1.统计字符

统计字符串中每个字符出现的次数

s = 'l like summer very much'
#去掉空格
s = s.replace(" ","")
d = dict()
for i in s:if i in d:d[i] += 1else:d[i] = 1
for i in d:print(i,d[i])

2.求不重复的随机数

#导入随机数
import random
a = int(input("请输入随机数的范围："))
n = int(input("请输入随机数的个数："))
s = set()
while len(s) < n :i = random.randint(1,a)s.add(i)
print(s)

3.设计不可变集合

set    可变集合   

可读可写的集合

基本功能：关系检测和元素去重

frozenset   不可变集合

只读的set集合

基本功能：定义哈希值

将两个城市定为键，将城市距离定义为值

city_discance = {}
key1 = frozenset(["Beijing","Tianjing"])
key2 = frozenset(["Shanghai","Zhejinag"])
key3 = frozenset(["Chongqing","Chengdu"])
city_discance[key1] = 123
city_discance[key2] = 456
city_discance[key3] = 789
print(city_discance)

4.创建用户登录系统

#统计用户名和密码
user = {}
#统计输入密码的次数为3
count = 3
while True:print("*"*40)name = input("请输入用户名：")if name in user:while count >= 0:pw = input("请输入密码：")if user[name] == pw:print("密码正确，登录成功！")breakelse:print("登录失败，你还有%d次机会"%count)count -= 1else:print("密码输入次数已到")else:f = input("用户名不存在，是否创建用户名[y/n]")if f == "y":while True:name = input("请输入用户名： ")if name in user:print("用户名已存在")else:pw = input("请输入密码：")repw = input("请再次输入密码")if pw == repw:user[name] =1 pwprint("用户创建成功")breakelse:print("密码输入有误")else:print("退出系统，欢迎下次再来")