Question

Is there a way to have a default parameter passed to a action in the case where the regex didnt match anything using django?

 urlpatterns = patterns('',(r'^test/(?P<name>.*)?$','myview.displayName'))  #myview.py def displayName(request,name):       # write name to response or something 

I have tried setting the third parameter in the urlpatterns to a dictionary containing ‘ and giving the name parameter a default value on the method, none of which worked. the name parameter always seems to be None. I really dont want to code a check for None if i could set a default value.

Clarification: here is an example of what i was changing it to.

 def displayName(request,name='Steve'):       return HttpResponse(name) #i also tried  urlpatterns = patterns('',       (r'^test/(?P<name>.*)?$',         'myview.displayName',         dict(name='Test')       ) ) 

when i point my browser at the view it displays the text ‘None’

Any ideas?

Answer 1

The problem is that when the pattern is matched against ‘test/’ the groupdict captured by the regex contains the mapping ‘name’ => None:

>>> url.match('test/').groupdict() {'name': None} 

This means that when the view is invoked, using something I expect that is similar to below:

view(request, *groups, **groupdict) 

which is equivalent to:

view(request, name = None) 

for ‘test/’, meaning that name is assigned None rather than not assigned.

This leaves you with two options. You can:

1. Explicitly check for None in the view code which is kind of hackish.
2. Rewrite the url dispatch rule to make the name capture non-optional and introduce a second rule to capture when no name is provided.

For example:

urlpatterns = patterns('',     (r'^test/(?P<name>.+)$','myview.displayName'), # note the '+' instead of the '*'     (r'^test/$','myview.displayName'), ) 

When taking the second approach, you can simply call the method without the capture pattern, and let python handle the default parameter or you can call a different view which delegates.