python 流程控制

if
cls = ‘human‘
gender = ‘female‘
age = 24

if cls == ‘human‘ and gender == ‘female‘ and age > 28 and age :
    print(‘开始表白‘)

print(‘end...‘)

if...else
cls = ‘human‘
gender = ‘female‘
age = 38

if cls == ‘human‘ and gender == ‘female‘ and age > 16 and age :
    print(‘开始表白‘)
else:
    print(‘阿姨好‘)

 if...elif...else
cls = ‘human‘
gender = ‘female‘
age = 28

if cls == ‘human‘ and gender == ‘female‘ and age > 16 and age :
    print(‘开始表白‘)
elif cls == ‘human‘ and gender == ‘female‘ and age > 22 and age :
    print(‘考虑下‘)
else:
    print(‘阿姨好‘)

# # -*-coding:utf-8-*-
# 如果 成绩>=90，打印"优秀"
# * 如果 成绩>=80 并且 成绩
# * 如果 成绩>=70 并且 成绩
# # * 其他情况：打印"差"

score = input("请输入你的成绩：")
score = int(score)

if score >= 90:
    print ("优秀")
elif score >= 80:
    print ("良好")
elif score >= 70:
    print  ("普通")
else:
    print ("差")

ser_from_db = ‘jason‘
pwd_from_db = ‘123‘

user_from_inp = input(‘username: ‘)
pwd_from_inp = input(‘password: ‘)


if user_from_inp == user_from_db and pwd_from_inp == pwd_from_db:
    print (‘登陆成功‘)
else:
    print (‘用户名或密码错误‘)

退出内层循环的while循环嵌套
user_db = ‘jason‘
pwd_db = ‘123‘
while True:
    inp_user = input(‘username: ‘)
    inp_pwd = input(‘password: ‘)
    if inp_user == user_db and pwd_db == inp_pwd:
        print(‘login successful‘)
        while True:
            cmd = input(‘请输入你需要的命令：‘)
            if cmd == ‘q‘:
                break
            print(‘%s功能执行‘%cmd)
    else:
        print(‘username or password error‘)
print(‘退出了while循环‘)

退出内层循环的while循环嵌套
user_db = ‘jason‘
pwd_db = ‘123‘
while True:
    inp_user = input(‘username: ‘)
    inp_pwd = input(‘password: ‘)
    if inp_user == user_db and pwd_db == inp_pwd:
        print(‘login successful‘)
        while True:
            cmd = input(‘请输入你需要的命令：‘)
            if cmd == ‘q‘:
                break
            print(‘%s功能执行‘%cmd)
    else:
        print(‘username or password error‘)
print(‘退出了while循环‘)

# 退出双层循环的while循环嵌套
user_db = ‘jason‘
pwd_db = ‘123‘
flag = True
while flag:
    inp_user = input(‘username: ‘)
    inp_pwd = input(‘password: ‘)
    if inp_user == user_db and pwd_db == inp_pwd:
        print(‘login successful‘)
        while flag:
            cmd = input(‘请输入你需要的命令：‘)
            if cmd == ‘q‘:
                flag = False
                break
            print(‘%s功能执行‘%cmd)
    else:
        print(‘username or password error‘)
print(‘退出了while循环‘)

# while+else
n = 1
while n :
      if n == 2:break  # 不会走else
    print(n)
    n += 1
else:
    print(‘else会在while没有被break时才会执行else中的代码‘)
```

or name in name_list:
  print(name)  # 对比与while更加简便

# 再来看for循环字典会得到什么
info = {‘name‘: ‘jason‘, ‘age‘: 19}
for item in info:
    print(item)  # 拿到字典所有的key
    print(info[item])
    
# for可以不依赖于索引取指，是一种通用的循环取指方式
# for的循环次数是由被循环对象包含值的个数决定的，而while的循环次数是由条件决定的

for i in range(1, 10):  # range顾头不顾尾
    print(i)

# python2与python3中range的区别(cmd窗口演示即可)

# for循环按照索引取值
name_list =  [‘jason‘, ‘nick‘, ‘tank‘, ‘sean‘]
# for i in range(0,5):  # 5是数的
for i in range(len(name_list)):
    print(i, name_list[i])

# for+break
name_list = [‘nick‘, ‘jason‘, ‘tank‘, ‘sean‘]
for name in name_list:
    if name == ‘jason‘:
        break
    print(name)

# for+continue
name_list = [‘nick‘, ‘jason‘, ‘tank‘, ‘sean‘]
for name in name_list:
    if name == ‘jason‘:
        continue
    print(name)

# 1.打印99乘法口诀表
‘‘‘
1*1=1
2*1=2 2*2=4
3*1=3 3*2=6 3*3=9
...
9*1=9.................9*9=81
‘‘‘
for i in range(1,10): #i=3
     for j in range(1,i+1):
         print(‘%s*%s=%s ‘ %(i,j,i*j),end=‘‘) #i=2 j=2
     print()