Python编程语言允许在一个循环内嵌套另一个循环。下面将介绍几个例子来说明这一概念。

语法

在Python中嵌套循环语句的语法如下：

for iterating_var in sequence:
   for iterating_var in sequence:
      statements(s)
   statements(s)

Python编程语言的一个嵌套while循环语句的语法，如下所示：

while expression:
   while expression:
      statement(s)
   statement(s)

在循环嵌套最后需要说明的是，可以把任何类型的循环的任何其他类型的循环里面。例如，for循环内可以放置while循环，反之亦然。

例子

下面的程序使用一个嵌套的循环，从2到100中找出所有的素数：

#!/usr/bin/python

i = 2
while(i < 100):
   j = 2
   while(j <= (i/j)):
      if not(i%j): break
      j = j + 1
   if (j > i/j) : print i, " is prime"
   i = i + 1

print "Good bye!"

当执行上面的代码，它会产生以下结果：

2 is prime
3 is prime
5 is prime
7 is prime
11 is prime
13 is prime
17 is prime
19 is prime
23 is prime
29 is prime
31 is prime
37 is prime
41 is prime
43 is prime
47 is prime
53 is prime
59 is prime
61 is prime
67 is prime
71 is prime
73 is prime
79 is prime
83 is prime
89 is prime
97 is prime
Good bye!