django reverse() url lookups

25 May 2008

There is a useful django template tag :

{% url app.views.viewfunc %}

which is the same as:

reverse('app.views.viewfunc')

that should lookup through your urls.py to find the url pattern that matches that view. it should then return the formatted URL. this allows you to configure all of your urls in your urls.py file(s) and keep your templates

this often does not work if your reg-ex is complicated eg.

r'^track/?(?P<slug>.+)$'

where there may or may not be a /
and there may or may not be a slug

There is simply no way that it can reverse that reg-ex and figure out what the URL should/could be.

since using {% url ... %} is very useful the best solution I think is to keep your reg-ex simpler and to use multiple confs for the multiple situations. and then NAME them and refer to the name rather than the view in {% url .. %} and reverse()

urlpatterns = pattern('',

    #  track/q=XYZ<br />        url(r'^ticker/$',<br />         view = 'desk.views.track',<br />            name = 'track_detail'<br />     ),

    # track/XYZ<br />       url(r'^track/(?P<slug>.+)$',<br />          view = 'desk.views.track',<br />            name = 'track_detail_by_url'<br />      ),<br />    )

<form action="{% url track_detail %}"><br />    <input type="text" name="q" /><br />    </form>

but I still can't get this to work:
link to the track

also, its django policy that templates should not raise exceptions. they fail silently and return "". I suppose that's because the "designers" freak every time they see an exception.

but in this case I find it very troublesome so in defaulttags.py I modified it, line 369:

except NoReverseMatch:<br />        assert False, "didn't match reverse view_name:%s" % (self.view_name)<br />      #return ''

to simply fail messily


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