While循环

for循环用于针对集合中的每个元素都执行一个代码段。
while循环则不断地运行，一直到指定的条件不满足为止。

1 while 语法

while active_condition_val:
       do some thing

while active_condition_val: 
  do some thing
  if conditional_val: 
      break

while active_condion_val:
  if condition_val:
    continue
  do some thing

2. while 例子

输入数字

# -*- coding" utf-8 -*-
message = 'Please enter the numer: '
message += '(Enter \'-1\' when your are finished.)'

while True:
    num = input(message)
    num = int(num)
    if -1 == num:
        break
    print(num)

其代码输出结果如下：

Please enter the numer: (Enter '-1' when your are finished.)1
1
Please enter the numer: (Enter '-1' when your are finished.)2
2
Please enter the numer: (Enter '-1' when your are finished.)3
3
Please enter the numer: (Enter '-1' when your are finished.)4
4
Please enter the numer: (Enter '-1' when your are finished.)5
5
Please enter the numer: (Enter '-1' when your are finished.)-1
------------------
(program exited with code: 0)

打印奇数

  index=0
  while index < 10:
      index = index+1
      if index%2==0:
          continue
      print(index)

其输出结果如下：

1
3
5
7
9


------------------
(program exited with code: 0)

处理列表

stus=['Alice', 'Bob', 'Cedar']
peoples=[]
print(stus)
print(peoples)
while stus:
    stu=stus.pop();
    peoples.append(stu)

print(stus)
print(peoples)

其输出结果如下：

['Alice', 'Bob', 'Cedar']
[]
[]
['Cedar', 'Bob', 'Alice']


------------------
(program exited with code: 0)

删除列表中的元素

stus=['Alice', 'Bob', 'Cedar', 'Bob', 'Joe']

print(stus)
while 'Bob' in stus:
    stus.remove('Bob')

print(stus)

其输出结果如下：

['Alice', 'Bob', 'Cedar', 'Bob', 'Joe']
['Alice', 'Cedar', 'Joe']


------------------
(program exited with code: 0)