Ist es möglich, Vorlagen-Tags in Django 1.11 zu verwenden, um einen "NoneType" -Fehler zu umgehen?

Question

Ich verwende Schablonen-Tags, um Daten darzustellen, die von Klassenobjekten am Back-End abgeleitet wurden. Beide Klassenobjekte erfordern Eingaben vom Benutzer, um zu arbeiten, und wenn die Eingabe nicht gültig ist, geben sie None zurück.

Ich muss eine Differenzberechnung von zwei der Objekte auf der Seite (es muss nicht in der Datenbank gespeichert werden). Also habe ich mathfilters https://pypi.python.org/pypi/django-mathfilters installiert, um die Subtraktion zu machen, die funktionierte, wenn es Benutzereingaben gibt, aber nicht funktioniert, wenn ich gerade zur Seite oder keiner Benutzereingabe navigiere.

Vorlage 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> 

Welche mir diesen Fehler gibt:

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' 

ich diese Filter versucht:

<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> 

den gleichen Fehler empfangen.

Gibt es einen Weg mit Vorlage Tags und Filtern, um dieses Problem zu beheben?

Answer 1

Scheint, dass "int_goals" nicht definiert ist, also keine. Wenn Sie versuchen, eine mathematische Operation auf int_numbers.get_sum_int_daily_numbers - None.get_div_goalsint_wdaysint_numbers.get_sum_int_daily_numbers - None.get_div_goalsint_wdays zu tun, wirft eine Ausnahme