blocks|key|2745302|text|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2745303|是循环中的arg吗？|blockquote|2745304|2745305|2745306|是的，它包含一份参考资料的副本。|2745307|当您重新分配arg时，您没有修改原始数组，也没有修改其中的字符串(字符串是不可变的)。只修改局部变量arg指向的内容。|offset|length|style|CODE|2745308|Before+assignment+++++++++After+assignment

args++++++++++arg++++++++++args++++++++++arg
++%7C++++++++++++%7C++++++++++++%7C++++++++++++%7C
++%7C++++++++++++%7C++++++++++++%7C++++++++++++%7C
(array)++++++++/++++++++++(array)+++++++'sdfkj'
++%7C[0]++++++++/+++++++++++++%7C[0]++++++++
+++\+++++++++/++++++++++++++%7C
++++\+++++++/+++++++++++++++%7C
+++++'-sdfkj'++++++++++++'-sdfkj'|code-block|syntax|javascript|2745309|entityMap^0|0|0|0|0|0|6|3|1E|3|0|0^^$0|@$1|2|3|-4|4|5|6|U|7|@]|8|@]|9|$]]|$1|A|3|B|4|C|6|V|7|@]|8|@]|9|$]]|$1|D|3|-4|4|5|6|W|7|@]|8|@]|9|$]]|$1|E|3|-4|4|5|6|X|7|@]|8|@]|9|$]]|$1|F|3|G|4|5|6|Y|7|@]|8|@]|9|$]]|$1|H|3|I|4|5|6|Z|7|@$J|10|K|11|L|M]|$J|12|K|13|L|M]]|8|@]|9|$]]|$1|N|3|O|4|P|6|14|7|@]|8|@]|9|$Q|R]]|$1|S|3|-4|4|5|6|15|7|@]|8|@]|9|$]]]|T|$]]

<blockquote>
 Is arg in the loop a copy?
</blockquote>

Yes, it contains a copy of the reference.

When you reassign <code>arg</code> you aren't modifying the original array, nor the string inside it (strings are immutable). You modify only what the local variable <code>arg</code> points to. 

<pre><code>Before assignment After assignment

args arg args arg
 | | | |
 | | | |
(array) / (array) 'sdfkj'
 |[0] / |[0] 
 \ / |
 \ / |
 '-sdfkj' '-sdfkj'
</code></pre>

blocks|key|1318996|text|既然你在你的问题中提到，你知道可以用列表理解来完成，所以我不打算向你展示这种方式。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1318997|正在发生的情况是，对每个值的引用被复制到变量arg中。最初，它们都引用相同的变量。重新分配arg后，它引用新创建的变量，而列表中的引用保持不变。这与字符串在Python中是不可变的这一事实无关。尝试使用可变类型。|offset|length|style|CODE|1318998|一种非列表理解的方法是修改列表：|1318999|for+i+in+xrange(len(args)):
++++args[i]=args[i].replace('-','')
print+args|code-block|syntax|javascript|1319000|entityMap^0|0|M|3|19|3|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|R|8|@$D|S|E|T|F|G]|$D|U|E|V|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|W|8|@]|9|@]|A|$]]|$1|J|3|K|5|L|7|X|8|@]|9|@]|A|$M|N]]|$1|O|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|P|$]]

Since you mention in your question that you know it can be done using list comprehensions, I'm not going to show you that way.

What is happening there is that the reference to each value is copied into the variable <code>arg</code>. Initially they both refer to the same variable. Once <code>arg</code> is reassigned, it refers to the newly created variable, while the reference in the list remains unchanged. It has nothing to do with the fact that strings are immutable in Python. Try it out using mutable types.

A non-list comprehension way would be to modify the list in place:

<pre><code>for i in xrange(len(args)):
 args[i]=args[i].replace('-','')
print args
</code></pre>

blocks|key|2702389|text|如果要修改实际列表，则必须将更改具体分配给列表'args.‘’。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2702390|即|2702391|for+arg+in+args:
++++if+arg+==+"-":
++++++++args[arg]+=+args[arg].replace("-",+'')|code-block|syntax|javascript|2702392|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|L|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|M|8|@]|9|@]|A|$G|H]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

If you want to modify the actual list you have to specifically assign the changes to the list 'args.'

i.e. 

<pre><code>for arg in args:
 if arg == "-":
 args[arg] = args[arg].replace("-", '')
</code></pre>

blocks|key|2745402|text|想要一份清单，我会尝试：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2745403|args+=+[x.replace("-",+'')+for+x+in+args]|code-block|syntax|javascript|2745404|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

for a list I'd try:

<pre><code>args = [x.replace("-", '') for x in args]
</code></pre>

Consider:

<pre><code>args = ['-sdfkj']
print args
for arg in args:
 print arg.replace("-", '')
 arg = arg.replace("-", '')
print args
</code></pre>

This yields:

<pre><code>['-sdfkj']
sdfkj
['-sdfkj']
</code></pre>

Where I expected it to be <code>['sdfkj']</code>.

Is <code>arg</code> in the loop a copy?

It behaves as if it is a copy (or perhaps an immutable thingie, but then I expect an error would be thrown...)

Note: I can get the right behavior with a list comprehension. I am curious as to the cause of the above behavior.

Semantics of python loops and strings

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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考虑：args = ['-sdfkj']print argsfor arg in args:    print arg.replace("-", '')    arg = arg.replace("-", '')print args这产生了：['-sdfkj']sdfkj['-sdfkj']我以为它是['sdfkj']...

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