python3默认编码标准是,默认编码的Python标准错误？

I've got a noisy python script that I want to silence by directing its stderr output to /dev/null (using bash BTW).

Like so:

python -u parse.py 1> /tmp/output3.txt 2> /dev/null

but it quickly exits prematurely. Hmm. I can't see the traceback because of course that goes out with stderr. It runs noisily and normally if I don't direct stderr somewhere.

So let's try redirecting it to a file somewhere rather than /dev/null, and take a look at what it's outputting:

python -u parse.py 1> /tmp/output3.txt 2> /tmp/foo || tail /tmp/foo

Traceback (most recent call last):

File "parse.py", line 79, in

parseit('pages-articles.xml')

File "parse.py", line 33, in parseit

print >>sys.stderr, "bad page title", page_title

UnicodeEncodeError: 'ascii' codec can't encode characters in position 0-1: ordinal not in range(128)

So, the stderr that's being generated contains utf8, and for some reason python refuses to print non-ascii when it's being redirected, even though it's being directed to /dev/null (though of course python doesn't know that).

How can I silence the stderr of a python script even though it contains utf8? Is there any way to do it without re-writing every print to stderr in this script?

解决方案

You can silence stderr by binding it to a custom writer:

#!/usr/bin/env python

import codecs, sys

class NullWriter:

def write(self, *args, **kwargs):

pass

if len(sys.argv) == 2:

if sys.argv[1] == '1':

sys.stderr = NullWriter()

elif sys.argv[1] == '2':

#NOTE: sys.stderr.encoding is *read-only*

# therefore the whole stderr should be replaced

# encode all output using 'utf8'

sys.stderr = codecs.getwriter('utf8')(sys.stderr)

print >>sys.stderr, u"\u20AC" # euro sign

print "ok"

Example:

$ python silence_stderr.py

Traceback (most recent call last):

File "silence_stderr.py", line 11, in

print >>sys.stderr, u"\u20AC"

UnicodeEncodeError: 'ascii' codec can't encode character u'\u20ac' in position 0: ordinal not in range(128)

Silenced stderr:

$ python silence_stderr.py 1

ok

Encoded stderr:

$ python silence_stderr.py 2

€

ok

NOTE: I've got the above outputs inside emacs therefore to emulate it in a terminal you could do:

$ python ... 2>out.txt

$ cat out.txt

NOTE: Inside Windows console (after chcp 65001 that switch to 'utf-8' and with truetype font (Lucida Console)) I've got strange results:

C:\> python silence_stderr.py 2

Traceback (most recent call last):

File "silence_stderr.py", line 14, in

print >>sys.stderr, u"\u20AC" # euro sign

File "C:\pythonxy\python\lib\codecs.py", line 304, in write

self.stream.write(data)

IOError: [Errno 13] Permission denied

If the font is not truetype then the exception doesn't raise but the output is wrong.

Perl works for the truetype font:

C:\> perl -E"say qq(\x{20ac})"

Wide character in print at -e line 1.

€

Redirection works though:

C:\>python silence_stderr.py 2 2>tmp.log

ok

C:\>cat tmp.log

€

cat: write error: Permission denied

re comment

From codecs.getwriter documentation:

Look up the codec for the given

encoding and return its StreamWriter

class or factory function. Raises a

LookupError in case the encoding

cannot be found.

An oversimplified view:

class UTF8StreamWriter:

def __init__(self, writer):

self.writer = writer

def write(self, s):

self.writer.write(s.encode('utf-8'))

sys.stderr = UTF8StreamWriter(sys.stderr)