Template tag can now optionally return a default value when reverse r…

…aises NoReverseMatch

aldryn_apphooks_config/templatetags/apphooks_config_tags.py

@@ -6,6 +6,7 @@
 
 from django import template
 from django.core import urlresolvers
+from django.core.urlresolvers import NoReverseMatch
 
 from ..utils import get_app_instance
 
@@ -17,10 +18,17 @@
 def namespace_url(context, view_name, *args, **kwargs):
     """
     Returns an absolute URL matching named view with its parameters and the
-    provided application instance namespace. If no namespace is passed as a
-    kwarg (or it is "" or None), this templatetag will look into the request
-    object for the app_config's namespace. If there is still no namespace found,
-    this tag will act like the normal {% url ... %} tag.
+    provided application instance namespace.
+
+    If no namespace is passed as a kwarg (or it is "" or None), this templatetag
+    will look into the request object for the app_config's namespace. If there
+    is still no namespace found, this tag will act like the normal {% url ... %}
+    template tag.
+
+    Normally, this tag will return whatever is returned by the ultimate call to
+    reverse, which also means it will raise NoReverseMatch if reverse() cannot
+    find a match. This behaviour can be override by suppling a 'default' kwarg
+    with the value of what should be returned when no match is found.
     """
 
     namespace = kwargs.pop('namespace', None)
@@ -31,11 +39,26 @@ def namespace_url(context, view_name, *args, **kwargs):
     if namespace:
         namespace += ":"
 
-    reverse = partial(urlresolvers.reverse, '{0:s}{1:s}'.format(namespace, view_name))
+    reverse = partial(
+        urlresolvers.reverse, '{0:s}{1:s}'.format(namespace, view_name))
 
-    if kwargs:
-        return reverse(kwargs=kwargs)
-    elif args:
-        return reverse(args=args)
-    else:
-        return reverse()
+    # We're explicitly NOT happy to just re-raise the exception, as that may
+    # adversely affect stack traces.
+    if 'default' not in kwargs:
+        if kwargs:
+            return reverse(kwargs=kwargs)
+        elif args:
+            return reverse(args=args)
+        else:
+            return reverse()
+
+    default = kwargs.pop('default', None)
+    try:
+        if kwargs:
+            return reverse(kwargs=kwargs)
+        elif args:
+            return reverse(args=args)
+        else:
+            return reverse()
+    except NoReverseMatch:
+        return default