Python for while循环

一. while 循环

while_stmt ::=  "while" assignment_expression ":" suite
                ["else" ":" suite]
while 条件:
    条件满足时，执行语句

1. 1~100求和运算

i = 0
r = 0
while i <= 100:
    r += i
    i += 1
print('1+2+3+...+100 = %d' % r) # 5050,计算1~100求和

我们可以通过设置条件表达式永远不为 false 来实现无限循环，实例如下：

2. while 无限循环

while True:
    print("hello,21yi.com") # CTRL+C退出循环

# 无限循环实现简单的密码验证
while True:
    password = input('请输入您的密码：')
    if "21yi.com" == password:
        print('密码正确')
        break
    else:
        print('密码错误')
        continue

使用 CTRL+C 来退出当前的无限循环。

无限循环在服务器上客户端的实时请求非常有用。

3. while 嵌套

类似if语句，while也支持嵌套，如嵌套实现9x9乘法表：

level = 1
while level <= 9:
    init = 1
    while init <= level:
        print('%d x %d = %d\t' % (level, init, init * level), end='')
        init += 1
    print('\r')
    level += 1

# 1 x 1 = 1
# 2 x 1 = 2  2 x 2 = 4
# 3 x 1 = 3  3 x 2 = 6  3 x 3 = 9
# 4 x 1 = 4  4 x 2 = 8  4 x 3 = 12 4 x 4 = 16
# 5 x 1 = 5  5 x 2 = 10 5 x 3 = 15 5 x 4 = 20 5 x 5 = 25
# 6 x 1 = 6  6 x 2 = 12 6 x 3 = 18 6 x 4 = 24 6 x 5 = 30 6 x 6 = 36
# 7 x 1 = 7  7 x 2 = 14 7 x 3 = 21 7 x 4 = 28 7 x 5 = 35 7 x 6 = 42 7 x 7 = 49
# 8 x 1 = 8  8 x 2 = 16 8 x 3 = 24 8 x 4 = 32 8 x 5 = 40 8 x 6 = 48 8 x 7 = 56 8 x 8 = 64
# 9 x 1 = 9  9 x 2 = 18 9 x 3 = 27 9 x 4 = 36 9 x 5 = 45 9 x 6 = 54 9 x 7 = 63 9 x 8 = 72 9 x 9 = 81

二. for 循环语句

Python for循环可以遍历如（字符串、元组、列表）等其他可遍历的对象

for_stmt ::=  "for" target_list "in" expression_list ":" suite
              ["else" ":" suite]

# 数字List
for i in range(1, 6):  # [1,2,3,4,5]
    print(i)  # 1 2 3 4 5
# 字符串
for i in "21yi.com":
    print(i)