Google App Engine, Python2.7的UnicodeDecodeError bug

在跟Web Development，要在Google App Engine上写作业，出师不利，遇到以下bug：

2014-05-06 16:14:17 Running command: "['C:\\Python27\\python.exe', 'C:\\Program Files (x86)\\Google\\google_appengine\\dev_appserver.py', '--skip_sdk_update_check=yes', '--port=8080', '--admin_port=8000', 'E:\\GoogleAppEngine\\hello_udacity']"
Traceback (most recent call last):
  File "C:\Program Files (x86)\Google\google_appengine\dev_appserver.py", line 82, in <module>
    _run_file(__file__, globals())
  File "C:\Program Files (x86)\Google\google_appengine\dev_appserver.py", line 78, in _run_file
    execfile(_PATHS.script_file(script_name), globals_)
  File "C:\Program Files (x86)\Google\google_appengine\google\appengine\tools\devappserver2\devappserver2.py", line 33, in <module>
    from google.appengine.tools.devappserver2.admin import admin_server
  File "C:\Program Files (x86)\Google\google_appengine\google\appengine\tools\devappserver2\admin\admin_server.py", line 29, in <module>
    from google.appengine.tools.devappserver2.admin import console
  File "C:\Program Files (x86)\Google\google_appengine\google\appengine\tools\devappserver2\admin\console.py", line 22, in <module>
    from google.appengine.tools.devappserver2 import module
  File "C:\Program Files (x86)\Google\google_appengine\google\appengine\tools\devappserver2\module.py", line 49, in <module>
    from google.appengine.tools.devappserver2 import gcs_server
  File "C:\Program Files (x86)\Google\google_appengine\google\appengine\tools\devappserver2\gcs_server.py", line 29, in <module>
    from google.appengine.tools.devappserver2 import wsgi_server
  File "C:\Program Files (x86)\Google\google_appengine\google\appengine\tools\devappserver2\wsgi_server.py", line 31, in <module>
    from cherrypy import wsgiserver
  File "C:\Program Files (x86)\Google\google_appengine\lib\cherrypy\cherrypy\__init__.py", line 70, in <module>
    from cherrypy import _cptools
  File "C:\Program Files (x86)\Google\google_appengine\lib\cherrypy\cherrypy\_cptools.py", line 245, in <module>
    from cherrypy.lib import cptools, encoding, auth, static, jsontools
  File "C:\Program Files (x86)\Google\google_appengine\lib\cherrypy\cherrypy\lib\static.py", line 7, in <module>
    mimetypes.init()
  File "C:\Python27\lib\mimetypes.py", line 358, in init
    db.read_windows_registry()
  File "C:\Python27\lib\mimetypes.py", line 258, in read_windows_registry
    for subkeyname in enum_types(hkcr):
  File "C:\Python27\lib\mimetypes.py", line 249, in enum_types
    ctype = ctype.encode(default_encoding) # omit in 3.x!
UnicodeDecodeError: 'ascii' codec can't decode byte 0xb0 in position 1: ordinal not in range(128)
2014-05-06 16:14:25 (Process exited with code 1)

经查，此为Python2.7的一个bug。在读取windows注册表中的文件类型列表的时候，Python默认读到的数据为Latin-1编码，因此遇上中文、俄文等等其他类型的编码统统会出错。

闯祸的软件会在注册表里填写恼人的不规范的文件类型。俄文的一个典型是QuickTime，而中文则是阿里旺旺。

On Windows, mimetypes initialization reads the list of MIME types from the Windows registry. It assumes that all characters are Latin-1 encoded, and fails when it's not the case, with the following exception:

Traceback (most recent call last):
  File "mttest.py", line 3, in <module>
    mimetypes.init()
  File "c:\Python27\lib\mimetypes.py", line 355, in init
    db.read_windows_registry()
  File "c:\Python27\lib\mimetypes.py", line 260, in read_windows_registry
    for ctype in enum_types(mimedb):
  File "c:\Python27\lib\mimetypes.py", line 250, in enum_types
    ctype = ctype.encode(default_encoding) # omit in 3.x!
UnicodeDecodeError: 'ascii' codec can't decode byte 0xe0 in position 0: ordinal not in range(128)

This can be reproduced, for example, on a Russian Windows XP installation which has QuickTime installed (QuickTime creates the non-Latin entries in the registry). The following line causes the exception to happen:

import mimetypes; mimetypes.init()

解决办法各种各样，下面说2个：

1. 修改mimetypes.py（有很多种修改办法，这里贴其中一种，添加如#<--标识的2行即可）

Alternative temporary solution
def enum_types(mimedb):
....
try:
  ctype = ctype.encode(default_encoding) # omit in 3.x!
except UnicodeEncodeError:
  pass
except Exception: #<--
  pass            #<--
else:
  yield ctype

或者：

2. 在Python安装目录下的Lib\site-packages文件夹创建sitecustomize.py文件，内容为：

import sys
sys.setdefaultencoding('cp936')

此外还可以清理注册表中HKEY_CLASSES_ROOT下所有非ascii字符的键。

不用费那劲了，直接下载修正的mimetypes.py覆盖原文件即可。

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完。