From 96c9e12f7ff9607a35b75bee56ee87edabc8dbb7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Sybren=20A=2E=20St=C3=BCvel?= <sybren@stuvel.eu>
Date: Wed, 12 Oct 2016 17:09:48 +0200
Subject: [PATCH] doc_diff() optionally no longer reports differences between
 falsey values.

If falsey_is_equal=True, all Falsey values compare as equal, i.e. this
function won't report differences between DoesNotExist, False, '', and 0.
---
 pillar/api/utils/__init__.py | 15 ++++++++++++++-
 tests/test_api/test_utils.py | 21 +++++++++++++++++++++
 2 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/pillar/api/utils/__init__.py b/pillar/api/utils/__init__.py
index 00f64696..c096cc08 100644
--- a/pillar/api/utils/__init__.py
+++ b/pillar/api/utils/__init__.py
@@ -115,11 +115,19 @@ def gravatar(email, size=64):
            "?" + urllib.urlencode(parameters)
 
 
+
+class MetaFalsey(type):
+    def __nonzero__(cls):
+        return False
+    __bool__ = __nonzero__  # for Python 3
+
+
 class DoesNotExist(object):
     """Returned as value by doc_diff if a value does not exist."""
+    __metaclass__ = MetaFalsey
 
 
-def doc_diff(doc1, doc2):
+def doc_diff(doc1, doc2, falsey_is_equal=True):
     """Generator, yields differences between documents.
 
     Yields changes as (key, value in doc1, value in doc2) tuples, where
@@ -128,6 +136,9 @@ def doc_diff(doc1, doc2):
 
     Sub-documents (i.e. dicts) are recursed, and dot notation is used
     for the keys if changes are found.
+
+    If falsey_is_equal=True, all Falsey values compare as equal, i.e. this
+    function won't report differences between DoesNotExist, False, '', and 0.
     """
 
     for key in set(doc1.keys()).union(set(doc2.keys())):
@@ -145,5 +156,7 @@ def doc_diff(doc1, doc2):
 
         if val1 == val2:
             continue
+        if falsey_is_equal and bool(val1) == bool(val2) == False:
+            continue
 
         yield key, val1, val2
diff --git a/tests/test_api/test_utils.py b/tests/test_api/test_utils.py
index f4dc4f65..3b8d56d0 100644
--- a/tests/test_api/test_utils.py
+++ b/tests/test_api/test_utils.py
@@ -54,6 +54,27 @@ class DocDiffTest(unittest.TestCase):
 
         self.assertEqual([(3, 42, 513)], list(diff))
 
+    def test_diff_values_falsey(self):
+        from pillar.api.utils import doc_diff, DoesNotExist
+
+        # DoesNotExist vs. empty string
+        diff = doc_diff({'a': 'b', 3: ''},
+                        {'a': 'b'})
+        self.assertEqual([], list(diff))
+
+        diff = doc_diff({'a': 'b', 3: ''},
+                        {'a': 'b'}, falsey_is_equal=False)
+        self.assertEqual([(3, '', DoesNotExist)], list(diff))
+
+        # Empty string vs. None
+        diff = doc_diff({'a': 'b', 3: ''},
+                        {'a': 'b', 3: None})
+        self.assertEqual([], list(diff))
+
+        diff = doc_diff({'a': 'b', 3: ''},
+                        {'a': 'b', 3: None}, falsey_is_equal=False)
+        self.assertEqual([(3, '', None)], list(diff))
+
     def test_diff_keys_simple(self):
         from pillar.api.utils import doc_diff, DoesNotExist
         diff = doc_diff({'a': 'b', 3: 42},