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#yyds干货盘点#python循环中的 break、continue 语句及 else 子句

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

循环语句支持 else 子句;for 循环中,可迭代对象中的元素全部循环完毕,或 while 循环的条件为假时,执行该子句;break 语句终止循环时,不执行该子句。 请看下面这个查找素数的循环示例:

>>> 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

(没错,这段代码就是这么写。仔细看:else 子句属于 for 循环,不属于 if 语句。)

与 if 语句相比,循环的 else 子句更像 try 的 else 子句: try 的 else 子句在未触发异常时执行,循环的 else 子句则在未运行 break 时执行。try 语句和异常详见 异常的处理。

continue 语句也借鉴自 C 语言,表示继续执行循环的下一次迭代:

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

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