可以在Django 1.11中使用模板标记来绕过“NoneType”错误吗?

我使用模板标记来表示从后端的类对象派生的数据。这两个类对象都需要用户的输入才能工作,如果输入无效,则返回None。

https://pypi.python.org/pypi/django-mathfilters 如果有用户输入,则执行减法,但如果我只是导航到页面或没有用户输入,则执行减法不起作用。

模板HTML:

<tr>
   <td>Interest</td>
   <td class="data">${{int_numbers.get_sum_int_daily_numbers  | intcomma }}</td>
   <td class="data">${{int_goals.get_div_goalsint_wdays | intcomma }}</td>
   <td class="data"><font class="red">
    ${{ int_numbers.get_sum_int_daily_numbers|sub:int_goals.get_div_goalsint_wdays | intcomma }}
                </font>
   </td>
</tr>

这给了我一个错误:

Traceback:

File "C:\pycharm-virtenv\DjangoPostgres\lib\site-packages\django\template\base.py" in _resolve_lookup
  882.                     current = current[bit]

During handling of the above exception ('NoneType' object is not subscriptable), another exception occurred:

File "C:\pycharm-virtenv\DjangoPostgres\lib\site-packages\django\template\base.py" in _resolve_lookup
  890.                         current = getattr(current, bit)

During handling of the above exception ('NoneType' object has no attribute 'get_div_goalsint_wdays'), another exception occurred:

File "C:\pycharm-virtenv\DjangoPostgres\lib\site-packages\django\template\base.py" in _resolve_lookup
  896.                             current = current[int(bit)]

During handling of the above exception (invalid literal for int() with base 10: 'get_div_goalsint_wdays'), another exception occurred:

File "C:\pycharm-virtenv\DjangoPostgres\lib\site-packages\django\core\handlers\exception.py" in inner
  41.             response = get_response(request)

File "C:\pycharm-virtenv\DjangoPostgres\lib\site-packages\django\core\handlers\base.py" in _get_response
  187.                 response = self.process_exception_by_middleware(e, request)

File "C:\pycharm-virtenv\DjangoPostgres\lib\site-packages\django\core\handlers\base.py" in _get_response
  185.                 response = wrapped_callback(request, *callback_args, **callback_kwargs)

File "C:\DevProj\am\amreports\reports\views.py" in goals_view
  61.         'int_monthtodate': int_monthtodate_goals,

File "C:\pycharm-virtenv\DjangoPostgres\lib\site-packages\django\shortcuts.py" in render
  30.     content = loader.render_to_string(template_name, context, request, using=using)

File "C:\pycharm-virtenv\DjangoPostgres\lib\site-packages\django\template\loader.py" in render_to_string
  68.     return template.render(context, request)

File "C:\pycharm-virtenv\DjangoPostgres\lib\site-packages\django\template\backends\django.py" in render
  66.             return self.template.render(context)

File "C:\pycharm-virtenv\DjangoPostgres\lib\site-packages\django\template\base.py" in render
  207.                     return self._render(context)

File "C:\pycharm-virtenv\DjangoPostgres\lib\site-packages\django\template\base.py" in _render
  199.         return self.nodelist.render(context)

File "C:\pycharm-virtenv\DjangoPostgres\lib\site-packages\django\template\base.py" in render
  990.                 bit = node.render_annotated(context)

File "C:\pycharm-virtenv\DjangoPostgres\lib\site-packages\django\template\base.py" in render_annotated
  957.             return self.render(context)

File "C:\pycharm-virtenv\DjangoPostgres\lib\site-packages\django\template\loader_tags.py" in render
  177.             return compiled_parent._render(context)

File "C:\pycharm-virtenv\DjangoPostgres\lib\site-packages\django\template\base.py" in _render
  199.         return self.nodelist.render(context)

File "C:\pycharm-virtenv\DjangoPostgres\lib\site-packages\django\template\base.py" in render
  990.                 bit = node.render_annotated(context)

File "C:\pycharm-virtenv\DjangoPostgres\lib\site-packages\django\template\base.py" in render_annotated
  957.             return self.render(context)

File "C:\pycharm-virtenv\DjangoPostgres\lib\site-packages\django\template\loader_tags.py" in render
  72.                 result = block.nodelist.render(context)

File "C:\pycharm-virtenv\DjangoPostgres\lib\site-packages\django\template\base.py" in render
  990.                 bit = node.render_annotated(context)

File "C:\pycharm-virtenv\DjangoPostgres\lib\site-packages\django\template\base.py" in render_annotated
  957.             return self.render(context)

File "C:\pycharm-virtenv\DjangoPostgres\lib\site-packages\django\template\base.py" in render
  1040.             output = self.filter_expression.resolve(context)

File "C:\pycharm-virtenv\DjangoPostgres\lib\site-packages\django\template\base.py" in resolve
  730.                     arg_vals.append(arg.resolve(context))

File "C:\pycharm-virtenv\DjangoPostgres\lib\site-packages\django\template\base.py" in resolve
  849.             value = self._resolve_lookup(context)

File "C:\pycharm-virtenv\DjangoPostgres\lib\site-packages\django\template\base.py" in _resolve_lookup
  903.                                                        (bit, current))  # missing attribute

Exception Type: VariableDoesNotExist at /reports/goals/
Exception Value: Failed lookup for key [get_div_goalsint_wdays] in 'None'

我试过这个过滤器:

<tr>
   <td>Interest</td>
   <td class="data">${{int_numbers.get_sum_int_daily_numbers  | intcomma }}</td>
   <td class="data">${{int_goals.get_div_goalsint_wdays | intcomma }}</td>                  
    <td class="data"><font class="red">
        {% if int_numbers.get_sum_int_daily_numbers|sub:int_goals.get_div_goalsint_wdays is "None" %}
        0
        {% else %}
        ${{ int_numbers.get_sum_int_daily_numbers|sub:int_goals.get_div_goalsint_wdays | intcomma }}
         {% endif %}
                    </font>
    </td>
</tr>

收到相同的错误。

有没有办法用模板标签和过滤器来纠正这个问题?