PYTHON-977 - Fix __hash__ method on BSON types that inherit from Python builtin types.

In Python 2, objects automatically inherit the __hash__ of their parent
class. In Python 3, objects that override __eq__ do not automatically inherit
__hash__, so these objects were not hashable under Python 3.  Additionally,
mutable BSON types and types that overide __eq__ but did not explicitly define
__hash__ had broken __hash__ methods under Python 2.  This commit unifies the
hashing behavior between Python versions and fixes the __hash__ methods such
that two BSON objects hash the same only if they are equal.

N.B.: bson.code.Code and bson.regex.Regex are no longer hashable under Python 2
because they are mutable.

bson/binary.py

@@ -171,6 +171,9 @@ class Binary(bytes):
         # subclass of str...
         return False
 
+    def __hash__(self):
+        return super(Binary, self).__hash__() ^ hash(self.__subtype)
+
     def __ne__(self, other):
         return not self == other
 

bson/code.py

@@ -77,5 +77,7 @@ class Code(str):
             return (self.__scope, str(self)) == (other.__scope, str(other))
         return False
 
+    __hash__ = None
+
     def __ne__(self, other):
         return not self == other

bson/max_key.py

@@ -28,6 +28,9 @@ class MaxKey(object):
     def __eq__(self, other):
         return isinstance(other, MaxKey)
 
+    def __hash__(self):
+        return hash(self._type_marker)
+
     def __ne__(self, other):
         return not self == other
 

bson/min_key.py

@@ -28,6 +28,9 @@ class MinKey(object):
     def __eq__(self, other):
         return isinstance(other, MinKey)
 
+    def __hash__(self):
+        return hash(self._type_marker)
+
     def __ne__(self, other):
         return not self == other
     

bson/regex.py

@@ -104,6 +104,8 @@ class Regex(object):
         else:
             return NotImplemented
 
+    __hash__ = None
+
     def __ne__(self, other):
         return not self == other
 

bson/timestamp.py

@@ -23,6 +23,7 @@ from bson.tz_util import utc
 
 UPPERBOUND = 4294967296
 
+
 class Timestamp(object):
     """MongoDB internal timestamps used in the opLog.
     """
@@ -81,6 +82,9 @@ class Timestamp(object):
         else:
             return NotImplemented
 
+    def __hash__(self):
+        return hash(self.time) ^ hash(self.inc)
+
     def __ne__(self, other):
         return not self == other
 

test/test_binary.py

@@ -129,6 +129,13 @@ class TestBinary(unittest.TestCase):
         self.assertEqual(repr(five),
                          "Binary(%s, 100)" % (repr(b"test"),))
 
+    def test_hash(self):
+        one = Binary(b"hello world")
+        two = Binary(b"hello world", 42)
+        self.assertEqual(hash(Binary(b"hello world")), hash(one))
+        self.assertNotEqual(hash(one), hash(two))
+        self.assertEqual(hash(Binary(b"hello world", 42)), hash(two))
+
     def test_legacy_java_uuid(self):
         # Test decoding
         data = self.java_data

test/test_bson.py

@@ -759,6 +759,9 @@ class TestBSON(unittest.TestCase):
         unicode_regex = re.compile('', re.U)
         self.assertEqual(re.U, Regex.from_native(unicode_regex).flags)
 
+    def test_regex_hash(self):
+        self.assertRaises(TypeError, hash, Regex('hello'))
+
     def test_exception_wrapping(self):
         # No matter what exception is raised while trying to decode BSON,
         # the final exception always matches InvalidBSON.
@@ -815,6 +818,11 @@ class TestBSON(unittest.TestCase):
         self.assertTrue(MaxKey() != MinKey())
         self.assertFalse(MaxKey() == MinKey())
 
+    def test_minkey_maxkey_hash(self):
+        self.assertEqual(hash(MaxKey()), hash(MaxKey()))
+        self.assertEqual(hash(MinKey()), hash(MinKey()))
+        self.assertNotEqual(hash(MaxKey()), hash(MinKey()))
+
     def test_timestamp_comparison(self):
         # Timestamp is initialized with time, inc. Time is the more
         # significant comparand.

test/test_code.py

@@ -77,6 +77,9 @@ class TestCode(unittest.TestCase):
         self.assertFalse(b != Code("hello"))
         self.assertFalse(b != Code("hello", {}))
 
+    def test_hash(self):
+        self.assertRaises(TypeError, hash, Code("hello world"))
+
     def test_scope_preserved(self):
         a = Code("hello")
         b = Code("hello", {"foo": 5})

test/test_timestamp.py

@@ -69,6 +69,11 @@ class TestTimestamp(unittest.TestCase):
         # Explicitly test inequality
         self.assertFalse(t != Timestamp(1, 1))
 
+    def test_hash(self):
+        self.assertEqual(hash(Timestamp(1, 2)), hash(Timestamp(1, 2)))
+        self.assertNotEqual(hash(Timestamp(1, 2)), hash(Timestamp(1, 3)))
+        self.assertNotEqual(hash(Timestamp(1, 2)), hash(Timestamp(2, 2)))
+
     def test_repr(self):
         t = Timestamp(0, 0)
         self.assertEqual(repr(t), "Timestamp(0, 0)")