Django REST - AssertionError: `fields` must be a list or tuple

Question

When querying Django via REST using the Django REST framework I get the error,

  File "/folder/pythonenv/project/lib/python2.7/site-packages/rest_framework/serializers.py", line 241, in get_fields
    assert isinstance(self.opts.fields, (list, tuple)), '`fields` must be a list or tuple'
AssertionError: `fields` must be a list or tuple

My settings are....

settings.py

THIRD_PARTY_APPS = (
        'south',  # Database migration helpers:
        'crispy_forms',  # Form layouts
        'rest_framework',
    )

REST_FRAMEWORK = {
                'DEFAULT_PERMISSION_CLASSES': (
                    'rest_framework.permissions.AllowAny',
                )
    }

views

from django.shortcuts import render
from rest_framework import viewsets
from quickstart.serializers import from quickstart.serializers import TicketInputSerializer
from models import Abc

class TicketInputViewSet(viewsets.ModelViewSet):
    queryset = Abc.objects.all()
    serializer_class = TicketInputSerializer

urls.py

router = routers.DefaultRouter()
router.register(r'ticket', views.TicketViewSet)

urlpatterns = patterns('',
    url(r'^', include(router.urls)),
    url(r'^test', include('rest_framework.urls', namespace='rest_framework')),

) 

Serializers

from models import Abc
from django.contrib.auth.models import User, Group
from rest_framework import serializers

class TicketInputSerializer(serializers.HyperlinkedModelSerializer):
    class Meta:
        model = Abc
        fields = ('test',)

Models

from django.db import models

class Abc(models.Model):
    test = models.CharField(max_length=12)

Any ideas ?

Answer 1

You need to use a tuple or list for fields, to represent a tuple with single item you need to use a trailing comma:

fields = ('test', )

Without a comma fields = ('test') is actually equivalent to fields = 'test'.

From docs:

A special problem is the construction of tuples containing 0 or 1 items: the syntax has some extra quirks to accommodate these. Empty tuples are constructed by an empty pair of parentheses; a tuple with one item is constructed by following a value with a comma (it is not sufficient to enclose a single value in parentheses). Ugly, but effective.

Answer 2

('test') is not a tuple, it is the same value as simply 'test'.

You should add a trailing comma to create a singleton tuple:

fields = ('test',)

Or you can use a list and don't bother about the commas:

fields = ['test']