5.0
4 >>> goods
5 {‘apple‘: 4.5, ‘banana‘: 3.5, ‘orange‘: 2.3, ‘peach‘: 5.0}

2.修改

1 >>> goods[‘apple‘]=5.5  # 将苹果的价格改为 5.5
2 >>> goods
3 {‘apple‘: 5.5, ‘banana‘: 3.5, ‘orange‘: 2.3, ‘peach‘: 5.0}

3.删除元素

 1 >>> goods
 2 {‘apple‘: 5.5, ‘banana‘: 3.5, ‘orange‘: 2.3, ‘peach‘: 5.0}
 3 >>> goods.pop(‘peach‘)    #删除最后一个，并返回value的值
 4 5.0
 5 >>> goods
 6 {‘apple‘: 5.5, ‘banana‘: 3.5, ‘orange‘: 2.3}
 7
 8 >>> del goods[‘banana‘]   # 指定 key的删除
 9 >>> goods
10 {‘apple‘: 5.5, ‘orange‘: 2.3}
11
12 >>> goods
13 {‘apple‘: 5.5, ‘grape‘: 6.0, ‘orange‘: 2.3, ‘watermelon‘: 12.0}
14 >>> goods.popitem()   # 随机删除
15 (‘apple‘, 5.5)
16 >>> goods
17 {‘grape‘: 6.0, ‘orange‘: 2.3, ‘watermelon‘: 12.0}

4.查找

 1 >>> goods
 2 {‘grape‘: 6.0, ‘orange‘: 2.3, ‘watermelon‘: 12.0}
 3 >>> ‘grape‘ in goods
 4 True
 5 >>> goods.get(‘orange‘)    # 知道key,获取 value
 6 2.3
 7 >>> goods[‘watermelon‘]
 8 12.0
 9 >>> goods[‘apple‘]   # 如果一个key不存在,就会报错，get不会，不存在只会返回None
10 Traceback (most recent call last):
11   File "<stdin>", line 1, in <module>
12 KeyError: ‘apple‘

5.多级字典及操作

 1 area = {‘浙江‘:
 2             {
 3              ‘杭州‘:[‘西湖区‘,‘下城区‘,‘萧山区‘],
 4              ‘嘉兴‘:[‘南湖区‘,‘秀洲区‘,‘平湖市‘],
 5              ‘温州‘:[‘九湾区‘,‘鹿城区‘,‘洞头区‘]
 6              },
 7         ‘江苏‘:
 8             {
 9              ‘南京‘:[‘鼓楼区‘,‘玄武区‘,‘秦淮区‘],
10              ‘苏州‘:[‘姑苏区‘,‘吴中区‘,‘虎丘区‘],
11              ‘常州‘:[‘武进区‘,‘金坛市‘,‘溧阳市‘]
12             }
13
14
15         }
16
17 >>> area[‘浙江‘][‘杭州‘]
18 [‘西湖区‘, ‘下城区‘, ‘萧山区‘]
19
20
21 >>> area[‘浙江‘][‘杭州‘][1] += ‘,很大‘
22 >>> area[‘浙江‘][‘杭州‘]
23 [‘西湖区‘, ‘下城区,很大‘, ‘萧山区‘]

6.其他用法

 1 >>> area.keys()
 2 dict_keys([‘浙江‘, ‘江苏‘])
 3 >>> goods.values()
 4 dict_values([6.0, 2.3, 12.0])
 5 >>> goods.keys()
 6 dict_keys([‘grape‘, ‘orange‘, ‘watermelon‘])
 7
 8 {‘grape‘: 6.0, ‘orange‘: 2.3, ‘watermelon‘: 12.0}
 9 >>> b = {1:2,3:4,‘grape‘:4.5}
10 >>> goods.update(b)
11 >>> goods
12 {1: 2, 3: 4, ‘grape‘: 4.5, ‘orange‘: 2.3, ‘watermelon‘: 12.0}
13
14 >>> goods.items()
15 dict_items([(1, 2), (3, 4), (‘grape‘, 4.5), (‘orange‘, 2.3), (‘watermelon‘, 12.0)])

7.遍历字典

1 for key in goods:
2     print(key,goods[key])
3 #或
4 for k,v in goods.items():
5     print(k,v)