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发表于： **2016-07-27 19:12**

为何这段Python代码死循环?Python解释器的Bug?
Python版本: 3.4.2

代码：全选

words = ['cat', 'window', 'defenestrate']
for w in words:  # Loop over a slice copy of the entire list.
 if len(w) > 6:
  words.insert(0, w)

If you need to modify the sequence you are iterating over while inside the loop (for example to duplicate selected items), it is recommended that you first make a copy. Iterating over a sequence does not implicitly make a copy. The slice notation makes this especially convenient

https://docs.python.org/3.4/tutorial/co ... statements
我试着把slice去掉了,结果就死循环?

发表于： **2016-07-27 19:46**

我猜是这样的吧：

代码：全选

for w in words:

实际执行的流程大概是这样，先检查 words[0]，words[1]，words[2] ...
上例中如果使用 slice 建了个 copy 的话，检查到 words[3] 发现已经到结尾了就结束了。
但没建 copy 的情况下，在 words[2] 执行的时候 insert 插入了新项到 words 中，
那么原来的 'defenestrate' 从 words[2] 变成了 words[3]，
检查 words[3] 的时候会继续插入把它变成 words[4]，就死循环了。

发表于： **2016-07-27 20:03**

参考
http://stackoverflow.com/questions/1637 ... -iterating
http://effbot.org/zone/python-list.htm#modifying
https://unspecified.wordpress.com/2009/ ... iteration/
https://asmeurersympy.wordpress.com/200 ... in-python/
https://www.smallsurething.com/how-to-m ... in-python/
http://stackoverflow.com/questions/4081 ... g-for-loop

发表于： **2016-07-27 20:19**

弄个调试输出就一目了然了

代码：全选

words = ['cat', 'window', 'defenestrate']
for w in words:  # Loop over a slice copy of the entire list.
    print(len(words))
    print(w)
    if len(w) > 6:
        words.insert(0, w)

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[已解决,非解释器Bug]为何这段Python代码死循环?Python解释器的Bug?

[已解决,非解释器Bug]为何这段Python代码死循环?Python解释器的Bug?

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Re: 为何这段Python代码死循环?Python解释器的Bug?

Re: 为何这段Python代码死循环?Python解释器的Bug?