Question

我刚开始学习python，我想知道出了什么问题这个for循环和/或if语句。

我试图循环查看单词列表，如果我找到的话单词“right”我想用“left”替换它。

def left_join(phrases):                
"""                 
    Join strings and replace "right" to "left"            
"""               

    mlist = list(phrases) 

    for word in mlist:

        if word == "right":
             word = "left"

    output = ','.join(mlist)
    return output    

phrases = ("left", "right", "left", "stop")
left_join(phrases)

我应该得到这个

"left,left,left,stop"

但我得到

"left,right,left,stop"

所以“右”不会被“左”所取代。为什么呢？

Answer 1

引用official documentation on for loop，

为expression_list的结果创建了一个迭代器。然后，对于迭代器提供的每个项，按升序索引的顺序执行一次该套件。

因此re不会更改，此处仅更改>>> import re >>> string = "/foo13546897/bar/Atlantis-GPS-coordinates/bar457822368/foo/" >>> re.search(r'(?<=/bar/)[^/]+(?=/)', string).group() 'Atlantis-GPS-coordinates'

Answer 2

请尝试以下代码：

def left_join(phrases):                
    """                 
         Join strings and replace "right" to "left"            
    """               

    mlist = list(phrases) 

    for i  in range(len(mlist)):

        if mlist[i] == "right":
            mlist[i] = "left"

    output = ','.join(mlist)
    return output    

phrases = ("left", "right", "left", "stop")
output = left_join(phrases)
print(output)

试着学习基本的for循环和/或if语句

2 个答案: