Python Django Gunicorn:调用元类基时出错

我有一个Django应用程序，其中包括一个自定义模型字段（以及附带的表单字段）。当我使用内置的开发服务器运行项目时，它工作得很好。但是，使用gunicorn加载服务器会导致以下错误：

TemplateSyntaxError at /admin/
Caught TypeError while rendering: Error when calling the metaclass bases
    must be type, not None

为了完整起见，我将整个错误包括在下面，它显示了故障线路：

Traceback:
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/core/handlers/base.py" in get_response
  111.                         response = callback(request, *callback_args, **callback_kwargs)
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/contrib/admin/sites.py" in wrapper
  214.                 return self.admin_view(view, cacheable)(*args, **kwargs)
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/utils/decorators.py" in _wrapped_view
  93.                     response = view_func(request, *args, **kwargs)
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/views/decorators/cache.py" in _wrapped_view_func
  79.         response = view_func(request, *args, **kwargs)
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/contrib/admin/sites.py" in inner
  197.             return view(request, *args, **kwargs)
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/views/decorators/cache.py" in _wrapped_view_func
  79.         response = view_func(request, *args, **kwargs)
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/contrib/admin/sites.py" in index
  382.             context_instance=context_instance
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/shortcuts/__init__.py" in render_to_response
  20.     return HttpResponse(loader.render_to_string(*args, **kwargs), **httpresponse_kwargs)
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/template/loader.py" in render_to_string
  188.         return t.render(context_instance)
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/template/base.py" in render
  123.             return self._render(context)
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/template/base.py" in _render
  117.         return self.nodelist.render(context)
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/template/base.py" in render
  744.                 bits.append(self.render_node(node, context))
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/template/debug.py" in render_node
  73.             result = node.render(context)
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/template/loader_tags.py" in render
  127.         return compiled_parent._render(context)
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/template/base.py" in _render
  117.         return self.nodelist.render(context)
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/template/base.py" in render
  744.                 bits.append(self.render_node(node, context))
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/template/debug.py" in render_node
  73.             result = node.render(context)
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/template/loader_tags.py" in render
  127.         return compiled_parent._render(context)
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/template/base.py" in _render
  117.         return self.nodelist.render(context)
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/template/base.py" in render
  744.                 bits.append(self.render_node(node, context))
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/template/debug.py" in render_node
  73.             result = node.render(context)
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/template/defaulttags.py" in render
  311.             return self.nodelist_true.render(context)
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/template/base.py" in render
  744.                 bits.append(self.render_node(node, context))
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/template/debug.py" in render_node
  73.             result = node.render(context)
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/template/defaulttags.py" in render
  311.             return self.nodelist_true.render(context)
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/template/base.py" in render
  744.                 bits.append(self.render_node(node, context))
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/template/debug.py" in render_node
  73.             result = node.render(context)
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/template/loader_tags.py" in render
  64.             result = block.nodelist.render(context)
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/template/base.py" in render
  744.                 bits.append(self.render_node(node, context))
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/template/debug.py" in render_node
  73.             result = node.render(context)
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/template/defaulttags.py" in render
  437.             url = reverse(view_name, args=args, kwargs=kwargs, current_app=context.current_app)
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/core/urlresolvers.py" in reverse
  391.             *args, **kwargs)))
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/core/urlresolvers.py" in reverse
  312.         possibilities = self.reverse_dict.getlist(lookup_view)
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/core/urlresolvers.py" in _get_reverse_dict
  229.             self._populate()
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/core/urlresolvers.py" in _populate
  208.                     for name in pattern.reverse_dict:
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/core/urlresolvers.py" in _get_reverse_dict
  229.             self._populate()
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/core/urlresolvers.py" in _populate
  208.                     for name in pattern.reverse_dict:
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/core/urlresolvers.py" in _get_reverse_dict
  229.             self._populate()
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/core/urlresolvers.py" in _populate
  197.         for pattern in reversed(self.url_patterns):
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/core/urlresolvers.py" in _get_url_patterns
  279.         patterns = getattr(self.urlconf_module, "urlpatterns", self.urlconf_module)
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/core/urlresolvers.py" in _get_urlconf_module
  274.             self._urlconf_module = import_module(self.urlconf_name)
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/utils/importlib.py" in import_module
  35.     __import__(name)
File "/home/rob/projects/shipp/shipp/tickets/urls.py" in <module>
  3. from shipp.tickets.views import TicketListView, TicketDetailView, \
File "/home/rob/projects/shipp/shipp/tickets/views.py" in <module>
  15. from shipp.tickets.forms import TicketForm, TicketAttributesForm, \
File "/home/rob/projects/shipp/shipp/tickets/forms.py" in <module>
  26. class TicketTimeSpentForm(forms.ModelForm):
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/forms/models.py" in __new__
  205.                                       opts.exclude, opts.widgets, formfield_callback)
File "/home/rob/.virtualenvs/shipp/lib/python2.7/site-packages/django/forms/models.py" in fields_for_model
  159.             formfield = f.formfield(**kwargs)
File "/home/rob/projects/shipp/shipp/../shipp/tickets/fields.py" in formfield
  43.         return super(TimedeltaField, self).formfield(*args, **defaults)

Exception Type: TemplateSyntaxError at /admin/
Exception Value: Caught TypeError while rendering: Error when calling the metaclass bases
    must be type, not None

回溯：
get_响应中的文件“/home/rob/.virtualenvs/shipp/lib/python2.7/site packages/django/core/handlers/base.py”
111响应=回调（请求，*回调参数，**回调参数）
包装器中的文件“/home/rob/.virtualenvs/shipp/lib/python2.7/site packages/django/contrib/admin/sites.py”
214返回self.admin_视图（视图，可缓存）（*args，**kwargs）
视图中的文件“/home/rob/.virtualenvs/shipp/lib/python2.7/site packages/django/utils/decorators.py”
93响应=查看功能（请求，*args，**kwargs）
文件“/home/rob/.virtualenvs/shipp/lib/python2.7/site packages/django/views/decorators/cache.py”位于包装视图功能中
79响应=查看功能（请求，*args，**kwargs）
文件“/home/rob/.virtualenvs/shipp/lib/python2.7/site packages/django/contrib/admin/sites.py”
197返回视图（请求、*args、**kwargs）
文件“/home/rob/.virtualenvs/shipp/lib/python2.7/site packages/django/views/decorators/cache.py”位于包装视图功能中
79响应=查看功能（请求，*args，**kwargs）
索引中的文件“/home/rob/.virtualenvs/shipp/lib/python2.7/site packages/django/contrib/admin/sites.py”
382context\u实例=context\u实例
render\u to\u响应中的文件“/home/rob/.virtualenvs/shipp/lib/python2.7/site packages/django/shortcuts/\uuuuu init\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu
20返回HttpResponse（loader.render_to_string（*args，**kwargs），**HttpResponse_kwargs）
render_to_字符串中的文件“/home/rob/.virtualenvs/shipp/lib/python2.7/site packages/django/template/loader.py”
188返回t.render（上下文\实例）
render中的文件“/home/rob/.virtualenvs/shipp/lib/python2.7/site packages/django/template/base.py”
123返回self.\u呈现（上下文）
文件“/home/rob/.virtualenvs/shipp/lib/python2.7/site packages/django/template/base.py”位于_render中
117返回self.nodelist.render（上下文）
render中的文件“/home/rob/.virtualenvs/shipp/lib/python2.7/site packages/django/template/base.py”
744bits.append（self.render_节点（节点，上下文））
render_节点中的文件“/home/rob/.virtualenvs/shipp/lib/python2.7/site packages/django/template/debug.py”
73结果=node.render（上下文）
render中的文件“/home/rob/.virtualenvs/shipp/lib/python2.7/site packages/django/template/loader_tags.py”
127返回编译的\u父对象。\u呈现（上下文）
文件“/home/rob/.virtualenvs/shipp/lib/python2.7/site packages/django/template/base.py”位于_render中
117返回self.nodelist.render（上下文）
render中的文件“/home/rob/.virtualenvs/shipp/lib/python2.7/site packages/django/template/base.py”
744bits.append（self.render_节点（节点，上下文））
render_节点中的文件“/home/rob/.virtualenvs/shipp/lib/python2.7/site packages/django/template/debug.py”
73结果=node.render（上下文）
render中的文件“/home/rob/.virtualenvs/shipp/lib/python2.7/site packages/django/template/loader_tags.py”
127返回编译的\u父对象。\u呈现（上下文）
文件“/home/rob/.virtualenvs/shipp/lib/python2.7/site packages/django/template/base.py”位于_render中
117返回self.nodelist.render（上下文）
render中的文件“/home/rob/.virtualenvs/shipp/lib/python2.7/site packages/django/template/base.py”
744bits.append（self.render_节点（节点，上下文））
render_节点中的文件“/home/rob/.virtualenvs/shipp/lib/python2.7/site packages/django/template/debug.py”
73结果=node.render（上下文）
render中的文件“/home/rob/.virtualenvs/shipp/lib/python2.7/site packages/django/template/defaulttags.py”
311返回self.nodelist\u true.render（上下文）
render中的文件“/home/rob/.virtualenvs/shipp/lib/python2.7/site packages/django/template/base.py”
744bits.append（self.render_节点（节点，上下文））
render_节点中的文件“/home/rob/.virtualenvs/shipp/lib/python2.7/site packages/django/template/debug.py”
73结果=node.render（上下文）
render中的文件“/home/rob/.virtualenvs/shipp/lib/python2.7/site packages/django/template/defaulttags.py”
311返回self.nodelist\u true.render（上下文）
render中的文件“/home/rob/.virtualenvs/shipp/lib/python2.7/site packages/django/template/base.py”
744bits.append（self.render_节点（节点，上下文））
render_节点中的文件“/home/rob/.virtualenvs/shipp/lib/python2.7/site packages/django/template/debug.py”
73结果=node.render（上下文）
render中的文件“/home/rob/.virtualenvs/shipp/lib/python2.7/site packages/django/template/loader_tags.py”
64结果=block.nodelist.render（上下文）
render中的文件“/home/rob/.virtualenvs/shipp/lib/python2.7/site packages/django/template/base.py”
744bits.append（self.render_节点（节点，上下文））
render_节点中的文件“/home/rob/.virtualenvs/shipp/lib/python2.7/site packages/django/template/debug.py”
73结果=node.render（上下文）
render中的文件“/home/rob/.virtualenvs/shipp/lib/python2.7/site packages/django/template/defaulttags.py”
437url=reverse（查看\名称，args=args，kwargs=kwargs，当前\应用程序=上下文。当前\应用程序）
文件“/home/rob/.virtualenvs/shipp/lib/python2.7/site packages/django/core/urlresolvers.py”的格式相反
391.             *args，**kwargs）））
文件“/home/rob/.virtualenvs/shipp/lib/python2.7/site packages/django/core/urlresolvers.py”的格式相反
312可能性=self.reverse\u dict.getlist（查找视图）
文件“/home/rob/.virtualenvs/shipp/lib/python2.7/site packages/django/core/urlresolvers.py”位于
229