Python中for迴圈搭配else的陷阱

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假設有如下代碼：

for i in range(10):    if i == 5:        print ‘found it! i = %s‘ % ielse:    print ‘not found it ...‘

 

你期望的結果是，當找到5時列印出：

found it! i = 5

 

實際上列印出來的結果為：

found it! i = 5not found it ...

 

顯然這不是我們期望的結果。

根據官方文檔說法：

>When the items are exhausted (which is immediately when the sequence is empty), the suite in the else clause, if present, is executed, and the loop terminates.>A break statement executed in the first suite terminates the loop without executing the else clause’s suite. A continue statement executed in the first suite skips the rest of the suite and continues with the next item, or with the else clause if there was no next item.https://docs.python.org/2/reference/compound_stmts.html#the-for-statement

 

大意是說當迭代的對象迭代完並為空白時，位於else的子句將執行，而如果在for迴圈中含有break時則直接終止迴圈，並不會執行else子句。

所以正確的寫法應該為：

for i in range(10):    if i == 5:        print ‘found it! i = %s‘ % i        breakelse:    print ‘not found it ...‘

 

當使用pylint檢測代碼時會提示 

Else clause on loop without a break statement (useless-else-on-loop)

 

所以養成使用pylint檢測代碼的習慣還是很有必要的，像這種邏輯錯誤不注意點還是很難發現的。

唔~

 

轉載自： https://www.cnblogs.com/dspace/p/6622799.html

Python中for迴圈搭配else的陷阱