强制转换为 Unicode：需要字符串或缓冲区，在 django admin 中渲染时发现 NoneType

Posted 2023-02-24

【中文标题】强制转换为 Unicode：需要字符串或缓冲区，在 django admin 中渲染时发现 NoneType

【英文标题】：coercing to Unicode: need string or buffer, NoneType found when rendering in django admin

【发布时间】：2013-04-16 15:34:46

【问题描述】：

这个错误我很久没解决了：

渲染时捕获 TypeError：强制转换为 Unicode：需要字符串或缓冲区，找到 NoneType

当我尝试在我的一个模型上添加或修改时，它会在管理员中发生（显示正常）

这是模型：

class PS(models.Model):
    id_ps = models.IntegerField(null=True)
    client = models.ForeignKey(Client, null=True, blank=True)
    nom_du_site = models.CharField(max_length=250)
    rue_livraison = models.TextField(null=True)
    complement_adresse = models.TextField(null=True)
    code_postal_livraison = models.CharField(max_length=50, null=True)
    ville_livraison = models.CharField(max_length=200, null=True)
    pays_livraison = models.CharField(max_length=200, null=True)
    distributeur = models.CharField(max_length=50, null=True)
    tarif = models.CharField(max_length=250, null=True)
    type_tarif = models.CharField(max_length=50, null=True)
    type_installation = models.CharField(max_length=50, null=True)

    def __unicode__(self):
        return self.nom_du_site

    @property
    def pce(self):        
        try:
            return PCE.objects.filter(ps=self)[0]
        except IndexError:
            return
    #    
    def get_pce(self):
        from pce.models import PCE
        return PCE.objects.filter(ps=self).exclude(frequence='6M')
    #
    def get_pce_6m(self):
        from pce.models import PCE
        return PCE.objects.filter(ps=self,frequence='6M') 

知道我在这里做错了什么吗？

追溯：

    Environment:

    Request Method: GET
    Request URL: http://127.0.0.1:8026/admin/ps/ps/add/
    Django Version: 1.2.5
    Python Version: 2.7.2
    Installed Applications:
    ['django.contrib.auth',
     'django.contrib.contenttypes',
     'django.contrib.sessions',
     'django.contrib.sites',
     'django.contrib.messages',
     'django.contrib.admin',
     'easy_thumbnails',
     'django_extensions',
     'contentadmin',
     'south',
     'sentry',
     'sentry.client',
     'indexer',
     'file_uploader',
     'paging',
     'pagination',
     'consommation',
     'ps',
     'pce',
     'profil',
     'analytics',
     'document']
    Installed Middleware:
    ('annoying.middlewares.StaticServe',
     'django.middleware.common.CommonMiddleware',
     'django.contrib.sessions.middleware.SessionMiddleware',
     'django.middleware.csrf.CsrfViewMiddleware',
     'django.contrib.auth.middleware.AuthenticationMiddleware',
     'django.contrib.messages.middleware.MessageMiddleware',
     'pagination.middleware.PaginationMiddleware')


    Template error:
    In template /usr/local/lib/python2.7/dist-packages/django/contrib/admin/templates/admin/includes/fieldset.html, error at line 19
       Caught TypeError while rendering: coercing to Unicode: need string or buffer, NoneType found
       9 :             % for field in line %


       10 :                 <div% if not line.fields|length_is:'1' % class="field-box% if not field.is_readonly and field.errors % errors% endif %"% endif %>


       11 :                     % if not line.fields|length_is:'1' and not field.is_readonly % field.errors % endif %


       12 :                     % if field.is_checkbox %


       13 :                          field.field  field.label_tag 


       14 :                     % else %


       15 :                          field.label_tag 


       16 :                         % if field.is_readonly %


       17 :                             <p> field.contents </p>


       18 :                         % else %


       19 :                               field.field  


       20 :                         % endif %


       21 :                     % endif %


       22 :                     % if field.field.field.help_text %


       23 :                         <p class="help"> field.field.field.help_text|safe </p>


       24 :                     % endif %


       25 :                 </div>


       26 :             % endfor %


       27 :         </div>


       28 :     % endfor %


       29 : </fieldset>


    Traceback:
    File "/usr/local/lib/python2.7/dist-packages/django/core/handlers/base.py" in get_response
      100.                     response = callback(request, *callback_args, **callback_kwargs)
    File "/usr/local/lib/python2.7/dist-packages/django/contrib/admin/options.py" in wrapper
      288.                 return self.admin_site.admin_view(view)(*args, **kwargs)
    File "/usr/local/lib/python2.7/dist-packages/django/utils/decorators.py" in _wrapped_view
      76.                     response = view_func(request, *args, **kwargs)
    File "/usr/local/lib/python2.7/dist-packages/django/views/decorators/cache.py" in _wrapped_view_func
      78.         response = view_func(request, *args, **kwargs)
    File "/usr/local/lib/python2.7/dist-packages/django/contrib/admin/sites.py" in inner
      190.             return view(request, *args, **kwargs)
    File "/usr/local/lib/python2.7/dist-packages/django/utils/decorators.py" in _wrapper
      21.             return decorator(bound_func)(*args, **kwargs)
    File "/usr/local/lib/python2.7/dist-packages/django/utils/decorators.py" in _wrapped_view
      76.                     response = view_func(request, *args, **kwargs)
    File "/usr/local/lib/python2.7/dist-packages/django/utils/decorators.py" in bound_func
      17.                 return func(self, *args2, **kwargs2)
    File "/usr/local/lib/python2.7/dist-packages/django/db/transaction.py" in _commit_on_success
      299.                     res = func(*args, **kw)
    File "/usr/local/lib/python2.7/dist-packages/django/contrib/admin/options.py" in add_view
      909.         return self.render_change_form(request, context, form_url=form_url, add=True)
    File "/usr/local/lib/python2.7/dist-packages/django/contrib/admin/options.py" in render_change_form
      692.         ], context, context_instance=context_instance)
    File "/usr/local/lib/python2.7/dist-packages/django/shortcuts/__init__.py" in render_to_response
      20.     return HttpResponse(loader.render_to_string(*args, **kwargs), **httpresponse_kwargs)
    File "/usr/local/lib/python2.7/dist-packages/django/template/loader.py" in render_to_string
      186.     return t.render(context_instance)
    File "/usr/local/lib/python2.7/dist-packages/django/template/__init__.py" in render
      173.             return self._render(context)
    File "/usr/local/lib/python2.7/dist-packages/django/template/__init__.py" in _render
      167.         return self.nodelist.render(context)
    File "/usr/local/lib/python2.7/dist-packages/django/template/__init__.py" in render
      796.                 bits.append(self.render_node(node, context))
    File "/usr/local/lib/python2.7/dist-packages/django/template/debug.py" in render_node
      72.             result = node.render(context)
    File "/usr/local/lib/python2.7/dist-packages/django/template/loader_tags.py" in render
      125.         return compiled_parent._render(context)
    File "/usr/local/lib/python2.7/dist-packages/django/template/__init__.py" in _render
      167.         return self.nodelist.render(context)
    File "/usr/local/lib/python2.7/dist-packages/django/template/__init__.py" in render
      796.                 bits.append(self.render_node(node, context))
    File "/usr/local/lib/python2.7/dist-packages/django/template/debug.py" in render_node
      72.             result = node.render(context)
    File "/usr/local/lib/python2.7/dist-packages/django/template/loader_tags.py" in render
      125.         return compiled_parent._render(context)
    File "/usr/local/lib/python2.7/dist-packages/django/template/__init__.py" in _render
      167.         return self.nodelist.render(context)
    File "/usr/local/lib/python2.7/dist-packages/django/template/__init__.py" in render
      796.                 bits.append(self.render_node(node, context))
    File "/usr/local/lib/python2.7/dist-packages/django/template/debug.py" in render_node
      72.             result = node.render(context)
    File "/usr/local/lib/python2.7/dist-packages/django/template/loader_tags.py" in render
      62.             result = block.nodelist.render(context)
    File "/usr/local/lib/python2.7/dist-packages/django/template/__init__.py" in render
      796.                 bits.append(self.render_node(node, context))
    File "/usr/local/lib/python2.7/dist-packages/django/template/debug.py" in render_node
      72.             result = node.render(context)
    File "/usr/local/lib/python2.7/dist-packages/django/template/defaulttags.py" in render
      174.                 nodelist.append(node.render(context))
    File "/usr/local/lib/python2.7/dist-packages/django/template/loader_tags.py" in render
      139.             return self.template.render(context)
    File "/usr/local/lib/python2.7/dist-packages/django/template/__init__.py" in render
      173.             return self._render(context)
    File "/usr/local/lib/python2.7/dist-packages/django/template/__init__.py" in _render
      167.         return self.nodelist.render(context)
    File "/usr/local/lib/python2.7/dist-packages/django/template/__init__.py" in render
      796.                 bits.append(self.render_node(node, context))
    File "/usr/local/lib/python2.7/dist-packages/django/template/debug.py" in render_node
      72.             result = node.render(context)
    File "/usr/local/lib/python2.7/dist-packages/django/template/defaulttags.py" in render
      174.                 nodelist.append(node.render(context))
    File "/usr/local/lib/python2.7/dist-packages/django/template/defaulttags.py" in render
      174.                 nodelist.append(node.render(context))
    File "/usr/local/lib/python2.7/dist-packages/django/template/defaulttags.py" in render
      260.             return self.nodelist_false.render(context)
    File "/usr/local/lib/python2.7/dist-packages/django/template/__init__.py" in render
      796.                 bits.append(self.render_node(node, context))
    File "/usr/local/lib/python2.7/dist-packages/django/template/debug.py" in render_node
      72.             result = node.render(context)
    File "/usr/local/lib/python2.7/dist-packages/django/template/defaulttags.py" in render
      260.             return self.nodelist_false.render(context)
    File "/usr/local/lib/python2.7/dist-packages/django/template/__init__.py" in render
      796.                 bits.append(self.render_node(node, context))
    File "/usr/local/lib/python2.7/dist-packages/django/template/debug.py" in render_node
      72.             result = node.render(context)
    File "/usr/local/lib/python2.7/dist-packages/django/template/debug.py" in render
      91.             output = force_unicode(output)
    File "/usr/local/lib/python2.7/dist-packages/django/utils/encoding.py" in force_unicode
      66.                 s = unicode(s)
    File "/usr/local/lib/python2.7/dist-packages/django/forms/forms.py" in __unicode__
      408.         return self.as_widget()
    File "/usr/local/lib/python2.7/dist-packages/django/forms/forms.py" in as_widget
      450.         return widget.render(name, data, attrs=attrs)
    File "/usr/local/lib/python2.7/dist-packages/django/contrib/admin/widgets.py" in render
      247.         output = [self.widget.render(name, value, *args, **kwargs)]
    File "/usr/local/lib/python2.7/dist-packages/django/forms/widgets.py" in render
      447.         options = self.render_options(choices, [value])
    File "/usr/local/lib/python2.7/dist-packages/django/forms/widgets.py" in render_options
      464.         for option_value, option_label in chain(self.choices, choices):
    File "/usr/local/lib/python2.7/dist-packages/django/forms/models.py" in __iter__
      898.                 yield self.choice(obj)
    File "/usr/local/lib/python2.7/dist-packages/django/forms/models.py" in choice
      904.         return (self.field.prepare_value(obj), self.field.label_from_instance(obj))
    File "/usr/local/lib/python2.7/dist-packages/django/forms/models.py" in label_from_instance
      955.         return smart_unicode(obj)
    File "/usr/local/lib/python2.7/dist-packages/django/utils/encoding.py" in smart_unicode
      39.     return force_unicode(s, encoding, strings_only, errors)
    File "/usr/local/lib/python2.7/dist-packages/django/utils/encoding.py" in force_unicode
      66.                 s = unicode(s)

    Exception Type: TemplateSyntaxError at /admin/ps/ps/add/
    Exception Value: Caught TypeError while rendering: coercing to Unicode: need string or buffer, NoneType found

【问题讨论】：

为什么缺少from/import 和重复from/import 所有相同的模块？

我看到% for field in line %，line 是什么？

@rednaw 它在模板中 /usr/local/lib/python2.7/dist-packages/django/contrib/admin/templates/admin/includes/fieldset.html 所以我也不知道跨度>

@KevinDTimm 那在哪里？我不明白你的意思对不起

你为什么还要return unicode(self.nom_du_site)？为什么不只是return self.nom_du_site？那一栏到底有什么？也许与此有关。

【参考方案1】：

首先，检查您通过 unicode 返回的内容是否为字符串。

如果不是字符串，可以改成这样的字符串（self.id是整数）

def __unicode__(self):
    return '%s' % self.id

接下来，如果仍然无法正常工作，请重新启动您的 ./manage.py shell 以使更改生效，然后重试。它应该可以工作。

最好的问候

【讨论】：

没有。无论您通过 __unicode__ 返回什么，都必须是 unicode 对象，而不是字节串。使用unicode(self.id)，或者，如果必须，使用u'%s' % self.id。 （确实，在这种情况下答案会起作用，因为 id 总是一个整数，但答案应该给出正确的实现，而不是偶然发生的事情。）

【参考方案2】：

当您有一个返回未输入字段的__unicode__ 方法时会发生此错误。任何空白字段都是None，Python 无法转换None，所以会出现错误。

在您的情况下，问题很可能出在 PCE 模型的 __unicode__ 方法上，特别是其返回的字段。

您可以通过返回默认值来防止这种情况：

def __unicode__(self):
   return self.some_field or u'None'

【讨论】：

顺便说一下（对于那些可能从深夜睡眼惺忪的人），它也可能是由__unicode__ 中的未返回任何内容 引起的。 :)

即使您的对象字段在更改页面上看起来不错，当相关字段之一 __unicode__ 返回无时，您也可以拥有它！

或者在 python3 (Django 2.0) - def __str__(self): return unicode(self.some_field) or "" - 我有一些字段为 null 并且数据已经在填充数据中 - 所以我可以不要从管理员中删除它们-返回默认值就可以了...

【参考方案3】：

当您在 __unicode__ 方法中返回对象而不是字符串时，可能会发生此错误。例如：

class Author(models.Model):
    . . . 
    name = models.CharField(...)


class Book(models.Model):
    . . .
    author = models.ForeignKey(Author, ...)
    . . .
    def __unicode__(self):
        return self.author  # <<<<<<<< this causes problems

为避免此错误，您可以将作者实例转换为 unicode：

class Book(models.Model):
    . . . 
    def __unicode__(self):
        return unicode(self.author)  # <<<<<<<< this is OK

【参考方案4】：

在我的情况下，这是另外一回事：我要保存的对象首先应该有一个 id（例如，应该调用 save()），然后才能设置任何类型的关系。

【参考方案5】：

返回值 def __unicode __ 应该与相关模型（表）的返回值相似，以便在 django 管理面板中正确查看“some_field”。 您还可以使用：

def __str__(self):
    return self.some_field

【参考方案6】：

用提供的函数替换之前的函数。最简单的解决方案是：

def __unicode__(self):

    return unicode(self.nom_du_site)