Django url pattern with 2 parameters misinterprets the second parameter

Question

I tried to use this pattern to pass 2 parameters in an URL, where the second parameter is optional. This is my code:

urlpatterns = patterns('',
    url(r'^topic/(?P<topic>.*)/(?P<page>.*)/$', activities_list, 
    url(r'^topic/(?P<topic>.*)/$', activities_list, name='activities'),name='activities_page'),
)

This works, except when the second parameter is 1. In that case, topic is topic/1 and and page is None. It works for any other number as a second parameter.

Who can put me in the right direction to solve this bug?

UPDATE, this is getting weird

After trying several things, I discovered that this template tag makes the problem:

<img src="{{recommendation.user_picture_url}}" />

When I delete this tag, or even remove it from the src attribute and place it outside the image tag, the URL works. The variable contains a URL to a LinkedIn avatar on Linkedin's servers.

This is my view

def activities_list(request, topic, page=1):

    print topic
    print page
    ...
    return render_to_response(...

I don't understand why my view is getting the wrong parameters from the URL (as seen in the prints), while the hole response hasn't even been rendered yet.

Update: Solved! (see below)

I would recommend 2 things - 1. Change the order of the 2 URL patterns, 2. Narrow the regex match to something like `[\w_-]+` if you can.. — karthikr, Oct 18 '13 at 14:08

falsetru · Answer 1 · 2013-10-19T05:13:52.550

1

Use non-greey qualifier (.*? or .+?):

urlpatterns = patterns('',
    url(r'^topic/(?P<topic>.+?)/$', activities_list, name='activities'),
    url(r'^topic/(?P<topic>.+?)/(?P<page>.+?)/$', activities_list, name='activities_page'),
)

For page number, \d+ is more appropriate.

urlpatterns = patterns('',
    url(r'^topic/(?P<topic>.*?)/$', activities_list, name='activities'),
    url(r'^topic/(?P<topic>.*?)/(?P<page>\d+)/$', activities_list, name='activities_page'),
)

Instead of (?P<topic>.*?), you can also use (?P<topic>[^/]+)

edited Oct 19 '13 at 05:13

answered Oct 18 '13 at 13:02

falsetru

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This doesn't seem to work. If I add the `?` in both parameters, _topic_ is `topic1/1/None`. This is only when the page parameter is 1, it does work with any other number. (I also tried copy pasting your entire code) – JacobF Oct 18 '13 at 14:04
@jvannistelrooy, What about `r'^topic/(?P[^/]+)/$'` and `r'^topic/(?P[^/]+)/(?P\d+)/$'` – falsetru Oct 19 '13 at 05:13
It sure was helpful, but it did not solve my problem. – JacobF Oct 20 '13 at 15:58

JacobF · Accepted Answer · 2013-10-18T16:27:06.157

After a lot of digging I found that when pictures in my test-database are missing, the template tag will give a None value in the image tag src attribute. This caused a request to the server to look for the image on URL /topic/1/None. Somehow, this happened even before the response was send to the client, so that my view received new, wrong, parameters.

This tag in my template on page .../topic/1/ requests the image from .../topic/1/None, sending wrong parameters.

<img src="{{recommendation.user_picture_url}}" />

PS Thanks falsetru for the improvements in the regex

Django url pattern with 2 parameters misinterprets the second parameter

2 Answers2