blocks|key|793667|text|您可以使用itertools.tee()|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|793668|walk,+walk2+=+itertools.tee(walk)|code-block|syntax|javascript|793669|请注意，正如文档指出的那样，这可能“需要大量的额外存储”。|793670|entityMap|0|LINK|mutability|MUTABLE|url|http://docs.python.org/library/itertools.html#itertools.tee^0|5|F|5|F|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@$9|X|A|Y|1|Z]]|E|$]]|$1|F|3|G|5|H|7|10|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|11|8|@]|D|@]|E|$]]|$1|M|3|-4|5|6|7|12|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]]]

You can use <a href="http://docs.python.org/library/itertools.html#itertools.tee"><code>itertools.tee()</code></a>:

<pre><code>walk, walk2 = itertools.tee(walk)
</code></pre>

Note that this might "need significant extra storage", as the documentation points out.

blocks|key|793706|text|定义函数|type|unstyled|depth|inlineStyleRanges|entityRanges|data|793707|+def+walk_home():
+++++for+r+in+os.walk('/home'):
+++++++++yield+r|code-block|syntax|javascript|793708|或者甚至是这个|793709|def+walk_home():
++++return+os.walk('/home')|793710|两者的用法都是这样的：|793711|for+root,+dirs,+files+in+walk_home():
++++for+pathname+in+dirs%2Bfiles:
++++++++print+os.path.join(root,+pathname)|793712|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|U|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

Define a function

<pre><code> def walk_home():
 for r in os.walk('/home'):
 yield r
</code></pre>

Or even this

<pre><code>def walk_home():
 return os.walk('/home')
</code></pre>

Both are used like this:

<pre><code>for root, dirs, files in walk_home():
 for pathname in dirs+files:
 print os.path.join(root, pathname)
</code></pre>

blocks|key|1008019|text|如果您知道每次使用都要遍历整个生成器，那么通过将生成器展开为一个列表并多次使用该列表，您可能会获得最佳性能。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1008020|walk+=+list(os.walk('/home'))|offset|length|style|CODE|1008021|entityMap^0|0|0|T|0^^$0|@$1|2|3|4|5|6|7|J|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|K|8|@$D|L|E|M|F|G]]|9|@]|A|$]]|$1|H|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|I|$]]

If you know you are going to iterate through the whole generator for every usage, you will probably get the best performance by unrolling the generator to a list and using the list multiple times.

<code>walk = list(os.walk('/home'))</code>

blocks|key|1008159|text|这段"Python+generator+Listeners“代码允许您在一个生成器上拥有多个侦听器，比如os.walk，甚至可以让某个人稍后”插话“。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1008160|def+walkme()：os.walk('/home')|1008161|m1+=多路复用器(对讲机)+m2+=多路复用器(对讲机)|1008162|然后，m1和m2甚至可以在线程中运行，并在空闲时进行处理。|1008163|请参阅：https://gist.github.com/earonesty/cafa4626a2def6766acf5098331157b3|1008164|import+queue
from+threading+import+Lock
from+collections+import+namedtuple

class+Muxer():
++++Entry+=+namedtuple('Entry',+'genref+listeners,+lock')

++++already+=+{}
++++top_lock+=+Lock()

++++def+__init__(self,+func,+restart=False):
++++++++self.restart+=+restart
++++++++self.func+=+func
++++++++self.queue+=+queue.Queue()

++++++++with+self.top_lock:
++++++++++++if+func+not+in+self.already:
++++++++++++++++self.already[func]+=+self.Entry([func()],+[],+Lock())
++++++++++++ent+=+self.already[func]

++++++++self.genref+=+ent.genref
++++++++self.lock+=+ent.lock
++++++++self.listeners+=+ent.listeners

++++++++self.listeners.append(self)

++++def+__iter__(self):
++++++++return+self

++++def+__next__(self):
++++++++try:
++++++++++++e+=+self.queue.get_nowait()
++++++++except+queue.Empty:
++++++++++++with+self.lock:
++++++++++++++++try:
++++++++++++++++++++e+=+self.queue.get_nowait()
++++++++++++++++except+queue.Empty:
++++++++++++++++++++try:
++++++++++++++++++++++++e+=+next(self.genref[0])
++++++++++++++++++++++++for+other+in+self.listeners:
++++++++++++++++++++++++++++if+not+other+is+self:
++++++++++++++++++++++++++++++++other.queue.put(e)
++++++++++++++++++++except+StopIteration:
++++++++++++++++++++++++if+self.restart:
++++++++++++++++++++++++++++self.genref[0]+=+self.func()
++++++++++++++++++++++++raise
++++++++return+e

++++def+__del__(self):
++++++++with+self.top_lock:
++++++++++++try:
++++++++++++++++self.listeners.remove(self)
++++++++++++except+ValueError:
++++++++++++++++pass
++++++++++++if+not+self.listeners+and+self.func+in+self.already:
++++++++++++++++del+self.already[self.func]|code-block|syntax|javascript|1008165|entityMap|0|LINK|mutability|MUTABLE|url|https://gist.github.com/earonesty/cafa4626a2def6766acf5098331157b3^0|1G|7|0|0|0|0|4|1U|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@$9|11|A|12|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|13|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|14|8|@]|D|@]|E|$]]|$1|J|3|K|5|6|7|15|8|@]|D|@]|E|$]]|$1|L|3|M|5|6|7|16|8|@]|D|@$9|17|A|18|1|19]]|E|$]]|$1|N|3|O|5|P|7|1A|8|@]|D|@]|E|$Q|R]]|$1|S|3|-4|5|6|7|1B|8|@]|D|@]|E|$]]]|T|$U|$5|V|W|X|E|$Y|Z]]]]

This "Python Generator Listeners" code allows you to have many listeners on a single generator, like <code>os.walk</code>, and even have someone "chime in" later.

def walkme():
 os.walk('/home')

m1 = Muxer(walkme)
m2 = Muxer(walkme)

then m1 and m2 can run in threads even and process at their leisure.

See: <a href="https://gist.github.com/earonesty/cafa4626a2def6766acf5098331157b3" rel="nofollow noreferrer">https://gist.github.com/earonesty/cafa4626a2def6766acf5098331157b3</a>

<pre><code>import queue
from threading import Lock
from collections import namedtuple

class Muxer():
 Entry = namedtuple('Entry', 'genref listeners, lock')

 already = {}
 top_lock = Lock()

 def __init__(self, func, restart=False):
 self.restart = restart
 self.func = func
 self.queue = queue.Queue()

 with self.top_lock:
 if func not in self.already:
 self.already[func] = self.Entry([func()], [], Lock())
 ent = self.already[func]

 self.genref = ent.genref
 self.lock = ent.lock
 self.listeners = ent.listeners

 self.listeners.append(self)

 def __iter__(self):
 return self

 def __next__(self):
 try:
 e = self.queue.get_nowait()
 except queue.Empty:
 with self.lock:
 try:
 e = self.queue.get_nowait()
 except queue.Empty:
 try:
 e = next(self.genref[0])
 for other in self.listeners:
 if not other is self:
 other.queue.put(e)
 except StopIteration:
 if self.restart:
 self.genref[0] = self.func()
 raise
 return e

 def __del__(self):
 with self.top_lock:
 try:
 self.listeners.remove(self)
 except ValueError:
 pass
 if not self.listeners and self.func in self.already:
 del self.already[self.func]
</code></pre>

Consider this scenario:
<pre class="lang-py prettyprint-override"><code>#!/usr/bin/env python
# -*- coding: utf-8 -*-
import os

walk = os.walk('/home')

for root, dirs, files in walk:
 for pathname in dirs+files:
 print os.path.join(root, pathname)

for root, dirs, files in walk:
 for pathname in dirs+files:
 print os.path.join(root, pathname)
</code></pre>
I know that this example is kinda redundant, but you should consider that we need to use the same <code>walk</code> data more than once. I've a benchmark scenario and the use of same <code>walk</code> data is mandatory to get helpful results.
I've tried <code>walk2 = walk</code> to clone and use in the second iteration, but it didn't work. The question is... How can I copy it? Is it ever possible?
Thank you in advance.

How to clone a Python generator object?

Python

考虑以下场景：#!/usr/bin/env python# -*- coding: utf-8 -*-import oswalk = os.walk('/home')for root, dirs, files in walk:    for pathname in dirs+files:        print os...

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