Джанго необязательный параметр пути
urlpatterns = patterns('',
url(r'^project_config/$', views.foo),
url(r'^project_config/(?P<product>\w+)/$', views.foo),
url(r'^project_config/(?P<product>\w+)/(?P<project_id>\w+)/$', views.foo),
)
Enthusiastic Elephant