Django JSONField, that don't suck!

fields.py

"""
Works with SOUTH, and output on the same widget an HTML list with the value of the field

   class MyModel(models.Model):
        data = JSONField()

You will need simplejson installed with pip, Django 1.3+
"""

from django.db.models.fields import Field
from django.core.serializers.json import DjangoJSONEncoder
from django.forms.widgets import Textarea
from django.core import exceptions
from django.utils import simplejson as json
from django.utils.safestring import mark_safe

from simplejson.decoder import JSONDecodeError

def dict_to_html(obj, padding=0):
    lines = list()
    lines.append('<ul style="margin: 0; padding-left: %s0px" >' % padding)
    if type(obj) is list:
        obj = dict([e for e in enumerate(obj)])
    if type(obj) is unicode:
        return '%s' % obj
    for key, value in obj.iteritems():
        if isinstance(value, dict):
            lines.append('<li>%s: ' % key)
            lines.append('%s' % dict_to_html(value, padding+1))
            lines.append('</li>')
        else:
            lines.append('<li>%s: %s</li>' % (key, value))
    lines.append('</ul>')
    return '\n'.join(lines)

class RenderJSONWidget(Textarea):
    def render(self, name, value, attrs=None):
        if value is None or value == '':
            json_render = ''
        else:
            try:
                json_render = dict_to_html(json.loads(value))
            except JSONDecodeError:
                json_render = 'This value is not a valid JSON string.'

        json_render = '<div style="display:block; margin-left: 10em;">\n%s' % json_render

        textarea_field = super(RenderJSONWidget, self).render(name, value, attrs)
        textarea_field += '</div>'
        return mark_safe("%s <br/> %s " % (json_render, textarea_field))

class SortedJSONEncoder(DjangoJSONEncoder):
    def __init__(self, **kwargs):
        kwargs['sort_keys'] = True
        super(SortedJSONEncoder, self).__init__(**kwargs)

class JSONField(Field):
    description = "JSON encoded string"
    default_error_messages = {
        'invalid': '%s is not a valid JSON string.',
    }

    def __init__(self, verbose_name=None, name=None, **kwargs):
        Field.__init__(self, verbose_name, name, **kwargs)

    def to_python(self, value):
        if value is None:
            return None
        if isinstance(value, dict):
            return value
        if isinstance(value, list):
            return value

        try:
            return json.loads(value)
        except JSONDecodeError:
            raise exceptions.ValidationError(self.error_messages['invalid'] % str(value))

    def get_prep_value(self, value):
        return self.to_python(value)

    def get_db_prep_value(self, value, connection, prepared=False):
        if not prepared:
            value = json.dumps(value, cls=SortedJSONEncoder)
        return value

    def formfield(self, **kwargs):
        kwargs.update({'widget': RenderJSONWidget})
        return super(JSONField, self).formfield(**kwargs)

    def value_to_string(self, obj):
        val = self._get_val_from_obj(obj)
        return '' if val is None else json.dumps(val)

    def south_field_triple(self):
        from south.modelsinspector import introspector
        args, kwargs = introspector(self)
        return 'django.db.models.TextField', args, kwargs