Ticket #11687: add_filter.diff

django/template/defaultfilters.py

@@ -649 +649 @@
 
 def add(value, arg):
     """Adds the arg to the value."""
-    return int(value) + int(arg)
+    try:
+        return int(value) + int(arg)
+    except (ValueError, TypeError):
+        try:
+            return value + arg
+        except:
+            return value
 add.is_safe = False
 
 def get_digit(value, arg):

tests/regressiontests/templates/filters.py

@@ -326 +326 @@
         'date02': (r'{{ d|date }}', {'d': datetime(2008, 1, 1)}, 'Jan. 1, 2008'),
         #Ticket 9520: Make sure |date doesn't blow up on non-dates
         'date03': (r'{{ d|date:"m" }}', {'d': 'fail_string'}, ''),
+        
+         # base tests for add that assert, that old behaviour, which means
+         # trying to add two values as ints, is kept
+         'add01': (r'{{ i|add:"5" }}', {'i': 2000}, '2005'),
+         'add02': (r'{{ i|add:"napis" }}', {'i': 2000}, '2000'),
+         'add03': (r'{{ i|add:16 }}', {'i': 'not_an_int'}, 'not_an_int'),
+         'add04': (r'{{ i|add:"16" }}', {'i': 'not_an_int'}, 'not_an_int16'),
+         # further additions using dynamic typing
+         'add05': (r'{{ l1|add:l2 }}', {'l1': [1, 2], 'l2': [3, 4]}, '[1, 2, 3, 4]'),
+         'add06': (r'{{ t1|add:t2 }}', {'t1': (3, 4), 't2': (1, 2)}, '(3, 4, 1, 2)'),
+         'add07': (r'{{ d|add:t }}', {'d': date(2000, 1, 1), 't': timedelta(10)}, '2000-01-11'),
     }

docs/ref/templates/builtins.txt

@@ -858 +858 @@
 
 If ``value`` is ``4``, then the output will be ``6``.
 
+.. versionadded:: 1.2
+
+At first filter tries to add two values coerced into integers and if this fails, it adds those two values using duck typing. 
+
+For example:
+
+    {{ first_list|add:second_list }}
+    
+If ``first_list`` is ``[1, 2, 3]`` and ``second_list`` is ``[4, 5, 6]``, then the output will be ``[1, 2, 3, 4, 5, 6]``.
+
+Keep in mind, that for two strings, that can be coerced to integer, it will return a sum, rather than 
+a concatenation, as in the first example.
+
 .. templatefilter:: addslashes
 
 addslashes