我在使用 Pylons 0.9.7 的 Mako 模板中经常遇到这个错误：
AttributeError: 'NoneType' object has no attribute 'decode'
通常我输入了一个不存在的变量名，尝试在代码行中使用 linbebreak，或者其他一些小错误。绝对是我的错。
这会导致浏览器中出现“内部服务器错误”，在调试视图中出现同样的情况，并且堆栈跟踪从 HTTPServer 开始并以 mako/exceptions.py 中的 AttributeError 结束。
我可以做些什么来使调试更容易，比如找出在 Mako 模板中生成异常的行？谢谢！
【问题讨论】：
我不确定这是否是同一个问题，但据我所知，当您执行 AJAX 加载页面片段时，这种情况经常发生。那么你不会得到比这条消息更有用的东西了。
但是，如果您尝试在浏览器中加载 AJAX 请求本身的地址（如果需要，将 post 参数替换为 get 参数），您将获得一个“正常”的调试页面。
【讨论】：
在我的例子中，我的模板中有一个除以 0 的错误。这导致了内部服务器错误，并且控制台输出中的堆栈跟踪非常无用。
我知道，听起来我不应该在模板中包含这种逻辑，但在这种情况下，我认为这样做是有道理的。这是我除以 0 得到的堆栈跟踪：
Exception happened during processing of request from ('127.0.0.1', 50681)
Traceback (most recent call last):
File "/Library/Python/2.6/site-packages/Paste-1.7.4-py2.6.egg/paste/httpserver.py", line 1068, in process_request_in_thread
self.finish_request(request, client_address)
File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/SocketServer.py", line 320, in finish_request
self.RequestHandlerClass(request, client_address, self)
File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/SocketServer.py", line 615, in __init__
self.handle()
File "/Library/Python/2.6/site-packages/Paste-1.7.4-py2.6.egg/paste/httpserver.py", line 442, in handle
BaseHTTPRequestHandler.handle(self)
File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/BaseHTTPServer.py", line 329, in handle
self.handle_one_request()
File "/Library/Python/2.6/site-packages/Paste-1.7.4-py2.6.egg/paste/httpserver.py", line 437, in handle_one_request
self.wsgi_execute()
File "/Library/Python/2.6/site-packages/Paste-1.7.4-py2.6.egg/paste/httpserver.py", line 287, in wsgi_execute
self.wsgi_start_response)
File "/Library/Python/2.6/site-packages/Paste-1.7.4-py2.6.egg/paste/cascade.py", line 130, in __call__
return self.apps[-1](environ, start_response)
File "/Library/Python/2.6/site-packages/Paste-1.7.4-py2.6.egg/paste/registry.py", line 375, in __call__
app_iter = self.application(environ, start_response)
File "/Library/Python/2.6/site-packages/Pylons-0.9.7-py2.6.egg/pylons/middleware.py", line 201, in __call__
self.app, environ, catch_exc_info=True)
File "/Library/Python/2.6/site-packages/Pylons-0.9.7-py2.6.egg/pylons/util.py", line 94, in call_wsgi_application
app_iter = application(environ, start_response)
File "/Library/Python/2.6/site-packages/WebError-0.10.2-py2.6.egg/weberror/evalexception.py", line 235, in __call__
return self.respond(environ, start_response)
File "/Library/Python/2.6/site-packages/WebError-0.10.2-py2.6.egg/weberror/evalexception.py", line 483, in respond
return debug_info.content()
File "/Library/Python/2.6/site-packages/WebError-0.10.2-py2.6.egg/weberror/evalexception.py", line 545, in content
result = tmpl_formatter(self.exc_value)
File "/Library/Python/2.6/site-packages/Pylons-0.9.7-py2.6.egg/pylons/error.py", line 43, in mako_html_data
css=False)
File "/Library/Python/2.6/site-packages/Mako-0.3.2-py2.6.egg/mako/template.py", line 189, in render
return runtime._render(self, self.callable_, args, data)
File "/Library/Python/2.6/site-packages/Mako-0.3.2-py2.6.egg/mako/runtime.py", line 403, in _render
_render_context(template, callable_, context, *args, **_kwargs_for_callable(callable_, data))
File "/Library/Python/2.6/site-packages/Mako-0.3.2-py2.6.egg/mako/runtime.py", line 434, in _render_context
_exec_template(inherit, lclcontext, args=args, kwargs=kwargs)
File "/Library/Python/2.6/site-packages/Mako-0.3.2-py2.6.egg/mako/runtime.py", line 457, in _exec_template
callable_(context, *args, **kwargs)
File "memory:0x1040470d0", line 54, in render_body
File "/Library/Python/2.6/site-packages/Mako-0.3.2-py2.6.egg/mako/exceptions.py", line 88, in __init__
self.records = self._init(traceback)
File "/Library/Python/2.6/site-packages/Mako-0.3.2-py2.6.egg/mako/exceptions.py", line 166, in _init
line = line.decode('ascii', 'replace')
AttributeError: 'NoneType' object has no attribute 'decode'
----------------------------------------
【讨论】：