Question

I am new to python and django and i have a question regarding the redirect function.

This is a reduced version of my views.py file.

def page_index(request, error_message=''):
    print error_message

def add_page(request):
    return redirect('page_index') # this work fine
    return redirect('page_index', error_message='test') # this does not work

And here is a short version of my urls.py

urlpatterns = patterns(
    'x.views',
    url(r'^$', 'page_index', {'error_message': 't'}, name='page_index'),
    url(r'^add/$', 'add_page', name='add_page'),
)

When i try redirecting to page_index without the keyword argument everything works fine, but when i use the kwag i get the following error message:

NoReverseMatch at /pages/add/

Reverse for ‘page_index’ with arguments ‘()’ and keyword arguments ‘{‘error_message’: ‘test’}’ not found.

What am i doing wrong?

Answer 1

Short answer: There is no place in your url scheme for the ‘error_message’ keyword.

Longer answer:

The redirect() function is calling reverse() to build a URL; it is going to send the user’s browser to that URL by returning an HTTP response with a 302 redirect status code, and the new url. Any keyword arguments that you supply to reverse() are supposed to end up as part of the url — that’s how they get communicated to the user.

In your case, though, the url for ‘page_index` is just defined as ‘^$’ — this is the root url, which looks like ‘http://yoursite.com/’ in the browser.

If you want to be able to issue a redirect that contains other information, you will need to define a place for it in the url, or add it in a different way.

TwoThree ways are fairly common for this:

1. Use a query parameter — this sends the message to the client explicitly; if you aren’t careful, people can craft urls to make your index page say whatever they want it to.

   return redirect(reverse('page-index')+"?error_message=test"))
   

2. Stash the message in the session and pull it out when the next page loads — this requires that you have sessions configured, and keeps track of everything on the server side, rather than relying on the client to send you back the error message:

   def add_page(request):
       request.session['error_message'] = 'test'
       return redirect('page-index')
   
   def page_index(request):
       print request.session.get('error_message','')
   

3. Use the messages framework for this — this is preferred over ad-hoc session attributes, as long as you don’t need too many ‘types’ of message on the same page. If all you have is a space in your template for error message, though, then this is really easy:

   from django.contrib.messages import error
   
   def add_page(request):
       error(request, 'test')
       return redirect('page-index')
   

   And then in your base template, have a block like this somewhere (probably more complex than this; styled, even):

   {% for message in messages %}
       <p>{{ message }}</p>
   {% endfor %}
   

In bothall cases, though, you can remove the arguments from your urls.py — the message itself is not going to be part of the path component of the URL.

 urlpatterns = patterns(
    'x.views',
     url(r'^$', 'page_index', name='page_index'),
     url(r'^add/$', 'add_page', name='add_page'),
 )