重构为 JSON 数组时，JSON 中的 Python 不可散列类型列表

Question

我一般都知道 python 如何处理 JSON（我认为），但我遇到了一些我无法解释的事情。

我最初在 api 端点中使用此代码来为 react 应用程序中的下拉菜单提供选项：

data = {
    "urgency_choices": URGENCY_CLASSES,
    "severity_choices": SEVERITY_CLASSES,
    "issue_classes": ISSUE_CLASSES,
    "flats": [(x.id, x.flat.name) for x in  OperationsFlat.objects.all()]
    }

然后我决定将其重构为提供一个“字段”的 JSON 数组，每个字段都有自己的选择键，以及它是否为必填字段：

data = {
    [
        {"name": "Urgency", "choices": URGENCY_CLASSES, "required": True},
        {"name": "Severity", "choices": SEVERITY_CLASSES, "required": True},
        {"name": "Issue Class", "choices": ISSUE_CLASSES, "required": True},
        {"name": "Flat", "choices": [(x.id, x.flat.name) for x in  OperationsFlat.objects.all()], "required": True}
    ]
}

错误是：

"name": "Flat", "choices": [(x.id, x.flat.name) for x in  OperationsFlat.objects.all()], "required": True}
TypeError: unhashable type: 'list'

在我看来，虽然列表的嵌套层次发生了变化，但python仍然需要以同样的方式对列表进行hash，那么为什么它在第一种形式中起作用，而在第二种形式中不起作用？

更多信息：

这是一个django rest框架APIView，APIView的返回返回一个Response对象，里面有这个对象。

完整的 TB，虽然我不确定它有多大用处：

Traceback (most recent call last):
  File "/Users/alexanderhalford/.pyenv/versions/xenia/lib/python3.5/site-packages/django/core/handlers/exception.py", line 34, in inner
    response = get_response(request)
  File "/Users/alexanderhalford/.pyenv/versions/xenia/lib/python3.5/site-packages/django/core/handlers/base.py", line 126, in _get_response
    response = self.process_exception_by_middleware(e, request)
  File "/Users/alexanderhalford/.pyenv/versions/xenia/lib/python3.5/site-packages/django/core/handlers/base.py", line 124, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/Users/alexanderhalford/.pyenv/versions/xenia/lib/python3.5/site-packages/django/views/decorators/csrf.py", line 54, in wrapped_view
    return view_func(*args, **kwargs)
  File "/Users/alexanderhalford/.pyenv/versions/xenia/lib/python3.5/site-packages/django/views/generic/base.py", line 68, in view
    return self.dispatch(request, *args, **kwargs)
  File "/Users/alexanderhalford/.pyenv/versions/xenia/lib/python3.5/site-packages/rest_framework/views.py", line 495, in dispatch
    response = self.handle_exception(exc)
  File "/Users/alexanderhalford/.pyenv/versions/xenia/lib/python3.5/site-packages/rest_framework/views.py", line 455, in handle_exception
    self.raise_uncaught_exception(exc)
  File "/Users/alexanderhalford/.pyenv/versions/xenia/lib/python3.5/site-packages/rest_framework/views.py", line 492, in dispatch
    response = handler(request, *args, **kwargs)
  File "/Users/alexanderhalford/work/nhuk/xenia/apps/operations/views.py", line 49, in get
    {"name": "Flat", "choices": {[(x.id, x.flat.name) for x in  OperationsFlat.objects.all()]}, "required": True}
TypeError: unhashable type: 'list'

Answer 1

问题是你有一组大括号 - { ... }，然后你有方括号 - [ ... ]。这意味着 Python 将您的结构解释为单个 set，您尝试向其中添加单个项目，即列表 - 但列表不能被散列，因为它们是可变的。

我不知道你真正想要什么格式，但也许你打算完全去掉大括号？那么你确实会有一个有效的字典列表。

data = [
    {"name": "Urgency", "choices": URGENCY_CLASSES, "required": True},
    {"name": "Severity", "choices": SEVERITY_CLASSES, "required": True},
    {"name": "Issue Class", "choices": ISSUE_CLASSES, "required": True},
    {"name": "Flat", "choices": [(x.id, x.flat.name) for x in  OperationsFlat.objects.all()], "required": True}
]

（或者，也许，您打算将其保留为包含单个项目的 dict，该项目是一个 dicts 列表 - 但是您需要一个密钥：data = {"data": [ ... ]}。）