Форма не проходит валидацию. Django 2.1.2

from django.shortcuts import render, render_to_response
    from django.http import HttpResponse
    from django.views.generic import View
    from django.contrib import messages
    from guess.models import Post, Comments
    from guess.forms import PostForm, CommentsForm
    # Create your views here.
    class GuessBook(View):
        def get(self, request):
            get_date=Post.objects.all()
            context = {'post':get_date}
            return render_to_response('guessApp/form.html', context)
def post(self,request):
            print(request.POST)
            form = PostForm(request.POST)
            if form.is_valid():
                db = form.save()
            else:
                print('error')
            c = {'form':form}
            return render(request,'guessApp/form.html', c )

from django.db import models
from django.utils import timezone
# Create your models here.
class Post(models.Model):
    article = models.CharField(max_length=25)
    text=models.TextField(max_length=200)
    is_created=models.DateTimeField('Date published')
 
    def __str__(self):
        return self.article

from django import forms
from django.core.exceptions import ValidationError
from guess.models import Post
class PostForm(forms.ModelForm):
    class Meta:
        model = Post
        fields=[
            'article',
            'text'
        ]