Python基础之while和for

实现ATM的输入密码重新输入的功能

while True:
user_db = 'nick'
pwd_db = '123'

inp_user = input('username: ')
inp_pwd = input('password: ')
if inp_user == user_db and pwd_db == inp_pwd:
    print('login successful')
else:
    print('username or password error')

while + break 组合

while True:
user_db = 'nick'
pwd_db = '123'

inp_user = input('username:')
inp_pwd = input('password:')
if inp_user == user_db and pwd_db == inp_pwd:
    print('login successful')
    break
else:
    print('username or password error')

print('退出了while循环')

while + continue (continue的意思是终止本次循环，直接进入下一次循环)

n = 1
while n<10:
if n == 8:
continue
print(n)
n += 1

while 循环的嵌套

退出内层循环的while循环嵌套

while True:
user_db = 'nick'
pwd_db = '123'

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(f'{cmd} 请输入你需要执行的命令：')
        if cmd == 'q':
            break
        print(f'{cmd} 功能执行')
    else:
        print('username or password error')

print(' 退出了while循环 ')

退出了双层循环的while循环嵌套

while True:
user_db = 'nick'
pwd_db = '123'

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(f'{cmd} 功能执行')
    break
else:
    print('username or password error')

print('退出了while循环')

tag键控制循环退出

tag = True
while tag:
user_db = 'nick'
pwd_db = '123'

inp_user = input('username:')
inp_pwd = input('password:')

if inp_user == user_db and pwd_db == inp_pwd:
    print("login successful ")

    while tag:
        cmd = input('  请输入你需要的命令：')
        if cmd == 'q':
            tag = False
        print(f'{cmd} 功能执行')
else:
    print('退出了while循环')

print('退出了while循环')

# while+else
n = 1
while n < 3:
    print(n)
    n += 1
else:
    print('else会在while没有被break时才会执行else中的代码'
    
'''
1
2
else会在while没有被break时才会执行else中的代码
'''

# for循环
info = {'name': 'nick', 'age': 19}

for item in info:
    # 取出info的keys
    print(item)
'''
name
age
'''

name_list = ['nick', 'jason', 'tank', 'sean']
for item in name_list:
    print(item)
"""
nick
jason
tank
sean
"""

# for循环按照索引取值
name_list = ['nick', 'jason', 'tank', 'sean']
# for i in range(5): # 5是数的用法
# for i in range(1, 10): # range顾头不顾尾
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)
"""
nick
tank
sean
"""

# for 循环嵌套
for i in range(3):
    print(f'-----:{i}')
    for j in range(2):
        print(f'******:{j}')

"""
-----:0
*****:0
*****:1
-----:1
*****:0
*****:1
-----:2
*****:0
*****:1
"""

# for+else
name_list = ['nick', 'jason', 'tank', 'sean']
for name in name_list:
    print(name)
else:
    print('for循环没有被break中断掉')
'''
nick
jason
tank
sean
for循环没有break中断掉
'''

#for 循环实现loading(pycharm中里有优化机制，效果展现不出来，需在jupyter中运行)
import time

print('Loading', end='')
for i in range(6):
    print(".", end='')
    time.sleep(0.2)