blocks|key|1273652|text|使用pipe()并写入适当的文件描述符。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1273653|https://docs.python.org/library/os.html#file-descriptor-operations|1273654|entityMap|0|LINK|mutability|MUTABLE|url^0|2|6|0|0|1U|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|R|8|@]|D|@$9|S|A|T|1|U]]|E|$]]|$1|H|3|-4|5|6|7|V|8|@]|D|@]|E|$]]]|I|$J|$5|K|L|M|E|$N|G]]]]

Use <code>pipe()</code> and write to the appropriate file descriptor.

<a href="https://docs.python.org/library/os.html#file-descriptor-operations" rel="nofollow noreferrer">https://docs.python.org/library/os.html#file-descriptor-operations</a>

blocks|key|1488335|text|from+cStringIO+import+StringIO+#+Python3+use:+from+io+import+StringIO
import+sys

old_stdout+=+sys.stdout
sys.stdout+=+mystdout+=+StringIO()

#+blah+blah+lots+of+code+...

sys.stdout+=+old_stdout

#+examine+mystdout.getvalue()|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1488336|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>from cStringIO import StringIO # Python3 use: from io import StringIO
import sys

old_stdout = sys.stdout
sys.stdout = mystdout = StringIO()

# blah blah lots of code ...

sys.stdout = old_stdout

# examine mystdout.getvalue()
</code></pre>

blocks|key|1273733|text|从Python2.6开始，您可以使用来自io模块的任何实现TextIOBase+API的东西作为替代。这个解决方案还使您能够使用Python3中的sys.stdout.buffer.write()将(已经)编码的字节字符串写入标准输出(请参阅stdout+in+Python+3)。使用StringIO是行不通的，因为sys.stdout.encoding和sys.stdout.buffer都不可用。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1273734|使用TextIOWrapper的解决方案：|1273735|import+sys
from+io+import+TextIOWrapper,+BytesIO

#+setup+the+environment
old_stdout+=+sys.stdout
sys.stdout+=+TextIOWrapper(BytesIO(),+sys.stdout.encoding)

#+do+something+that+writes+to+stdout+or+stdout.buffer

#+get+output
sys.stdout.seek(0)++++++#+jump+to+the+start
out+=+sys.stdout.read()+#+read+output

#+restore+stdout
sys.stdout.close()
sys.stdout+=+old_stdout|code-block|syntax|javascript|1273736|此解决方案适用于Python2、>=+2.6和Python3。|1273737|请注意，我们的新sys.stdout.write()只接受unicode字符串，而sys.stdout.buffer.write()只接受字节字符串。对于旧代码可能不是这种情况，但对于构建为在Python2和3上运行的代码通常是这种情况，不需要更改，这也经常使用sys.stdout.buffer。|1273738|您可以为write()构建一个接受unicode和字节字符串的微小变体。|1273739|class+StdoutBuffer(TextIOWrapper):
++++def+write(self,+string):
++++++++try:
++++++++++++return+super(StdoutBuffer,+self).write(string)
++++++++except+TypeError:
++++++++++++#+redirect+encoded+byte+strings+directly+to+buffer
++++++++++++return+super(StdoutBuffer,+self).buffer.write(string)|1273740|您不必将缓冲区的编码设置为sys.stdout.encoding，但在使用此方法测试/比较脚本输出时，这会很有帮助。|1273741|entityMap|0|LINK|mutability|MUTABLE|url|http://docs.python.org/2/library/io.html#io.TextIOBase|1|http://docs.python.org/3.0/library/sys.html#sys.stdout^0|T|A|21|P|3Z|8|4F|J|4Z|H|T|E|0|3D|I|1|0|0|0|0|8|I|15|P|3N|H|0|4|7|0|0|0^^$0|@$1|2|3|4|5|6|7|16|8|@$9|17|A|18|B|C]|$9|19|A|1A|B|C]|$9|1B|A|1C|B|C]|$9|1D|A|1E|B|C]|$9|1F|A|1G|B|C]]|D|@$9|1H|A|1I|1|1J]|$9|1K|A|1L|1|1M]]|E|$]]|$1|F|3|G|5|6|7|1N|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|1O|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|1P|8|@]|D|@]|E|$]]|$1|O|3|P|5|6|7|1Q|8|@$9|1R|A|1S|B|C]|$9|1T|A|1U|B|C]|$9|1V|A|1W|B|C]]|D|@]|E|$]]|$1|Q|3|R|5|6|7|1X|8|@$9|1Y|A|1Z|B|C]]|D|@]|E|$]]|$1|S|3|T|5|J|7|20|8|@]|D|@]|E|$K|L]]|$1|U|3|V|5|6|7|21|8|@]|D|@]|E|$]]|$1|W|3|-4|5|6|7|22|8|@]|D|@]|E|$]]]|X|$Y|$5|Z|10|11|E|$12|13]]|14|$5|Z|10|11|E|$12|15]]]]

Starting with Python 2.6 you can use anything implementing the <a href="http://docs.python.org/2/library/io.html#io.TextIOBase" rel="noreferrer"><code>TextIOBase</code> API</a> from the io module as a replacement.
This solution also enables you to use <code>sys.stdout.buffer.write()</code> in Python 3 to write (already) encoded byte strings to stdout (see <a href="http://docs.python.org/3.0/library/sys.html#sys.stdout" rel="noreferrer">stdout in Python 3</a>).
Using <code>StringIO</code> wouldn't work then, because neither <code>sys.stdout.encoding</code> nor <code>sys.stdout.buffer</code> would be available.

A solution using TextIOWrapper:

<pre><code>import sys
from io import TextIOWrapper, BytesIO

# setup the environment
old_stdout = sys.stdout
sys.stdout = TextIOWrapper(BytesIO(), sys.stdout.encoding)

# do something that writes to stdout or stdout.buffer

# get output
sys.stdout.seek(0) # jump to the start
out = sys.stdout.read() # read output

# restore stdout
sys.stdout.close()
sys.stdout = old_stdout
</code></pre>

This solution works for Python 2 >= 2.6 and Python 3.

Please note that our new <code>sys.stdout.write()</code> only accepts unicode strings and <code>sys.stdout.buffer.write()</code> only accepts byte strings.
This might not be the case for old code, but is often the case for code that is built to run on Python 2 and 3 without changes, which again often makes use of <code>sys.stdout.buffer</code>.

You can build a slight variation that accepts unicode and byte strings for <code>write()</code>:

<pre><code>class StdoutBuffer(TextIOWrapper):
 def write(self, string):
 try:
 return super(StdoutBuffer, self).write(string)
 except TypeError:
 # redirect encoded byte strings directly to buffer
 return super(StdoutBuffer, self).buffer.write(string)
</code></pre>

You don't have to set the encoding of the buffer the sys.stdout.encoding, but this helps when using this method for testing/comparing script output.

blocks|key|1488422|text|Python+3.4%2B中有一个contextlib.redirect_stdout()+function：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1488423|import+io
from+contextlib+import+redirect_stdout

with+io.StringIO()+as+buf,+redirect_stdout(buf):
++++print('redirected')
++++output+=+buf.getvalue()|code-block|syntax|javascript|1488424|这是一个code+example+that+shows+how+to+implement+it+on+older+Python+versions。|1488425|entityMap|0|LINK|mutability|MUTABLE|url|http://docs.python.org/3/library/contextlib.html#contextlib.redirect_stdout|1|https://stackoverflow.com/a/22434262^0|F|S|F|11|0|0|0|4|1W|1|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]]|D|@$9|Z|A|10|1|11]]|E|$]]|$1|F|3|G|5|H|7|12|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|13|8|@]|D|@$9|14|A|15|1|16]]|E|$]]|$1|M|3|-4|5|6|7|17|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]|U|$5|P|Q|R|E|$S|V]]]]

There is a <a href="http://docs.python.org/3/library/contextlib.html#contextlib.redirect_stdout" rel="noreferrer"><code>contextlib.redirect_stdout()</code> function</a> in Python 3.4+:
<pre><code>import io
from contextlib import redirect_stdout

with io.StringIO() as buf, redirect_stdout(buf):
 print('redirected')
 output = buf.getvalue()
</code></pre>
Here's a <a href="https://stackoverflow.com/a/22434262">code example that shows how to implement it on older Python versions</a>.

blocks|key|1273796|text|在Python3.6中，StringIO和cStringIO模块消失了，你应该使用io.StringIO+instead.So你应该像第一个答案那样做：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1273797|import+sys
from+io+import+StringIO

old_stdout+=+sys.stdout
old_stderr+=+sys.stderr
my_stdout+=+sys.stdout+=+StringIO()
my_stderr+=+sys.stderr+=+StringIO()

#+blah+blah+lots+of+code+...

sys.stdout+=+self.old_stdout
sys.stderr+=+self.old_stderr

//+if+you+want+to+see+the+value+of+redirect+output,+be+sure+the+std+output+is+turn+back
print(my_stdout.getvalue())
print(my_stderr.getvalue())

my_stdout.close()
my_stderr.close()|code-block|syntax|javascript|1273798|entityMap^0|C|8|L|9|15|B|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|T|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|U|8|@]|D|@]|E|$]]]|L|$]]

In Python3.6, the <code>StringIO</code> and <code>cStringIO</code> modules are gone, you should use <code>io.StringIO</code> instead.So you should do this like the first answer:

<pre><code>import sys
from io import StringIO

old_stdout = sys.stdout
old_stderr = sys.stderr
my_stdout = sys.stdout = StringIO()
my_stderr = sys.stderr = StringIO()

# blah blah lots of code ...

sys.stdout = self.old_stdout
sys.stderr = self.old_stderr

// if you want to see the value of redirect output, be sure the std output is turn back
print(my_stdout.getvalue())
print(my_stderr.getvalue())

my_stdout.close()
my_stderr.close()
</code></pre>

blocks|key|1488500|text|Python3的上下文管理器：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1488501|import+sys
from+io+import+StringIO


class+RedirectedStdout:
++++def+__init__(self):
++++++++self._stdout+=+None
++++++++self._string_io+=+None

++++def+__enter__(self):
++++++++self._stdout+=+sys.stdout
++++++++sys.stdout+=+self._string_io+=+StringIO()
++++++++return+self

++++def+__exit__(self,+type,+value,+traceback):
++++++++sys.stdout+=+self._stdout

++++def+__str__(self):
++++++++return+self._string_io.getvalue()|code-block|syntax|javascript|1488502|像这样使用：|1488503|>>>+with+RedirectedStdout()+as+out:
>>>+++++print('asdf')
>>>+++++s+=+str(out)
>>>+++++print('bsdf')
>>>+print(s,+out)
'asdf\n'+'asdf\nbsdf\n'|1488504|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

A context manager for python3:

<pre><code>import sys
from io import StringIO


class RedirectedStdout:
 def __init__(self):
 self._stdout = None
 self._string_io = None

 def __enter__(self):
 self._stdout = sys.stdout
 sys.stdout = self._string_io = StringIO()
 return self

 def __exit__(self, type, value, traceback):
 sys.stdout = self._stdout

 def __str__(self):
 return self._string_io.getvalue()
</code></pre>

use like this:

<pre><code>&gt;&gt;&gt; with RedirectedStdout() as out:
&gt;&gt;&gt; print('asdf')
&gt;&gt;&gt; s = str(out)
&gt;&gt;&gt; print('bsdf')
&gt;&gt;&gt; print(s, out)
'asdf\n' 'asdf\nbsdf\n'
</code></pre>

blocks|key|1488569|text|这是关于这个的另一个观点。使用io.StringIO()作为documented的contextlib.redirect_stdout很棒，但对于日常使用来说，它仍然有点冗长。下面是如何通过将contextlib.redirect_stdout子类化来使其成为一行程序|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1488570|import+sys
import+io
from+contextlib+import+redirect_stdout

class+capture(redirect_stdout):

++++def+__init__(self):
++++++++self.f+=+io.StringIO()
++++++++self._new_target+=+self.f
++++++++self._old_targets+=+[]++#+verbatim+from+parent+class

++++def+__enter__(self):
++++++++self._old_targets.append(getattr(sys,+self._stream))++#+verbatim+from+parent+class
++++++++setattr(sys,+self._stream,+self._new_target)++#+verbatim+from+parent+class
++++++++return+self++#+instead+of+self._new_target+in+the+parent+class

++++def+__repr__(self):
++++++++return+self.f.getvalue()++|code-block|syntax|javascript|1488571|由于__enter__返回self，因此在with块退出后，您可以使用上下文管理器对象。此外，由于使用了__repr__方法，上下文管理器对象的字符串表示实际上是标准输出。所以现在你有了，|1488572|with+capture()+as+message:
++++print('Hello+World!')
print(str(message)=='Hello+World!\n')++#+returns+True|1488573|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.python.org/3/library/contextlib.html#contextlib.redirect_stdout^0|F|D|15|Q|2O|Q|U|A|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]|$9|Z|A|10|B|C]|$9|11|A|12|B|C]]|D|@$9|13|A|14|1|15]]|E|$]]|$1|F|3|G|5|H|7|16|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|17|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|18|8|@]|D|@]|E|$I|J]]|$1|O|3|-4|5|6|7|19|8|@]|D|@]|E|$]]]|P|$Q|$5|R|S|T|E|$U|V]]]]

Here's another take on this. <code>contextlib.redirect_stdout</code> with <code>io.StringIO()</code> as <a href="https://docs.python.org/3/library/contextlib.html#contextlib.redirect_stdout" rel="nofollow noreferrer">documented</a> is great, but it's still a bit verbose for every day use. Here's how to make it a one-liner by subclassing <code>contextlib.redirect_stdout</code>:

<pre class="lang-py prettyprint-override"><code>import sys
import io
from contextlib import redirect_stdout

class capture(redirect_stdout):

 def __init__(self):
 self.f = io.StringIO()
 self._new_target = self.f
 self._old_targets = [] # verbatim from parent class

 def __enter__(self):
 self._old_targets.append(getattr(sys, self._stream)) # verbatim from parent class
 setattr(sys, self._stream, self._new_target) # verbatim from parent class
 return self # instead of self._new_target in the parent class

 def __repr__(self):
 return self.f.getvalue() 
</code></pre>

Since __enter__ returns self, you have the context manager object available after the with block exits. Moreover, thanks to the __repr__ method, the string representation of the context manager object is, in fact, stdout. So now you have,

<pre class="lang-py prettyprint-override"><code>with capture() as message:
 print('Hello World!')
print(str(message)=='Hello World!\n') # returns True
</code></pre>

I'm using python's <code>ftplib</code> to write a small FTP client, but some of the functions in the package don't return string output, but print to <code>stdout</code>. I want to redirect <code>stdout</code> to an object which I'll be able to read the output from.

I know <code>stdout</code> can be redirected into any regular file with:

<pre><code>stdout = open("file", "a")
</code></pre>

But I prefer a method that doesn't uses the local drive.

I'm looking for something like the <code>BufferedReader</code> in Java that can be used to wrap a buffer into a stream.

Can I redirect the stdout into some sort of string buffer?

Python

Java

我正在使用python的ftplib编写一个小的FTP客户端，但是包中的一些函数并不返回字符串输出，而是打印到stdout。我想将stdout重定向到一个我可以从中读取输出的对象。我知道可以使用以下命令将stdout重定向到任何常规文件：stdout = open("file", "a")但我更喜欢不使用本地驱动器的方...

问我可以将stdout重定向到某种字符串缓冲区吗？
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问我可以将stdout重定向到某种字符串缓冲区吗？
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