ensure group_name is an str, and not a translated string, keep pattern instance

basetheme_bootstrap/templatetags/basetheme_bootstrap.py

@@ -45,10 +45,13 @@ def tags_to_bootstrap(tag):
     return tag
 
 
+__group_name_to_id__pattern = re.compile('[\W_]+')
+
+
 @register.filter
 def group_name_to_id(group_name):
-    pattern = re.compile('[\W_]+')
-    return pattern.sub('', group_name)
+    return __group_name_to_id__pattern.sub('', str(group_name))
+
 
 class IncludeIfExistsNode(template.Node):
     """