.items在Django模板中的defaultdict上不起作用

问题描述：

我无法让.items在我的Django模板中工作:

I can't get .items to work in my Django template:

从CBV的get_context_data复制并粘贴:

copy and paste from my CBV's get_context_data:

    context['data'] = assertion_dict
    context['dataitems'] = assertion_dict.items()

    return context

从我的模板复制并粘贴:

copy and paste from my template:

  <h3>data dump</h3>
  {{data}}

  <h3>dataitems</h3>
  {% for key, value in dataitems %}
     {{ key }}: {{ value }} <br/>
  {% endfor %}

  <h3>data.items</h3>
  {% for key, value in data.items %}
     {{ key }}: {{ value }} <br/>
  {% endfor %}

  <h3>Not found test</h3>
  {{ i_dont_exist }}

输出:

**data dump**
defaultdict(<class 'list'>, {<BadgeType: Talent>: [<BadgeAssertion: Blender Blue Belt>], <BadgeType: Achievement>: [<BadgeAssertion: MyBadge#1>, <BadgeAssertion: MyBadge#1>, <BadgeAssertion: MyBadge#2>], <BadgeType: Award>: [<BadgeAssertion: Copy of Copy of Blenbade>]})

**dataitems**
Talent: [<BadgeAssertion: Blender Blue Belt>]
Achievement: [<BadgeAssertion: MyBadge#1>, <BadgeAssertion: MyBadge#1>, <BadgeAssertion: MyBadge#2>]
Award: [<BadgeAssertion: Copy of Copy of Blenbade>]

**data.items**

**Not found test**
DEBUG WARNING: undefined template variable [i_dont_exist] not found

为什么第二个版本不起作用，我在模板中使用data.items?

Why isn't the second version working, where I use data.items in my template?

答

这是 Django中的已知问题:您无法遍历模板中的defaultdict.文档建议处理此问题的最佳方法是:将您的defaultdict转换为dict，然后再传递给模板:

This is a known issue in Django: you cannot iterate over a defaultdict in a template. The docs suggest that the best way to handle this is to convert your defaultdict to a dict before passing it to the template:

context['data'] = dict(assertion_dict)

顺便说一句，它不起作用的原因是，当您在模板中调用{{ data.items }}时，Django将首先尝试找到data['items']，然后是data.items. defaultdict将为前者返回默认值，因此Django将不会尝试后者，而您最终将尝试遍历默认值而不是dict.

The reason it doesn't work, by the way, is that when you call {{ data.items }} in your template, Django will first attempt to find data['items'], and then data.items. The defaultdict will return a default value for the former, so Django will not attempt the latter, and you end up trying to loop over the default value instead of the dict.

.items在Django模板中的defaultdict上不起作用

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