Работающий код модели

# -*- coding: utf-8 -*-
from __future__ import unicode_literals
from django.db import models
from django.contrib import admin
from django.utils import timezone
from rte import RTEField
from django.urls import reverse

class Razdel(models.Model):
    name = models.CharField(max_length=50, unique = True)

    def __unicode__(self):
        return self.name 
        
class Article(models.Model):
    title = models.CharField(max_length=150,verbose_name = 'Название статьи')
    body = RTEField(default = '')
    timestamp = models.DateTimeField(default = timezone.now, db_index = True, verbose_name = "Опубликована")
    razdel = models.ForeignKey(Razdel,on_delete=models.SET_NULL,blank=True,null=True,verbose_name = 'Раздел')
    
    def get_absolute_url(self):
        return reverse('article', args=[str(self.id)])
  
    def get_list_url(self):
        return reverse('articles', args=[str(self.razdel.id)])    


class ArticleAdmin(admin.ModelAdmin):
    list_display = ('title','timestamp','razdel')

admin.site.register(Article,ArticleAdmin)

class RazdelAdmin(admin.ModelAdmin):
    list_display = ['name']

admin.site.register(Razdel,RazdelAdmin)