Django無法連接'str'和'NoneType'對象

Question

我在嘗試生成事件模型報告時遇到此錯誤，此行爲{{ event.reports_dump | safe }}tmpls.append("<span>"+event.human_date_range()+"</span>")它使用創建的自定義函數來創建可讀文本。

我試圖通過第一返回字符串「無」來解決問題，而不是什麼

def human_date_range(self): 
    ... 
    if not (starts and ends): 
     #from return to return "None" 
     return "None" 

但遷移和重新啓動服務器後持續存在的錯誤。我可以告訴的變化已經生效從錯誤日誌，所以我overrided全功能，但它仍然返回相同的錯誤

def human_date_range(self): 
    ... 
    return "None" 
    if not (starts and ends): 
     #from return to return "None" 
     return "None" 

需要一些幫助調試它。

我貼你會使用字符串插值，這需要照顧的事情是這樣的更好的錯誤日誌和模型

class Event(BaseItemModel, AdminURLMixin): 
    venue = models.ForeignKey(Venue) 
    categories = TreeManyToManyField(Category) 

    parent = models.ForeignKey('Event', blank=True, verbose_name='Parent Event', null=True,) 

    contact_person = models.CharField(max_length=255, blank=True,) 
    contact_email = models.EmailField(max_length=255, blank=True, help_text='Only one valid email address allowed') 
    contact_phone = models.CharField(max_length=255, blank=True,) 
    contact_website = models.URLField(max_length=255, blank=True, help_text='Only one valid web address allowed. Must include http:// or https://') 
    contact_address = models.TextField(blank=True,) 

    free = models.BooleanField(default=False) 
    taxi = models.NullBooleanField(default=None) 
    jkia_ad = models.NullBooleanField(default=None) 
    cost = models.PositiveIntegerField(blank=True, null=True, verbose_name="Cost in KES", default=0, help_text='Only numbers allowed, if price is not in KES convert the amount to KES and write the Currency and Cost in Cost Description') 
    cost_desc = models.TextField(blank=True, verbose_name='Cost description', help_text='If several prices available write them here using the regular price in Cost') 

    artist = models.TextField(blank=True,) 
    event_ticket = models.IntegerField(blank=True, null=True) 

    num_days = models.IntegerField(default=0, editable=False, db_index=True,) 

    old_dates = models.TextField(blank=True, editable=False,) 


    def human_date_range(self): 

     starts = self.starts_datetime() 
     ends = self.ends_datetime() 

     return "None" 

     if not (starts and ends): 
      return "None" 

     if starts.date() == ends.date(): 
      # February 21st, 10pm 
      return starts.strftime('%B ')+humanize.ordinal(int(starts.strftime('%d')))+', '+str(int(starts.strftime('%I')))+starts.strftime('%p').lower() 

     elif starts.year == ends.year and starts.month == ends.month: 
      # February 21st, 10pm-11pm 
      return\ 
       starts.strftime('%B ')+humanize.ordinal(int(starts.strftime('%d')))+', '+\ 
       str(int(starts.strftime('%I')))+starts.strftime('%p').lower()+' - '+str(int(ends.strftime('%I')))+ends.strftime('%p').lower() 

     elif starts.year == ends.year: 
      # February 21st - March 23rd, 10pm-11pm 
      return\ 
       starts.strftime('%B ')+humanize.ordinal(int(starts.strftime('%d')))+' - '+ends.strftime('%B ')+humanize.ordinal(int(ends.strftime('%d')))+', '+\ 
       str(int(starts.strftime('%I')))+starts.strftime('%p').lower()+' - '+str(int(ends.strftime('%I')))+ends.strftime('%p').lower() 

     else: 
      # February 21st 2013 - March 4th 2014, 10pm-11pm 
      return starts.strftime('%B ')+humanize.ordinal(int(starts.strftime('%d')))+starts.strftime(' %Y')+' - '+ends.strftime('%B ')+humanize.ordinal(int(ends.strftime('%d')))+ends.strftime(' %Y')+', '+\ 
      str(int(starts.strftime('%I')))+starts.strftime('%p').lower()+' - '+str(int(ends.strftime('%I')))+ends.strftime('%p').lower() 

錯誤日誌

Environment: 

Request Method: GET 
Request URL: http://stage.kenyabuzz.com/admin/reports/events/2015-12-8-0-0/2015-12-14-0-0/ 

Django Version: 1.7.10 
Python Version: 2.7.5 


Template error: 
In template /home/kbuzz/webapps/kenyabuzz/kb/reports/templates/reports/report.html, error at line 71 
    cannot concatenate 'str' and 'NoneType' objects 
    61 : 
    62 :  <div> 
    63 :   {% for event in stat.v %} 
    64 :   
    65 :   <div class='event'> 
    66 : 
    67 :   {% if event.title %} 
    68 :   <span class='bold'>{{ event.title }}: </span> 
    69 :   {% endif %} 
    70 : 
    71 :   {{ event.reports_dump | safe }} 
    72 : 
    73 :   {% if event.description %} 
    74 :   <span>{{ event.description }}</span> 
    75 :   {% endif %} 
    76 : 
    77 :   </div> 
    78 : 
    79 :   {% endfor %} 
    80 : 
    81 :  </div> 


Traceback: 
File "/home/kbuzz/webapps/kenyabuzz/lib/python2.7/Django-1.7.10-py2.7.egg/django/core/handlers/base.py" in get_response 
    111.      response = wrapped_callback(request, *callback_args, **callback_kwargs) 
File "/home/kbuzz/webapps/kenyabuzz/lib/python2.7/Django-1.7.10-py2.7.egg/django/contrib/auth/decorators.py" in _wrapped_view 
    21.     return view_func(request, *args, **kwargs) 
File "/home/kbuzz/webapps/kenyabuzz/kb/reports/views.py" in events 
    205.   RequestContext(request, {}) 
File "/home/kbuzz/webapps/kenyabuzz/lib/python2.7/Django-1.7.10-py2.7.egg/django/shortcuts.py" in render_to_response 
    25.  return HttpResponse(loader.render_to_string(*args, **kwargs), **httpresponse_kwargs) 
File "/home/kbuzz/webapps/kenyabuzz/lib/python2.7/Django-1.7.10-py2.7.egg/django/template/loader.py" in render_to_string 
    178.   return t.render(context_instance) 
File "/home/kbuzz/webapps/kenyabuzz/lib/python2.7/Django-1.7.10-py2.7.egg/django/template/base.py" in render 
    148.    return self._render(context) 
File "/home/kbuzz/webapps/kenyabuzz/lib/python2.7/Django-1.7.10-py2.7.egg/django/template/base.py" in _render 
    142.   return self.nodelist.render(context) 
File "/home/kbuzz/webapps/kenyabuzz/lib/python2.7/Django-1.7.10-py2.7.egg/django/template/base.py" in render 
    844.     bit = self.render_node(node, context) 
File "/home/kbuzz/webapps/kenyabuzz/lib/python2.7/Django-1.7.10-py2.7.egg/django/template/debug.py" in render_node 
    80.    return node.render(context) 
File "/home/kbuzz/webapps/kenyabuzz/lib/python2.7/Django-1.7.10-py2.7.egg/django/template/loader_tags.py" in render 
    126.   return compiled_parent._render(context) 
File "/home/kbuzz/webapps/kenyabuzz/lib/python2.7/Django-1.7.10-py2.7.egg/django/template/base.py" in _render 
    142.   return self.nodelist.render(context) 
File "/home/kbuzz/webapps/kenyabuzz/lib/python2.7/Django-1.7.10-py2.7.egg/django/template/base.py" in render 
    844.     bit = self.render_node(node, context) 
File "/home/kbuzz/webapps/kenyabuzz/lib/python2.7/Django-1.7.10-py2.7.egg/django/template/debug.py" in render_node 
    80.    return node.render(context) 
File "/home/kbuzz/webapps/kenyabuzz/lib/python2.7/Django-1.7.10-py2.7.egg/django/template/loader_tags.py" in render 
    126.   return compiled_parent._render(context) 
File "/home/kbuzz/webapps/kenyabuzz/lib/python2.7/Django-1.7.10-py2.7.egg/django/template/base.py" in _render 
    142.   return self.nodelist.render(context) 
File "/home/kbuzz/webapps/kenyabuzz/lib/python2.7/Django-1.7.10-py2.7.egg/django/template/base.py" in render 
    844.     bit = self.render_node(node, context) 
File "/home/kbuzz/webapps/kenyabuzz/lib/python2.7/Django-1.7.10-py2.7.egg/django/template/debug.py" in render_node 
    80.    return node.render(context) 
File "/home/kbuzz/webapps/kenyabuzz/lib/python2.7/Django-1.7.10-py2.7.egg/django/template/loader_tags.py" in render 
    65.     result = block.nodelist.render(context) 
File "/home/kbuzz/webapps/kenyabuzz/lib/python2.7/Django-1.7.10-py2.7.egg/django/template/base.py" in render 
    844.     bit = self.render_node(node, context) 
File "/home/kbuzz/webapps/kenyabuzz/lib/python2.7/Django-1.7.10-py2.7.egg/django/template/debug.py" in render_node 
    80.    return node.render(context) 
File "/home/kbuzz/webapps/kenyabuzz/lib/python2.7/Django-1.7.10-py2.7.egg/django/template/defaulttags.py" in render 
    201.        nodelist.append(node.render(context)) 
File "/home/kbuzz/webapps/kenyabuzz/lib/python2.7/Django-1.7.10-py2.7.egg/django/template/defaulttags.py" in render 
    201.        nodelist.append(node.render(context)) 
File "/home/kbuzz/webapps/kenyabuzz/lib/python2.7/Django-1.7.10-py2.7.egg/django/template/debug.py" in render 
    90.    output = self.filter_expression.resolve(context) 
File "/home/kbuzz/webapps/kenyabuzz/lib/python2.7/Django-1.7.10-py2.7.egg/django/template/base.py" in resolve 
    596.     obj = self.var.resolve(context) 
File "/home/kbuzz/webapps/kenyabuzz/lib/python2.7/Django-1.7.10-py2.7.egg/django/template/base.py" in resolve 
    734.    value = self._resolve_lookup(context) 
File "/home/kbuzz/webapps/kenyabuzz/lib/python2.7/Django-1.7.10-py2.7.egg/django/template/base.py" in _resolve_lookup 
    788.        current = current() 
File "/home/kbuzz/webapps/kenyabuzz/kb/events/models.py" in reports_dump 
    175.   tmpls.append("<span>"+event.human_date_range()+"</span>") 

Exception Type: TypeError at /admin/reports/events/2015-12-8-0-0/2015-12-14-0-0/ 
Exception Value: cannot concatenate 'str' and 'NoneType' objects 

Answer 1

。

tmpls.append("<span>{}</span>".format(event.human_date_range()))