为什么DjangoJSONEncoder不处理代理对象？

Question

所以这是来自DjangoJSONEncoder的代码，它处理标准json编码器之外所需的大多数事情：

class DjangoJSONEncoder(json.JSONEncoder):
    """
    JSONEncoder subclass that knows how to encode date/time and decimal types.
    """
    def default(self, o):
        # See "Date Time String Format" in the ECMA-262 specification.
        if isinstance(o, datetime.datetime):
            r = o.isoformat()
            if o.microsecond:
                r = r[:23] + r[26:]
            if r.endswith('+00:00'):
                r = r[:-6] + 'Z'
            return r
        elif isinstance(o, datetime.date):
            return o.isoformat()
        elif isinstance(o, datetime.time):
            if is_aware(o):
                raise ValueError("JSON can't represent timezone-aware times.")
            r = o.isoformat()
            if o.microsecond:
                r = r[:12]
            return r
        elif isinstance(o, decimal.Decimal):
            return str(o)
        else:
            return super(DjangoJSONEncoder, self).default(o)

但是当它尝试编码代理对象时，它会失败并显示django.utils.functional.__proxy__ object at 0x7f53c6325ed0> is not JSON serializable

通过将DjangoJSONEncoder更改为：

，这很容易解决

from django.utils.functional import Promise
class DjangoJSONEncoder(json.JSONEncoder):
    """
    JSONEncoder subclass that knows how to encode date/time and decimal types.
    """
    def default(self, o):
        # See "Date Time String Format" in the ECMA-262 specification.
        if isinstance(o, datetime.datetime):
            r = o.isoformat()
            if o.microsecond:
                r = r[:23] + r[26:]
            if r.endswith('+00:00'):
                r = r[:-6] + 'Z'
            return r
        elif isinstance(o, datetime.date):
            return o.isoformat()
        elif isinstance(o, datetime.time):
            if is_aware(o):
                raise ValueError("JSON can't represent timezone-aware times.")
            r = o.isoformat()
            if o.microsecond:
                r = r[:12]
            return r
        elif isinstance(o, decimal.Decimal):
            return str(o)
        elif isinstance(o, Promise):  # Added these lines here 
            return unicode(o)
        else:
            return super(DjangoJSONEncoder, self).default(o)

但是写Django的人非常聪明。如果这是真正的解决方案，他们可能已经做到了。为什么他们没有这样做，那对unicode的调用，结合JSON编码使得这对DjangoJSONEncoder的错误修复？

我甚至在Django文档中找到了reference to this problem，所以它不像它不知道，我只是不明白为什么它不是默认值。