解决django使用logging时“character mapping must return integer, None or unicode”错误
今天调试Django项目时候，使用Logging记录异常并发送邮件给网站管理人员，测试时候始终报错：
Traceback (most recent call last):
File "/usr/lib64/python2.7/wsgiref/handlers.py", line 85, in run
self.result = application(self.environ, self.start_response)
File "/home/xsy/.virtualenvs/dz_pro/lib/python2.7/site-packages/django/core/handlers/wsgi.py", line 177, in __call__
response = self.get_response(request)
File "/home/xsy/.virtualenvs/dz_pro/lib/python2.7/site-packages/django/core/handlers/base.py", line 230, in get_response
response = self.handle_uncaught_exception(request, resolver, sys.exc_info())
File "/home/xsy/.virtualenvs/dz_pro/lib/python2.7/site-packages/django/core/handlers/base.py", line 284, in handle_uncaught_exception
'request': request
File "/usr/lib64/python2.7/logging/__init__.py", line 1185, in error
self._log(ERROR, msg, args, **kwargs)
File "/usr/lib64/python2.7/logging/__init__.py", line 1278, in _log
self.handle(record)
File "/usr/lib64/python2.7/logging/__init__.py", line 1288, in handle
self.callHandlers(record)
File "/usr/lib64/python2.7/logging/__init__.py", line 1328, in callHandlers
hdlr.handle(record)
File "/usr/lib64/python2.7/logging/__init__.py", line 751, in handle
self.emit(record)
File "/home/xsy/.virtualenvs/dz_pro/lib/python2.7/site-packages/django/utils/log.py", line 117, in emit
self.send_mail(subject, message, fail_silently=True, html_message=html_message)
File "/home/xsy/.virtualenvs/dz_pro/lib/python2.7/site-packages/django/utils/log.py", line 120, in send_mail
mail.mail_admins(subject, message, *args, connection=self.connection(), **kwargs)
File "/home/xsy/.virtualenvs/dz_pro/lib/python2.7/site-packages/django/core/mail/__init__.py", line 97, in mail_admins
mail.send(fail_silently=fail_silently)
File "/home/xsy/.virtualenvs/dz_pro/lib/python2.7/site-packages/django/core/mail/message.py", line 292, in send
return self.get_connection(fail_silently).send_messages([self])
File "/home/xsy/.virtualenvs/dz_pro/lib/python2.7/site-packages/django/core/mail/backends/smtp.py", line 100, in send_messages
new_conn_created = self.open()
File "/home/xsy/.virtualenvs/dz_pro/lib/python2.7/site-packages/django/core/mail/backends/smtp.py", line 67, in open
self.connection.login(self.username, self.password)
File "/usr/lib64/python2.7/smtplib.py", line 607, in login
(code, resp) = self.docmd(encode_cram_md5(resp, user, password))
File "/usr/lib64/python2.7/smtplib.py", line 571, in encode_cram_md5
response = user + " " + hmac.HMAC(password, challenge).hexdigest()
File "/usr/lib64/python2.7/hmac.py", line 78, in __init__
self.outer.update(key.translate(trans_5C))
TypeError: character mapping must return integer, None or unicode
根据错误提示，追进了hmac.py中看了源码，发现key其实就是一个字符串，是配置在settings中的EMAIL_HOST_USER以及EMAIL_HOST_PASSWORD，而translate函数则是根据给出的参数表将字符串进行映射加密的，而且是最简单的凯撒加密法。
这里看了半天也看不出问题在哪，纠结了好久后猛然发现问题的关键出自settings.py:
from __future__ import absolute_import, unicode_literals
...
EMAIL_HOST = 'mail.xxx.com'
EMAIL_HOST_USER = 'xxxx'
EMAIL_HOST_PASSWORD = b'xxxx' # or str('xxx')
...
就是因为引入了unicode_literals，默认字符都变成了unicode而不是py2的str了（如果你还没被py2中的str和unicode坑过，我只能恭喜你了）所以如果想使用str类型则需要使用’b'显示声明或者使用str函数进行转换。
这个__future__本意是让py2能够使用一些py3中的新特性，方便进行版本迁移的。比如在py2中默认除法是“地板除”，即只保留整数位；而py3中则变成了“精确除”，这种情况下我们可以引用division来保持语法一至：
from __future__ import division
print '10 / 3 =', 10 / 3
print '10.0 / 3 =', 10.0 / 3
print '10 // 3 =', 10 // 3
结果：
10 / 3 = 3.33333333333
10.0 / 3 = 3.33333333333
10 // 3 = 3
再比如absolute_import则是禁用隐式相对引用(implicit relative import）的，因为官方不推荐这种引用方式了已经。
最后打个广告：cookiecutter-simple-django-cn 是我写的一个生成django基础框架的程序，参考了cookiecutter-django移除修改了一些国内不好用的选项，欢迎各位试用并提供宝贵意见～
