From 49d6a82261feda6ee1bf23bb17184e932e232172 Mon Sep 17 00:00:00 2001
From: Jacob Kaplan-Moss <jacob@jacobian.org>
Date: Mon, 22 Feb 2010 23:34:33 +0000
Subject: [PATCH] Fixed #11687: the `add` filter is now less failsome when
 faced with things that can't be coerced to integers.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@12497 bcc190cf-cafb-0310-a4f2-bffc1f526a37
---
 django/template/defaultfilters.py          |  8 +++++++-
 docs/ref/templates/builtins.txt            | 21 +++++++++++++++++++++
 tests/regressiontests/templates/filters.py | 11 +++++++++++
 3 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/django/template/defaultfilters.py b/django/template/defaultfilters.py
index e6492dcd38..1f744f1958 100644
--- a/django/template/defaultfilters.py
+++ b/django/template/defaultfilters.py
@@ -651,7 +651,13 @@ unordered_list.needs_autoescape = True
 
 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):
diff --git a/docs/ref/templates/builtins.txt b/docs/ref/templates/builtins.txt
index b9fa99bf6f..aabacc5650 100644
--- a/docs/ref/templates/builtins.txt
+++ b/docs/ref/templates/builtins.txt
@@ -1010,6 +1010,27 @@ For example::
 
 If ``value`` is ``4``, then the output will be ``6``.
 
+.. versionchanged:: 1.2 
+   The following behavior didn't exist in previous Django versions.
+
+This filter will first try to coerce both values to integers. If this fails,
+it'll attempt to add the values together anyway. This will work on some data
+types (strings, list, etc.) and fail on others. If it fails, the result will
+be an empty string.
+
+For example, if we have::
+
+    {{ first|add:second }}
+
+and ``first`` is ``[1, 2, 3]`` and ``second`` is ``[4, 5, 6]``, then the
+output will be ``[1, 2, 3, 4, 5, 6]``.
+
+.. warning::
+    
+    Keep in mind that strings that can both be coerced to integers will be,
+    and thus will be will be *summed*, not concatenated, as in the first
+    example above.
+
 .. templatefilter:: addslashes
 
 addslashes
diff --git a/tests/regressiontests/templates/filters.py b/tests/regressiontests/templates/filters.py
index d2e8e7473b..c39e34b999 100644
--- a/tests/regressiontests/templates/filters.py
+++ b/tests/regressiontests/templates/filters.py
@@ -333,4 +333,15 @@ def get_filter_tests():
         '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'),
     }