Using variables in Django urlpatterns

The components of the URLs of the Django app I'm working on are very 'pluggable', and different combinations of them get used in vario开发者_StackOverflow社区us urlpatterns, so our urls.py looks something like:

rev = r'(/R\.(?P<rev>\d+))?'
repo_type= r'^(?P<repo_type>svn|hg)/'
path = r'/dir/(?P<path>.*)$'
# etc.

urlpatterns = patterns('',
    (repo_type_param + r'view-source' + opt_rev_param + path_param, view_source),
    (repo_type_param + r'history' + path_param, history),
    (repo_type_param + r'revision' + opt_rev_param + r'/$', revision),
) #etc.

Which seems like a nice way to keep things clean. However, I found I kept getting NoReverseMatch errors when I tried to reverse any of the views pointed to by the urlpatterns. After a lot of tinkering, I found that using the full raw string in the pattern, rather than concatenating the substrings, fixed the problem.

So, is it really necessary to use only raw strings in urlpatterns? I couldn't find this documented anywhere. Bug or feature? Having to copy and paste regex patterns that get used repeatedly seems like a violation of DRY.

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I'm not sure about concatenation, but I know you can format raw strings and use them in urlpatterns. See BlogView.urlpatterns for an example.

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I found that this pattern works for redirects and might help in your case (unless I am interpreting your question incorrectly). I couldn't reverse a pattern within the same tuple but if I defined a new tuple and then concatenated a new tuple to the original Djanogo would reflect without issue. ex:

  urlpatterns = patterns('',
         ('^foo/$','foo.views.foo')
  )
  urlpatterns+= patterns('',('^$','django.views.generic.simple.redirect_to',{'url':reverse('foo.views.foo')}))

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You can use a name to identify your url pattern like this:

urlpatterns = patterns('',
     url(repo_type_param + r'view-source' + opt_rev_param + path_param, view_source, name='myurlname'),
)

Note the url and name, and then reverse match like this:

reverse('myurlname', kwargs={'groupname': 'value'})

Hope it helps