问表单验证不起作用Django和打印只在消息上

EN

efrom django import forms
from django.contrib.auth.models import User
from django.core.exceptions import ValidationError
from django.forms.widgets import CheckboxSelectMultiple
from blog.models import Category
from wsgiref.validate import validator


class PostForm(forms.Form):
    title = forms.CharField(max_length = 100, min_length= 1,)
    slug = forms.SlugField(allow_unicode=True)
    message = forms.CharField(widget = forms.Textarea)
    banner = forms.ImageField()
    category = forms.ModelChoiceField(queryset=Category.objects)
    authors = forms.ModelChoiceField(queryset=User.objects, 
    widget=CheckboxSelectMultiple)    
    def clean(self):
        cleaned_data = super(PostForm, self).clean()
        slug = cleaned_data['slug']

    if not "sepehr" in slug:
        raise forms.ValidationError("here we have some errors !")
    return cleaned_data

class HoemView(generic.TemplateView):
    template_name = 'blog2/create.html'
    def get(self, request):
        form = PostForm()
        context = {
            'form':form
         }
        return render(request, self.template_name, context)

    def post(self, request):
         form = PostForm(request.POST, request.FILES)

        if form.is_valid():
             return HttpResponse('form is valid!')

        return HttpResponse('form is not valid!')