blocks|key|618468|text|使用os.walk而不是重复发明轮子。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|618469|特别是，按照库文档中的示例，这里是一次未经测试的尝试：|618470|import+os
from+os.path+import+join

def+hellothere(somepath):
++++for+root,+dirs,+files+in+os.walk(somepath):
++++++++for+curfile+in+files:
++++++++++++yield+join(root,+curfile)


#+call+and+get+full+list+of+results:
allfiles+=+[+x+for+x+in+hellothere("...")+]

#+iterate+over+results+lazily:
for+x+in+hellothere("..."):
++++print+x|code-block|syntax|javascript|618471|entityMap|0|LINK|mutability|MUTABLE|url|http://docs.python.org/library/os.html#os.walk^0|2|7|2|7|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@$9|X|A|Y|1|Z]]|E|$]]|$1|F|3|G|5|6|7|10|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|11|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|12|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]]]

Use <a href="http://docs.python.org/library/os.html#os.walk" rel="noreferrer"><code>os.walk</code></a> instead of reinventing the wheel. 

In particular, following the examples in the library documentation, here is an untested attempt:

<pre><code>import os
from os.path import join

def hellothere(somepath):
 for root, dirs, files in os.walk(somepath):
 for curfile in files:
 yield join(root, curfile)


# call and get full list of results:
allfiles = [ x for x in hellothere("...") ]

# iterate over results lazily:
for x in hellothere("..."):
 print x
</code></pre>

blocks|key|618480|text|试试这个：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|618481|if+stat.S_ISDIR(stat_info.st_mode):
++++for+p+in+explore(path):
++++++++yield+p|code-block|syntax|javascript|618482|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|$]]

Try this:

<pre><code>if stat.S_ISDIR(stat_info.st_mode):
 for p in explore(path):
 yield p
</code></pre>

blocks|key|834142|text|它像调用函数一样调用explore。你应该做的就是像生成器一样迭代它：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|834143|if+stat.S_ISDIR(stat_info.st_mode):
++for+p+in+explore(path):
++++yield+p
else:
++yield+path|code-block|syntax|javascript|834144|编辑:您可以使用os.path.isdir(path)而不是stat模块。|834145|entityMap^0|A|7|0|0|8|J|U|4|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|S|8|@$9|T|A|U|B|C]|$9|V|A|W|B|C]]|D|@]|E|$]]|$1|M|3|-4|5|6|7|X|8|@]|D|@]|E|$]]]|N|$]]

That calls <code>explore</code> like a function. What you should do is iterate it like a generator:

<pre><code>if stat.S_ISDIR(stat_info.st_mode):
 for p in explore(path):
 yield p
else:
 yield path
</code></pre>

EDIT: Instead of the <code>stat</code> module, you could use <code>os.path.isdir(path)</code>.

blocks|key|834234|text|迭代器不会像那样递归工作。您必须重新生成每个结果，方法是替换|type|unstyled|depth|inlineStyleRanges|entityRanges|data|834235|explore(path)|code-block|syntax|javascript|834236|使用类似于|834237|for+value+in+explore(path):
++++yield+value|834238|Python+3.3根据PEP+380中的建议添加了语法yield+from+X来实现此目的。使用它，您可以执行以下操作：|offset|length|style|CODE|834239|yield+from+explore(path)|834240|如果您正在使用generators+as+coroutines，则此语法还支持使用generator.send()将值传回递归调用的生成器。上面的简单for循环不会。|834241|entityMap|0|LINK|mutability|MUTABLE|url|http://python.org/download/releases/3.3.0/|1|http://www.python.org/dev/peps/pep-0380/|2|http://www.python.org/dev/peps/pep-0342/|3|http://docs.python.org/2/reference/expressions.html#generator.send^0|0|0|0|0|S|C|0|A|0|C|7|1|0|0|15|G|23|3|7|O|2|15|G|3|0^^$0|@$1|2|3|4|5|6|7|18|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|19|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|1A|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|1B|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|1C|8|@$M|1D|N|1E|O|P]]|9|@$M|1F|N|1G|1|1H]|$M|1I|N|1J|1|1K]]|A|$]]|$1|Q|3|R|5|D|7|1L|8|@]|9|@]|A|$E|F]]|$1|S|3|T|5|6|7|1M|8|@$M|1N|N|1O|O|P]|$M|1P|N|1Q|O|P]]|9|@$M|1R|N|1S|1|1T]|$M|1U|N|1V|1|1W]]|A|$]]|$1|U|3|-4|5|6|7|1X|8|@]|9|@]|A|$]]]|V|$W|$5|X|Y|Z|A|$10|11]]|12|$5|X|Y|Z|A|$10|13]]|14|$5|X|Y|Z|A|$10|15]]|16|$5|X|Y|Z|A|$10|17]]]]

Iterators do not work recursively like that. You have to re-yield each result, by replacing



<pre class="lang-python prettyprint-override"><code>explore(path)
</code></pre>

with something like

<pre class="lang-python prettyprint-override"><code>for value in explore(path):
 yield value
</code></pre>

<a href="http://python.org/download/releases/3.3.0/">Python 3.3</a> added the syntax <code>yield from X</code>, as proposed in <a href="http://www.python.org/dev/peps/pep-0380/">PEP 380</a>, to serve this purpose. With it you can do this instead:

<pre class="lang-python prettyprint-override"><code>yield from explore(path)
</code></pre>

If you're using <a href="http://www.python.org/dev/peps/pep-0342/">generators as coroutines</a>, this syntax also supports the use of <a href="http://docs.python.org/2/reference/expressions.html#generator.send"><code>generator.send()</code></a> to pass values back into the recursively-invoked generators. The simple <code>for</code> loop above would not.

blocks|key|618705|text|更改此设置：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|618706|explore(path)|code-block|syntax|javascript|618707|要这样做：|618708|for+subpath+in+explore(path):
++++yield+subpath|618709|或者按照phooji的建议使用os.walk+(这是更好的选择)。|offset|length|style|CODE|618710|entityMap^0|0|0|0|0|F|7|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|W|8|@$M|X|N|Y|O|P]]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

Change this:

<pre><code>explore(path)
</code></pre>

To this:

<pre><code>for subpath in explore(path):
 yield subpath
</code></pre>

Or use <code>os.walk</code>, as phooji suggested (which is the better option).

blocks|key|618753|text|如果你需要遍历所有的文件夹和子文件夹，os.walk是很棒的。如果你不需要它，那就像用象枪杀死一只苍蝇。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|618754|然而，对于这种特定的情况，os.walk可能是一种更好的方法。|618755|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

os.walk is great if you need to traverse all the folders and subfolders. If you don't need that, it's like using an elephant gun to kill a fly.

However, for this specific case, os.walk could be a better approach.

blocks|key|618810|text|您还可以使用堆栈实现递归。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|618811|不过，这样做并没有什么好处，除了它是可能的。如果您一开始就在使用python，那么性能上的提升可能不值得。|618812|import+os
import+stat

def+explore(p):
++++'''
++++perform+a+depth+first+search+and+yield+the+path+elements+in+dfs+order
++++++++-implement+the+recursion+using+a+stack+because+a+python+can't+yield+within+a+nested+function+call
++++'''
++++list_t=type(list())
++++st=[[p,0]]
++++while+len(st)>0:
++++++++x=st[-1][0]
++++++++print+x
++++++++i=st[-1][1]

++++++++if+type(x)==list_t:
++++++++++++if+i>=len(x):
++++++++++++++++st.pop(-1)
++++++++++++else:
++++++++++++++++st[-1][1]%2B=1
++++++++++++++++st.append([x[i],0])
++++++++else:
++++++++++++st.pop(-1)
++++++++++++stat_info+=+os.lstat(x)
++++++++++++if+stat.S_ISDIR(stat_info.st_mode):
++++++++++++++++st.append([['%25s/%25s'%25(x,a)+for+a+in+os.listdir(x)],0])
++++++++++++else:
++++++++++++++++yield+x

print+list(explore('.'))|code-block|syntax|javascript|618813|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|$]]

You can also implement the recursion using a stack.

There is not really any advantage in doing this though, other than the fact that it is possible. If you are using python in the first place, the performance gains are probably not worthwhile.

<pre><code>import os
import stat

def explore(p):
 '''
 perform a depth first search and yield the path elements in dfs order
 -implement the recursion using a stack because a python can't yield within a nested function call
 '''
 list_t=type(list())
 st=[[p,0]]
 while len(st)&gt;0:
 x=st[-1][0]
 print x
 i=st[-1][1]

 if type(x)==list_t:
 if i&gt;=len(x):
 st.pop(-1)
 else:
 st[-1][1]+=1
 st.append([x[i],0])
 else:
 st.pop(-1)
 stat_info = os.lstat(x)
 if stat.S_ISDIR(stat_info.st_mode):
 st.append([['%s/%s'%(x,a) for a in os.listdir(x)],0])
 else:
 yield x

print list(explore('.'))
</code></pre>

blocks|key|834433|text|要回答最初提出的问题，关键是需要将yield语句传播到递归之外(就像return一样)。下面是os.walk()的重新实现。我在一个伪VFS实现中使用了它，在这个实现中我还替换了os.listdir()和类似的调用。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|834434|import+os,+os.path
def+walk+(top,+topdown=False):
++++items+=+([],+[])
++++for+name+in+os.listdir(top):
++++++++isdir+=+os.path.isdir(os.path.join(top,+name))
++++++++items[isdir].append(name)
++++result+=+(top,+items[True],+items[False])
++++if+topdown:
++++++++yield+result
++++for+folder+in+items[True]:
++++++++for+item+in+walk(os.path.join(top,+folder),+topdown=topdown):
++++++++++++yield+item
++++if+not+topdown:
++++++++yield+result|code-block|syntax|javascript|834435|entityMap^0|H|5|Y|6|1B|9|2H|C|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]|$9|R|A|S|B|C]|$9|T|A|U|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|V|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|W|8|@]|D|@]|E|$]]]|L|$]]

To answer the original question as asked, the key is that the <code>yield</code> statement needs to be propagated back out of the recursion (just like, say, <code>return</code>). Here is a working reimplementation of <code>os.walk()</code>. I'm using this in a pseudo-VFS implementation, where I additionally replace <code>os.listdir()</code> and similar calls.

<pre><code>import os, os.path
def walk (top, topdown=False):
 items = ([], [])
 for name in os.listdir(top):
 isdir = os.path.isdir(os.path.join(top, name))
 items[isdir].append(name)
 result = (top, items[True], items[False])
 if topdown:
 yield result
 for folder in items[True]:
 for item in walk(os.path.join(top, folder), topdown=topdown):
 yield item
 if not topdown:
 yield result
</code></pre>

I am trying to do something to all the files under a given path. I don't want to collect all the file names beforehand then do something with them, so I tried this:

<pre><code>import os
import stat

def explore(p):
 s = ''
 list = os.listdir(p)
 for a in list:
 path = p + '/' + a
 stat_info = os.lstat(path )
 if stat.S_ISDIR(stat_info.st_mode):
 explore(path)
 else:
 yield path

if __name__ == "__main__":
 for x in explore('.'):
 print '--&gt;', x
</code></pre>

But this code skips over directories when it hits them, instead of yielding their contents. What am I doing wrong?

Yield in a recursive function

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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我正在尝试对给定路径下的所有文件执行某些操作。我不想事先收集所有的文件名，然后再对它们做一些事情，所以我尝试这样做：import osimport statdef explore(p):  s = ''  list = os.listdir(p)  for a in list:    path = p + '/' + ...

问递归函数中的Yield
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