python之while循环、无限循环用法及说明

while 判断条件：
    语句

a = 100
sum = 0
counter = 1
while counter <= a:
    sum = sum + counter
    counter += 1
print("1到%d之和为: %d"%(a,sum))

var = 1
while var == 1:   #表达式永远为True
    num = int(input("输入一个数字："))
    print("你输入的数字是: ", num)
print("Good Bye!!!")

count = 0
while count < 5:
   print (count, " 小于 5")
   count = count + 1
else:
   print (count, " 大于或等于 5")

flag = 1
while (flag): print ('九尾免费小说欢迎你')
print ("Good bye!")

sites = ["Baidu", "Google","Runoob","Taobao"]
for site in sites:
    if site == "Runoob":
        print("九尾!")
        break
    print("循环数据 " + site)
else:
    print("没有循环数据!")
print("完成循环!")

>>>for i in range(5):
...     print(i)
...
0
1
2
3
4

>>>for i in range(5,9) :
    print(i)
5
6
7
8
>>>

>>>for i in range(0, 10, 3) :
    print(i)
0
3
6
9
>>>

>>>for i in range(-10, -100, -30) :
    print(i)
-10
-40
-70
>>>

>>>a = ['Google', 'Baidu', 'Runoob', 'Taobao', 'QQ']
>>> for i in range(len(a)):
...     print(i, a[i])
... 
0 Google
1 Baidu
2 Runoob
3 Taobao
4 QQ
>>>

>>>list(range(5))
[0, 1, 2, 3, 4]
>>>

for letter in 'Runoob':     # 第一个实例
   if letter == 'b':
      break
   print ('当前字母为 :', letter)
var = 10                    # 第二个实例
while var > 0:              
   print ('当期变量值为 :', var)
   var = var -1
   if var == 5:
      break
print ("Good bye!")

for letter in 'Runoob':     # 第一个实例
   if letter == 'o':        # 字母为 o 时跳过输出
      continue
   print ('当前字母 :', letter)
var = 10                    # 第二个实例
while var > 0:              
   var = var -1
   if var == 5:             # 变量为 5 时跳过输出
      continue
   print ('当前变量值 :', var)
print ("Good bye!")

for n in range(2, 10):
    for x in range(2, n):
        if n % x == 0:
            print(n, '等于', x, '*', n//x)
            break
    else:
        # 循环中没有找到元素
        print(n, ' 是质数')

>>>while True:
...     pass  # 等待键盘中断 (Ctrl+C)

>>>class MyEmptyClass:
...     pass

for letter in 'Runoob': 
   if letter == 'o':
      pass
      print ('执行 pass 块')
   print ('当前字母 :', letter)
print ("Good bye!")