How to redirect in webapp2

Question

Hello I am learning webapp2 , my doubt is there are three pages 1: /blog for viewing all the blogs posted which are linked to their permalink 2: /blog/newpost for getting the newpost for blog , it contains only title and blog as input while user clicks on submit button it redirects to some permalink(this works!!!) 3: and last is /blog/(somepermalink) where user is redirected to this page in step 2

My probelm is first page gives all the list of blogs created and when user clicks on some blog i want to redirect to step 3 but unfortunately it gives me 404 error Here are my codes

class Handler(webapp2.RequestHandler):
  def write(self, *a, **kw):
    self.response.out.write(*a, **kw)

  def render_str(self, template, **params):  
    t = jinja_env.get_template(template)
    return t.render(params)

  def render(self, template, **kw):
    self.write(self.render_str(template, **kw))  

 class Blog(db.Model):
   title = db.StringProperty(required = True)
   blog = db.TextProperty(required = True)
   created = db.DateTimeProperty(auto_now_add = True) 


 class MainPage(Handler):
   def render_front(self, title="", blog="", error=""):
     self.render("newpost.html", title=title, blog=blog, error=error)

   def get(self):
     self.render_front()

   def post(self):
     title = self.request.get("title")
     blog = self.request.get("blog")

     if title and blog:
       a = Blog(title=title, blog=blog)
       a_key = a.put()
     #sleep is used because of replication lag time
       sleep(0.1)   
     #redirect to some permalink
       self.redirect("/blog/%d" % a_key.id())
    else:
      error = "both title and post are needed"
      self.render_front(title, blog, error)  


class BlogPostHandler(Handler):
   def render_blog(self, title="", blogs=""):
     blogs = db.GqlQuery("SELECT * FROM Blog ORDER BY created DESC")
     self.render("blogpage.html", title=title, blogs=blogs)

  def get(self):
    self.render_blog()

class PermaLink(MainPage):
  def get(self, blog_id):
    s = Blog.get_by_id(int(blog_id))
    self.render("blogpage.html", blogs = [s])


app = webapp2.WSGIApplication([('/blog',BlogPostHandler),
                           ('/blog/newpost',MainPage),
                           ('/blog/(\d+)', PermaLink)], 

Answer 1

There is nothing obvious in the code you provided to indicate that there's a bug. Since the redirect in your MainPage request handler does properly redirect and load a blog post, I suspect that the problem is in how you are creating links within the jinja2 template used by BlogPostHandler. Here are a few things to look out for:

• The links are using /blog/ instead of /blogs/ (plural).
• Accidental whitespace in your link: /blog/ 1234.
• You're using absolute links instead of relative links.
  • Absolute: href="/blog/{{ post.id }}" (leading /)
  • Relative: href="blog/{{ post.id }}" (no leading /, which would link to /blog/blog/<id>)
• The blog post ID is being rendered as an integer and not a long, which can happen when using Google App Engine's Datastore.
  • Integer: /blog/1234
  • Long: /blog/1234L

Answer 2

Maybe worth mentioning, adding to the first reply: one may enjoy more flexibility when opting for the extended routes:

app = webapp2.WSGIApplication([
    webapp2.Route(r'/blog', handler=BlogPostHandler, name='BlogPost'),
    webapp2.Route(r'/blog/newpost', handler=MainPage, name='MainPage'),
    webapp2.Route(r'/blog/<:\d+>', handler=PermaLink, name='PermanentLink'),
])

The last line above indicates a route to /blog/, the same way as your initial code. If you want to indicate any possible path after /blog/, you should use Route r'/blog/<:.*>', instead.