将 python 标准输出重定向到文件失败并出现 UnicodeEncodeError

Question

我有一个 python 脚本，它连接到 Twitter Firehose 并将数据发送到下游进行处理。在它工作正常之前，但现在我试图只获取文本正文。 （这不是关于我应该如何从 Twitter 中提取数据或如何编码/解码 ascii 字符的问题）。所以当我像这样直接启动我的脚本时：

python -u fetch_script.py

它工作得很好，我可以看到屏幕上出现了消息。例如：

root@domU-xx-xx-xx-xx:/usr/local/streaming# python -u fetch_script.py 
Cuz I'm checking you out >on Facebook<
RT @SearchlightNV: #BarryLies???????? has crapped on all honest patriotic hard-working citizens in the USA but his abuse of WWII Vets is sick #2A…
"Why do men chase after women? Because they fear death."~Moonstruck
RT @SearchlightNV: #BarryLies???????? has crapped on all honest patriotic hard-working citizens in the USA but his abuse of WWII Vets is sick #2A…
Never let anyone tell you not to chase your dreams. My sister came home crying today, because someone told her she's not good enough.
"I can't even ask anyone out on a date because if it doesn't end up in a high speed chase, I get bored."
RT @ColIegeStudent: Double-checking the attendance policy while still in bed
Well I just handed my life savings to ya.. #trustingyou #abouttomakebankkkkk
Zillow $Z and Redfin useless to Wells Fargo Home Mortgage, $WFC, and FannieMae $FNM. Sale history LTV now 48%, $360 appraisal fee 4 no PMI.
The latest Dump and Chase Podcast http://somedomain.com/viaRSA9W3i check it out and subscribe on iTunes, or your favorite android app #Isles

但如果我尝试像这样将它们输出到文件中：

python -u fetch_script.py >fetch_output.txt

它立即抛出一个错误：

root@domU-xx-xx-xx-xx:/usr/local/streaming# python -u fetch_script.py >fetch_output.txt
ERROR:tornado.application:Uncaught exception, closing connection.
Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/tornado/iostream.py", line 341, in wrapper
    callback(*args)
  File "/usr/local/lib/python2.7/dist-packages/tornado/stack_context.py", line 331, in wrapped
    raise_exc_info(exc)
  File "/usr/local/lib/python2.7/dist-packages/tornado/stack_context.py", line 302, in wrapped
    ret = fn(*args, **kwargs)
  File "/usr/local/streaming/twitter-stream.py", line 203, in parse_json
    self.parse_response(response)
  File "/usr/local/streaming/twitter-stream.py", line 226, in parse_response
    self._callback(response)
  File "fetch_script.py", line 57, in callback
    print msg['text']
UnicodeEncodeError: 'ascii' codec can't encode character u'\u2026' in position 139: ordinal not in range(128)
ERROR:tornado.application:Exception in callback <functools.partial object at 0x187c2b8>
Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/tornado/ioloop.py", line 458, in _run_callback
    callback()
  File "/usr/local/lib/python2.7/dist-packages/tornado/stack_context.py", line 331, in wrapped
    raise_exc_info(exc)
  File "/usr/local/lib/python2.7/dist-packages/tornado/stack_context.py", line 302, in wrapped
    ret = fn(*args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/tornado/iostream.py", line 341, in wrapper
    callback(*args)
  File "/usr/local/lib/python2.7/dist-packages/tornado/stack_context.py", line 331, in wrapped
    raise_exc_info(exc)
  File "/usr/local/lib/python2.7/dist-packages/tornado/stack_context.py", line 302, in wrapped
    ret = fn(*args, **kwargs)
  File "/usr/local/streaming/twitter-stream.py", line 203, in parse_json
    self.parse_response(response)
  File "/usr/local/streaming/twitter-stream.py", line 226, in parse_response
    self._callback(response)
  File "fetch_script.py", line 57, in callback
    print msg['text']
UnicodeEncodeError: 'ascii' codec can't encode character u'\u2026' in position 139: ordinal not in range(128)

附言

更多上下文：

callback 函数发生错误：

def callback(self, message):
        if message:
            msg = message
            msg_props = pika.BasicProperties()
            msg_props.content_type = 'application/text'
            msg_props.delivery_mode = 2
            #print self.count
            print msg['text']
            #self.count += 1
            ...

但是如果我删除 ['text'] 并且只活在print msg 这两种情况都像一个魅力。

Answer 1

既然还没有人跳进去，那我就开枪了。 Python 在写入控制台时设置标准输出的编码，但在写入文件时不设置。这个脚本重现了这个问题：

import sys

msg = {'text':u'\2026'}
sys.stderr.write('default encoding: %s\n' % sys.stdout.encoding)
print msg['text']

上面运行的时候报错：

$ python bad.py>/tmp/xxx
default encoding: None
Traceback (most recent call last):
  File "fix.py", line 5, in <module>
    print msg['text']
UnicodeEncodeError: 'ascii' codec can't encode character u'\x82' in position 0: ordinal not in range(128)

将编码添加到上述脚本中：

import sys

msg = {'text':u'\2026'}
sys.stderr.write('default encoding: %s\n' % sys.stdout.encoding)
encoding = sys.stdout.encoding or 'utf-8'
print msg['text'].encode(encoding)

问题解决了：

$ python good.py >/tmp/xxx
default encoding: None
$ cat /tmp/xxx
6