From 59d127e45f5ed31e346162a0ac312f672c096821 Mon Sep 17 00:00:00 2001
From: Anton Baklanov <antonbaklanov@gmail.com>
Date: Wed, 17 Apr 2013 18:20:31 +0300
Subject: [PATCH] Fixed #20276 -- Implemented __bool__ for MergeDict

MergeDict evaluates now to False if all contained dicts are empty.
Thanks til for the report and the initial patch.
---
 django/utils/datastructures.py           | 6 ++++++
 tests/utils_tests/test_datastructures.py | 7 +++++++
 2 files changed, 13 insertions(+)

diff --git a/django/utils/datastructures.py b/django/utils/datastructures.py
index 64c218fe43..b3060202be 100644
--- a/django/utils/datastructures.py
+++ b/django/utils/datastructures.py
@@ -14,6 +14,12 @@ class MergeDict(object):
     def __init__(self, *dicts):
         self.dicts = dicts
 
+    def __bool__(self):
+        return any(self.dicts)
+
+    def __nonzero__(self):
+        return type(self).__bool__(self)
+
     def __getitem__(self, key):
         for dict_ in self.dicts:
             try:
diff --git a/tests/utils_tests/test_datastructures.py b/tests/utils_tests/test_datastructures.py
index 3161c04f97..91111cc2ed 100644
--- a/tests/utils_tests/test_datastructures.py
+++ b/tests/utils_tests/test_datastructures.py
@@ -203,6 +203,13 @@ class MergeDictTests(SimpleTestCase):
                            ('key2', ['value2', 'value3']),
                            ('key4', ['value5', 'value6'])])
 
+    def test_bool_casting(self):
+        empty = MergeDict({}, {}, {})
+        not_empty = MergeDict({}, {}, {"key": "value"})
+        self.assertFalse(empty)
+        self.assertTrue(not_empty)
+
+
 class MultiValueDictTests(SimpleTestCase):
 
     def test_multivaluedict(self):