Python——字典及其特性，常用方法

字典是一个无序的数据集合
通常输出的顺序和定义的顺序不一致

users = ['user1','user2'] passwd = ['123','456'] print(zip(users,passwd)) print(list(zip(users,passwd))) #列表 print(dict(zip(users,passwd))) #字典

定义一个空字典

s = {} print(type(s))

字典：key-value键-值对
value可以是任意的数据类型

s = { 'westos':[11,22,33], 'mysql':[44,55,66] } print(s) print(type(s))

工厂函数

d = dict() print(type(d))

d = dict(a=1,b=2) print(d,type(d))

字典的嵌套

students = { '02165071':{ 'name':'zyw', 'age':'18' }, '02165070':{ 'name':'lhr', 'age':'19' } } print(students['02165071']['name'])

所有的key的value值相同

#所有的key的value值相同 print({}.fromkeys({'1','2'},'000000'))

字典，不支持索引和切片，但可通过key值查询values值，key值唯一

字典的重复和连接无意义
字典的key值是唯一的
成员操作符

d = { '1':'a', '2':'b' } print('1' in d)

for循环，默认遍历字典的key值

d = { '1':'a', '2':'b' } for key in d: print(key)

遍历字典

d = { '1':'a', '2':'b' } for key in d: print(key,d[key])

d = { '1':'a', '2':'b' } for k,v in d.items(): print(k,v)

如果key值存在，则更新对应的value值，如果key值不存在，则添加对应的key-value数值

service = { 'http':80, 'mysql':3306, 'smtp':25 } service['ftp'] = 21 print(service)

service = { 'http':80, 'mysql':3306, 'smtp':25 } service['ftp'] = 21 print(service) service['http'] = 443 print(service)

添加多个key-value值

service = { 'http':80, 'mysql':3306, 'smtp':25 } service_backup = { 'https':443, 'tomcat':8080, 'http':8080 } service.update(service_backup) #service变，service_backup不变 print(service)

service = { 'http':80, 'mysql':3306, 'smtp':25 } service_backup = { 'https':443, 'tomcat':8080, 'http':8080 } service.update(flask=9000,http=8000) print(service)

setdefault添加key值
如果key值存在，不做修改
如果key值不存在，添加对应的key-value

service = { 'http':80, 'mysql':3306, 'smtp':25 } service.setdefault('http',9000) print(service) service.setdefault('oracle',44575) print(service)

service = { 'http':80, 'mysql':3306, 'smtp':25 } del service['http'] print(service)

pop删除指定的key的key-value
如果key存在，删除，并返回删除key对应value
如果不存在，报错

service = { 'http':80, 'mysql':3306, 'smtp':25 } item = service.pop('http') print(item) print(service)

service = { 'http':80, 'mysql':3306, 'smtp':25 } item = service.pop('https') print(item) print(service)

popitem删除最后一个key-value值对

service = { 'http':80, 'mysql':3306, 'smtp':25 } item = service.popitem() print(service)

clear 清空字典内容

service = { 'http':80, 'mysql':3306, 'smtp':25 } service.clear() print(service)

print(services.keys())

service = { 'http':80, 'mysql':3306, 'smtp':25 } print(service.keys())

print(services.values())

service = { 'http':80, 'mysql':3306, 'smtp':25 } print(service.values())

print(services.items())

service = { 'http':80, 'mysql':3306, 'smtp':25 } print(service.items())

key不存在，默认返回None
key不存在，有default，则返回default值

service = { 'http':80, 'mysql':3306, 'smtp':25 } print(service.get('https'))

service = { 'http':80, 'mysql':3306, 'smtp':25 } for k in service: print(k,service[k])

如果key值存在，返回
如果不存在，默认返回None，如果需要指定返回值，传值即可

service = { 'http':80, 'mysql':3306, 'smtp':25 } print(service.get('https','key is not exit'))

数字重复统计:
1). 随机生成1000个整数;
2). 数字的范围[20, 100],
3). 升序输出所有不同的数字及其每个数字重复的次数;

import random all_num = [] for item in range(1000): all_num.append(random.randint(20,100)) print(all_num) sorted_num = sorted(all_num) num_dict = {} for num in sorted_num: if num in num_dict: num_dict[num] += 1 else: num_dict[num] = 1 print(num_dict)

输入一串字符串，统计每个单词出现的次数
例如：
‘westos hello python westos’
westos 2
hello 1
python 1

思路：
1.把该字符串分割处理，以空格为分隔符
2.定义一个空字典，用字典存储该单词和他出现的次数
3.依次遍历循环列表，如果列表元素不再字典的key中，将元素key的value值为1，如果列表的元素在字典的key中，直接更新该key对应的value值，在原有的基础上加1

str = input('请输入: ') str_list = str.split() print(str_list) dict = {} for item in str_list: if item not in dict: dict[item] = 1 else: dict[item] += 1 print(dict)