Hello, everyone!
This issue occurs using Django 4.2.19: when I run the server and navigate to the “about” or “contact” pages, I get a 404 error raised by blog.views.PostDetailView. It appears that the URL pattern for slug:slug/ is capturing routes like /contact/ and /about/ because of its placement in urls.py.

Here’s my code:

PYTHONCopied
# views.py
from django.views import generic
from django.conf import settings
from django.core.mail import send_mail
from django.shortcuts import reverse

from .models import Post
from .forms import ContactForm

class PostListView(generic.ListView):
    model = Post
    queryset = Post.objects.all()
    context_object_name = 'posts'
    template_name = 'post_list.html'
    paginate_by = 5

class PostDetailView(generic.DetailView):
    model = Post
    context_object_name = 'post'
    template_name = 'post_detail.html'

class SuccessView(generic.TemplateView):
    template_name = 'success.html'

class ContactView(generic.FormView):
    form_class = ContactForm
    template_name = 'contact.html'

    def get_success_url(self):
        return reverse('blog:contact')

    def form_valid(self, form):
        email = form.cleaned_data.get('email')
        subject = form.cleaned_data.get('subject')
        message = form.cleaned_data.get('message')

        full_message = f"""
            Received message below from {email}, {subject}
            ______________________
            {message}
        """
        send_mail(
            subject='Received contact form from submission',
            message=full_message,
            from_email=settings.DEFAULT_FROM_EMAIL,
            recipient_list=[settings.NOTIFY_EMAIL],
        )
        return super(ContactView, self).form_valid(form)

class AboutView(generic.TemplateView):
    template_name = 'about.html'

PYTHONCopied
# urls.py
from django.urls import path 

from .views import PostListView, PostDetailView, ContactView, SuccessView, AboutView 

app_name = 'blog'

urlpatterns = [
    path('', PostListView.as_view(), name='post_list'),
    path('<slug:slug>/', PostDetailView.as_view(), name='post_detail'),
    path('contact/', ContactView.as_view(), name='contact'),
    path('success/', SuccessView.as_view(), name='success'),
    path('about/', AboutView.as_view(), name='about'),
] 

PYTHONCopied
# models.py
from django.db import models
from django.urls import reverse
from django.utils import timezone
from django.template.defaultfilters import slugify

from tinymce.models import HTMLField

class Post(models.Model):
    title = models.CharField(max_length=255)
    description = models.CharField(max_length=255)
    slug = models.SlugField(null=False, unique=True)
    body = HTMLField()
    pub_date = models.DateField(default=timezone.now)

    class Meta:
        ordering = ['-pub_date']
        verbose_name = 'Post'
        verbose_name_plural = 'Posts'

    def __str__(self):
        return self.title

    def get_absolute_url(self):
        return reverse('blog:post_detail', kwargs={'slug': self.slug})

    def save(self, *args, **kwargs):
        if not self.slug:
            self.slug = slugify(self.title)
        return super().save(*args, **kwargs)

BASHCopied
# python3 manage.py runserver
System check identified no issues (0 silenced).
February 21, 2025 - 13:22:35
Django version 4.2.19, using settings 'config.settings'
Starting development server at http://127.0.0.1:8000/
Quit the server with CONTROL-C.

Not Found: /contact/
[21/Feb/2025 13:22:47] "GET /contact/ HTTP/1.1" 404 2612
Not Found: /favicon.ico
[21/Feb/2025 13:22:47] "GET /favicon.ico HTTP/1.1" 404 3330

PLAINTEXTCopied
Page not found (404)

No Post found matching the query

Request Method:     GET
Request URL:    http://127.0.0.1:8000/contact/
Raised by:  blog.views.PostDetailView

Using the URLconf defined in config.urls, Django tried these URL patterns, in this order:
    admin/
    [name='post_list']
    <slug:slug>/ [name='post_detail']

The current path, contact/, matched the last one.

However, when I change urls.py to the following:

PYTHONCopied
# urls.py
from django.urls import path 

from .views import PostListView, PostDetailView, ContactView, SuccessView, AboutView 

app_name = 'blog'

urlpatterns = [
    path('', PostListView.as_view(), name='post_list'),
    path('contact/', ContactView.as_view(), name='contact'),
    path('success/', SuccessView.as_view(), name='success'),
    path('about/', AboutView.as_view(), name='about'),
    path('<slug:slug>/', PostDetailView.as_view(), name='post_detail'),
] 

This reordering fixes the issue. Why does the original ordering cause the wrong URL to be matched, and what is the best practice to prevent this type of conflict?