python 循环语句的else语句用法，当循环条件变为假，切不是通过breakbreak终止的时候，就会执行这个else语句。

下面循环搜索质数的代码例示了这一点：

>>>

>>> for n in range(2, 10):
...     for x in range(2, n):
...         if n % x == 0:
...             print n, 'equals', x, '*', n/x
...             break
...     else:
...         # loop fell through without finding a factor
...         print n, 'is a prime number'
...
2 is a prime number
3 is a prime number
4 equals 2 * 2
5 is a prime number
6 equals 2 * 3
7 is a prime number
8 equals 2 * 4
9 equals 3 * 3

if语句。)