break 和 continue 语句, 以及循环中的 else 子句

灰太狼 2021-12-21 10:57 291阅读 0赞

转自： [https://blog.csdn.net/weixin\_34409357/article/details/93881089][https_blog.csdn.net_weixin_34409357_article_details_93881089]

## [来源：http://www.pythondoc.com/pythontutorial3/controlflow.html\#break-continue-else][http_www.pythondoc.com_pythontutorial3_controlflow.html_break-continue-else] ##

## 4.4. [break][] 和 [continue][] 语句, 以及循环中的 [else][] 子句 ##

[break][] 语句和 C 中的类似，用于跳出最近的一级 [for][] 或 [while][] 循环。

循环可以有一个 `else` 子句；它在循环迭代完整个列表（对于 [for][] ）或执行条件为 false （对于 [while][]）时执行，但循环被 [break][] 中止的情况下不会执行。以下搜索素数的示例程序演示了这个子句:

>>> 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

(Yes, 这是正确的代码。看仔细：`else` 语句是属于 [for][] 循环之中， **不是** [if][] 语句。)

与循环一起使用时，`else` 子句与 [try][] 语句的 `else` 子句比与 [if][] 语句的具有更多的共同点：[try][] 语句的`else` 子句在未出现异常时运行，循环的 `else` 子句在未出现 `break` 时运行。更多关于 [try][] 语句和异常的内容，请参见 [异常处理][Link 1]。

[continue][] 语句是从 C 中借鉴来的，它表示循环继续执行下一次迭代:

>>> for num in range(2, 10):
    ...     if num % 2 == 0:
    ...         print("Found an even number", num)
    ...         continue
    ...     print("Found a number", num)
    Found an even number 2
    Found a number 3
    Found an even number 4
    Found a number 5
    Found an even number 6
    Found a number 7
    Found an even number 8
    Found a number 9

转载于:https://www.cnblogs.com/stevenzeng/p/5249554.html

[https_blog.csdn.net_weixin_34409357_article_details_93881089]: https://blog.csdn.net/weixin_34409357/article/details/93881089
[http_www.pythondoc.com_pythontutorial3_controlflow.html_break-continue-else]: http://www.pythondoc.com/pythontutorial3/controlflow.html#break-continue-else
[break]: https://docs.python.org/3/reference/simple_stmts.html#break
[continue]: https://docs.python.org/3/reference/simple_stmts.html#continue
[else]: https://docs.python.org/3/reference/compound_stmts.html#else
[for]: https://docs.python.org/3/reference/compound_stmts.html#for
[while]: https://docs.python.org/3/reference/compound_stmts.html#while
[if]: https://docs.python.org/3/reference/compound_stmts.html#if
[try]: https://docs.python.org/3/reference/compound_stmts.html#try
[Link 1]: http://www.pythondoc.com/pythontutorial3/errors.html#tut-handling