NoReverseMatch at /blog/

Question

I am following "django by example" and i met the problem but i don't know what causes it.

The following is the error page:

---

NoReverseMatch at /blog/ Reverse for 'post_detail' with arguments '('', '', '')' not found. 1 pattern(s) tried: ['blog/(?P\d{4})/(?P\d{2})/(?P\d{2})/(?P[-\w]+)/$']

Request Method: GET

Request URL: http://127.0.0.1:8000/blog/

Django Version: 1.11

Exception Type: NoReverseMatch

Exception Value: Reverse for 'post_detail' with arguments '('', '', '')' not found. 1 pattern(s) tried: ['blog/(?P\d{4})/(?P\d{2})/(?P\d{2})/(?P[-\w]+)/$']

Exception Location: E:\workspace\pycharm\djangobyexample\mysite\env\lib\site-packages\django\urls\resolvers.py in _reverse_with_prefix, line 497

Python Executable: E:\workspace\pycharm\djangobyexample\mysite\env\Scripts\python.exe

Python Version: 3.5.2

Python Path: ['E:\workspace\pycharm\djangobyexample\mysite', 'E:\workspace\pycharm\djangobyexample\mysite\env\Scripts\python35.zip', 'E:\workspace\pycharm\djangobyexample\mysite\env\DLLs', 'E:\workspace\pycharm\djangobyexample\mysite\env\lib', 'E:\workspace\pycharm\djangobyexample\mysite\env\Scripts', 'c:\users\richard\appdata\local\programs\python\python35\Lib', 'c:\users\richard\appdata\local\programs\python\python35\DLLs', 'E:\workspace\pycharm\djangobyexample\mysite\env', 'E:\workspace\pycharm\djangobyexample\mysite\env\lib\site-packages']

---

---

Main URLConfiguration

urlpatterns = [
    url(r'^admin/', admin.site.urls),
    url(r'^blog/', include('blog.urls', namespace='blog', app_name='blog')),
]

---

blog/url.py

from django.conf.urls import url
from . import views

urlpatterns = [
    # post views
    # url(r'^$', views.post_list, name='post_list'),
    url(r'^$', views.PostListView.as_view(), name='post_list'),
    url(r'^(?P<year>\d{4})/(?P<month>\d{2})/(?P<day>\d{2})/(?P<post>[-\w]+)/$',
        views.post_detail,
        name='post_detail'),
    #url(r'^(?P<post_id>\d+)/share/$', views.post_share, name='post_share'),
]

views.py

from django.shortcuts import render, get_object_or_404
from .models import Post
from django.core.paginator import Paginator, EmptyPage, PageNotAnInteger
from django.views.generic import ListView
from .forms import EmailPostForm
from django.core.mail import send_mail


# Create your views here.

class PostListView(ListView):
    queryset = Post.published.all()
    context_object_name = 'posts'
    paginate_by = 3
    template_name = 'blog/post/list.html'



def post_detail(request, year, month, day, post):
    post = get_object_or_404(Post, slug=post,
                             status='published',
                             publish__year=year,
                             publish__month=month,
                             publish__day=day)
    return render(request, 'blog/post/detail.html', {'post': post})

models.py

from django.db import models
from django.utils import timezone
from django.contrib.auth.models import User
from django.core.urlresolvers import reverse


class PublishedManager(models.Manager):
    def get_query(self):
        return super(PublishedManager, self).get_query().filter(status='published')


class Post(models.Model):
    STATUS_CHOICES = {
        ('draft', 'Draft'),
        ('published', 'Published'),
    }
    title = models.CharField(max_length=250, primary_key=True)
    slug = models.SlugField(max_length=250, unique_for_date='publish')
    author = models.ForeignKey(User, related_name='blog_post')
    body = models.TextField()
    publish = models.DateTimeField(default=timezone.now)
    created = models.DateTimeField(auto_now_add=True)
    updated = models.DateTimeField(auto_now=True)
    status = models.CharField(max_length=10, choices=STATUS_CHOICES, default='draft')

    class Meta:
        # Telling django to sort results by the publish field in descending order by default when we query the database
        ordering = ('-publish',)

    def __str__(self):
        return self.title

    objects = models.Manager()
    published = PublishedManager()

    def get_absolute_url(self):
        return reverse('blog:post_detail', args=[self.publish.year,
                                                 self.publish.strftime('%m'),
                                                 self.publish.strftime('%d'),
                                                 self.slug])

detail.html

{% extends "blog/base.html" %}

{% block title %}{{ post.title }}{% endblock %}

{% block content %}
    <h1>{{ post.title }}</h1>
    <p class="date">
        Published {{ post.publish }} by {{ post.author }}
    </p>
    {{ post.body|linebreaks }}

{% endblock %}

list.html

{% extends "blog/base.html" %}

{% block title %}My Blog{% endblock %}

{% block content %}
    <h1>My Blog</h1>
    {% for post in posts %}
        <h2>

            <a href="{{ post.get_absolute_url }}">
                {{ post.title }}
            </a>
        </h2>
        <p class="date">
            Published {{ post.publish }} by {{ post.author }}
        </p>
        {{ post.body|truncatewords:30|linebreaks }}
    {% endfor %}
    {% include "pagination.html " with page=page_obj %}
{% endblock %}

base.html

{% load staticfiles %}

<html>
<head>
    <meta charset="UTF-8">
    <title>{% block title %}{% endblock %}</title>

</head>
<body>
    <div id="content">
        {% block content %}
        {% endblock %}
        </div>
        <div id="sidebar">
            <h2>My blog</h2>
            <p>This is my blog.</p>
        </div>
</body>
</html>

Answer 1

This line is giving you the error, because the arguments are invalid.

<!-- <a href="{% url 'blog:post_detail' post.year post.month post.day %}">-->

The post does not have year, month and day attributes -- they are attributes of post.publish.

You are already using {{ post.get_absolute_url }} on the next line of the template to get the url. Since the url tag line is inside an html comment <!-- -->, the easiest fix is to simply delete the line.