stderr的python的默认编码？

Question

我有一个嘈杂的python脚本,我想通过将其stderr输出指向/ dev/null(使用bash BTW)来保持沉默.

像这样:

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

但它很快就会过早退出.嗯.我无法看到追溯因为当然与stderr一起出现了.如果我不指示某个地方的stderr,它会吵闹地运行.

因此,让我们尝试将其重定向到某个地方的文件而不是/ dev/null,并查看它的输出内容:

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 <module>
    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)

因此,正在生成的stderr包含utf8,并且由于某种原因,python在被重定向时拒绝打印非ascii,即使它被定向到/ dev/null(当然python当然不知道).

即使它包含utf8,我如何使python脚本的stderr静音？有没有办法在没有重写这个脚本中的每个打印到stderr？

Answer 1

您可以通过将stderr绑定到自定义编写器来使其静音:

#!/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"

例:

$ python silence_stderr.py
Traceback (most recent call last):
  File "silence_stderr.py", line 11, in <module>
    print >>sys.stderr, u"\u20AC"
UnicodeEncodeError: 'ascii' codec can't encode character u'\u20ac' in position 0: ordinal not in range(128)

沉默的stderr:

$ python silence_stderr.py 1
ok

编码stderr:

$ python silence_stderr.py 2
€
ok

注意:我在emacs中有上面的输出,因此可以在你可以做的终端中模拟它:

$ python ... 2>out.txt
$ cat out.txt

注意:在Windows控制台内部(在chcp 65001切换到'utf-8'并使用truetype font(Lucida Console)之后),我得到了奇怪的结果:

C:\> python silence_stderr.py 2
Traceback (most recent call last):
  File "silence_stderr.py", line 14, in <module>
    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

如果字体不是truetype,则异常不会引发但输出错误.

Perl适用于truetype字体:

C:\> perl  -E"say qq(\x{20ac})"
Wide character in print at -e line 1.
€

重定向虽然有效:

C:\>python silence_stderr.py 2 2>tmp.log
ok
C:\>cat tmp.log
€
cat: write error: Permission denied

评论

来自codecs.getwriter文档:

查找给定编码的编解码器并返回其StreamWriter类或工厂函数.LookupError如果找不到编码,则引发a .

过于简化的观点:

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)