Django错误 __str__返回非字符串（类型__proxy__）

Question

我有一些使用 GenericForeignKey 的模型，当我尝试使用 Django 后台工具访问它们时，我可以看到记录列表，但是当我点击其中的一个记录时，会出现以下错误：__str__ returned non-string (type __proxy__)。

以下是其中一个模型的代码：

class ReservationComponent(models.Model):
    reservation = models.ForeignKey(Reservation, on_delete=models.PROTECT, related_name='components', verbose_name=_(''))
    day = models.DateField(verbose_name=_('Day'))
    content_type = models.ForeignKey(ContentType, on_delete=models.PROTECT)
    object_id = models.PositiveIntegerField()
    content_object = GenericForeignKey('content_type', 'object_id')

    class Meta:
        verbose_name = _("Reservation Component")
        verbose_name_plural = _("Reservations Components")

    def __str__(self):
        return "[{}][{}]{} - [{}]{}".format(self.id, self.reservation, self.day, self.content_type, self.object_id)

这是整个跟踪信息：

Internal Server Error: /es/admin/ReservationsManagerApp/reservationcomponent/14/change/
Traceback (most recent call last):
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/core/handlers/exception.py", line 35, in inner
    response = get_response(request)
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/core/handlers/base.py", line 158, in _get_response
    response = self.process_exception_by_middleware(e, request)
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/core/handlers/base.py", line 156, in _get_response
    response = response.render()
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/template/response.py", line 106, in render
    self.content = self.rendered_content
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/template/response.py", line 83, in rendered_content
    content = template.render(context, self._request)
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/template/backends/django.py", line 61, in render
    return self.template.render(context)
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/template/base.py", line 175, in render
    return self._render(context)
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/template/base.py", line 167, in _render
    return self.nodelist.render(context)
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/template/base.py", line 943, in render
    bit = node.render_annotated(context)
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/template/base.py", line 910, in render_annotated
    return self.render(context)
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/template/loader_tags.py", line 155, in render
    return compiled_parent._render(context)
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/template/base.py", line 167, in _render
    return self.nodelist.render(context)
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/template/base.py", line 943, in render
    bit = node.render_annotated(context)
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/template/base.py", line 910, in render_annotated
    return self.render(context)
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/template/loader_tags.py", line 155, in render
    return compiled_parent._render(context)
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/template/base.py", line 167, in _render
    return self.nodelist.render(context)
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/template/base.py", line 943, in render
    bit = node.render_annotated(context)
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/template/base.py", line 910, in render_annotated
    return self.render(context)
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/template/loader_tags.py", line 67, in render
    result = block.nodelist.render(context)
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/template/base.py", line 943, in render
    bit = node.render_annotated(context)
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/template/base.py", line 910, in render_annotated
    return self.render(context)
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/template/loader_tags.py", line 67, in render
    result = block.nodelist.render(context)
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/template/base.py", line 943, in render
    bit = node.render_annotated(context)
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/template/base.py", line 910, in render_annotated
    return self.render(context)
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/template/defaulttags.py", line 211, in render
    nodelist.append(node.render_annotated(context))
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/template/base.py", line 910, in render_annotated
    return self.render(context)
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/template/loader_tags.py", line 194, in render
    return template.render(context)
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/template/base.py", line 177, in render
    return self._render(context)
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/template/base.py", line 167, in _render
    return self.nodelist.render(context)
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/template/base.py", line 943, in render
    bit = node.render_annotated(context)
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/template/base.py", line 910, in render_annotated
    return self.render(context)
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/template/defaulttags.py", line 211, in render
    nodelist.append(node.render_annotated(context))
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/template/base.py", line 910, in render_annotated
    return self.render(context)
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/template/defaulttags.py", line 211, in render
    nodelist.append(node.render_annotated(context))
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/template/base.py", line 910, in render_annotated
    return self.render(context)
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/template/defaulttags.py", line 314, in render
    return nodelist.render(context)
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/template/base.py", line 943, in render
    bit = node.render_annotated(context)
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/template/base.py", line 910, in render_annotated
    return self.render(context)
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/template/base.py", line 993, in render
    output = self.filter_expression.resolve(context)
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/template/base.py", line 676, in resolve
    obj = self.var.resolve(context)
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/template/base.py", line 802, in resolve
    value = self._resolve_lookup(context)
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/template/base.py", line 864, in _resolve_lookup
    current = current()
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/contrib/admin/helpers.py", line 137, in label_tag
    contents = conditional_escape(self.field.label)
  File "/Users/hugovillalobos/Documents/Code/IntellibookProject/IntellibookVenv/lib/python3.6/site-packages/django/utils/html.py", line 78, in conditional_escape
    text = str(text)
TypeError: __str__ returned non-string (type __proxy__)
[22/Aug/2018 02:52:14] "GET /es/admin/ReservationsManagerApp/reservationcomponent/14/change/ HTTP/1.1" 500 489781

- HuLu ViCa

---

你能分享整个回溯吗？ - Olivier Melançon

你如何导入 ugettext？ - Selcuk

from django.utils.translation import ugettext_lazy as _ - HuLu ViCa

你可以尝试使用import ugettext而不是import ugettext_lazy吗？ - Selcuk

@Selcuk 我已经尝试过了，但不是那个问题。我在所有的模型中都使用了它，问题只出现在使用GenericForeignKey的模型中。 - HuLu ViCa

这可能是Django管理界面中的一个错误。您尝试过删除“verbose_name”以查看是否有所帮助吗？ - Selcuk

Answer 1

我尝试重现了这个问题，并且成功了。问题出在 ugettext_lazy 上。

你应该使用 ugettext 而不是 ugettext_lazy。因此，你的导入应该是：

from django.utils.translation import <b>ugettext</b> as <b>_</b>

测试环境为Django==1.11。

- JPG

---

它有效了！在我的情况下，我有一个“Enum”，其值为“gettext_lazy”。这些值的字符串表示显示为只读值。将“gettext_lazy”替换为“gettext”解决了这个问题。 - Eerik Sven Puudist

Answer 2

在模型声明中应该使用gettext_lazy。这对于verbose_name翻译非常有帮助（何时应该使用ugettext_lazy？）。因此，为了绕过在__str__方法中的问题，您可以简单地使用str()内置函数来强制返回字符串而不是__proxy__。 如果您需要使用字符串格式（例如：'我的对象是：{}'.format(object)），则必须使用format_lazy并使用str()函数强制转换为字符串。

例如：

from django.db import models
from django.utils.text import format_lazy
from django.utils.translation import gettext_lazy as _

class MyThing(models.Model):
    name = models.CharField(help_text=_(
        'help text for MyThing model', 'This is the help text'))

    class Meta:
        verbose_name = _("My thing")

    def __str__(self):
        if self.name:
            # Force str to avoid __proxy__
            return str(format_lazy('{txt} {name}', txt=_('My name is'), name=self.name))
        # Force str to avoid __proxy__
        return str(_("No name"))

- Martin

Answer 3

我曾经遇到过类似的错误，原因是在 _("") 部分没有填写任何内容，在管理员创建对象时出现了这个错误。你在预订字段中也犯了同样的错误，没有填写 verbose_name 的值。

- Mohammadreza Taheri

---

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