Note that we can't preserve key order in json_util.dumps in Python 2.4, PYTHON-602.

bson/json_util.py

@@ -47,6 +47,10 @@ It won't handle :class:`~bson.binary.Binary` and :class:`~bson.code.Code`
 instances (as they are extended strings you can't provide custom defaults),
 but it will be faster as there is less recursion.
 
+.. versionchanged:: 2.7
+   Preserves order when rendering SON, Timestamp, Code, Binary, and DBRef
+   instances. (But not in Python 2.4.)
+
 .. versionchanged:: 2.3
    Added dumps and loads helpers to automatically handle conversion to and
    from json and supports :class:`~bson.binary.Binary` and
@@ -114,7 +118,7 @@ def dumps(obj, *args, **kwargs):
 
     .. versionchanged:: 2.7
        Preserves order when rendering SON, Timestamp, Code, Binary, and DBRef
-       instances.
+       instances. (But not in Python 2.4.)
     """
     if not json_lib:
         raise Exception("No json library available")
@@ -193,6 +197,14 @@ def object_hook(dct, compile_re=True):
 
 
 def default(obj):
+    # We preserve key order when rendering SON, DBRef, etc. as JSON by
+    # returning a SON for those types instead of a dict. This works with
+    # the "json" standard library in Python 2.6+ and with simplejson
+    # 2.1.0+ in Python 2.5+, because those libraries iterate the SON
+    # using PyIter_Next. Python 2.4 must use simplejson 2.0.9 or older,
+    # and those versions of simplejson use the lower-level PyDict_Next,
+    # which bypasses SON's order-preserving iteration, so we lose key
+    # order in Python 2.4.
     if isinstance(obj, ObjectId):
         return {"$oid": str(obj)}
     if isinstance(obj, DBRef):

test/test_json_util.py

@@ -40,6 +40,7 @@ from bson.tz_util import utc
 from test.test_client import get_client
 
 PY3 = sys.version_info[0] == 3
+PY24 = sys.version_info[:2] == (2, 4)
 
 
 class TestJsonUtil(unittest.TestCase):
@@ -70,10 +71,11 @@ class TestJsonUtil(unittest.TestCase):
         self.round_trip({"ref": DBRef("foo", 5, "db")})
         self.round_trip({"ref": DBRef("foo", ObjectId())})
 
-        # Check order.
-        self.assertEqual(
-            '{"$ref": "collection", "$id": 1, "$db": "db"}',
-            json_util.dumps(DBRef('collection', 1, 'db')))
+        if not PY24:
+            # Check order.
+            self.assertEqual(
+                '{"$ref": "collection", "$id": 1, "$db": "db"}',
+                json_util.dumps(DBRef('collection', 1, 'db')))
 
     def test_datetime(self):
         # only millis, not micros
@@ -130,14 +132,15 @@ class TestJsonUtil(unittest.TestCase):
                 '{"r": {"$regex": ".*", "$options": "ilm"}}',
                 compile_re=False)['r'])
 
-        # Check order.
-        self.assertEqual(
-            '{"$regex": ".*", "$options": "mx"}',
-            json_util.dumps(Regex('.*', re.M | re.X)))
+        if not PY24:
+            # Check order.
+            self.assertEqual(
+                '{"$regex": ".*", "$options": "mx"}',
+                json_util.dumps(Regex('.*', re.M | re.X)))
 
-        self.assertEqual(
-            '{"$regex": ".*", "$options": "mx"}',
-            json_util.dumps(re.compile(b('.*'), re.M | re.X)))
+            self.assertEqual(
+                '{"$regex": ".*", "$options": "mx"}',
+                json_util.dumps(re.compile(b('.*'), re.M | re.X)))
 
     def test_minkey(self):
         self.round_trip({"m": MinKey()})
@@ -146,10 +149,12 @@ class TestJsonUtil(unittest.TestCase):
         self.round_trip({"m": MaxKey()})
 
     def test_timestamp(self):
-        res = json_util.json.dumps({"ts": Timestamp(4, 13)},
-                                     default=json_util.default)
-        self.assertEqual('{"ts": {"t": 4, "i": 13}}', res)
-        dct = json_util.json.loads(res)
+        res = json_util.dumps({"ts": Timestamp(4, 13)}, default=json_util.default)
+        if not PY24:
+            # Check order.
+            self.assertEqual('{"ts": {"t": 4, "i": 13}}', res)
+
+        dct = json_util.loads(res)
         self.assertEqual(dct['ts']['t'], 4)
         self.assertEqual(dct['ts']['i'], 13)
 
@@ -178,9 +183,12 @@ class TestJsonUtil(unittest.TestCase):
             json_util.loads('{"bin": {"$type": 0, "$binary": "AAECAwQ="}}'))
 
         json_bin_dump = json_util.dumps(md5_type_dict)
-        self.assertEqual(
-            '{"md5": {"$binary": "IG43GK8JL9HRL4DK53HMrA==", "$type": "05"}}',
-            json_bin_dump)
+        if not PY24:
+            # Check order.
+            self.assertEqual(
+                '{"md5": {"$binary": "IG43GK8JL9HRL4DK53HMrA==",'
+                + ' "$type": "05"}}',
+                json_bin_dump)
 
         self.assertEqual(md5_type_dict,
             json_util.loads('{"md5": {"$type": 5, "$binary":'
@@ -208,8 +216,9 @@ class TestJsonUtil(unittest.TestCase):
         res = json_util.dumps(code)
         self.assertEqual(code, json_util.loads(res))
 
-        # Check order.
-        self.assertEqual('{"$code": "return z", "$scope": {"z": 2}}', res)
+        if not PY24:
+            # Check order.
+            self.assertEqual('{"$code": "return z", "$scope": {"z": 2}}', res)
 
     def test_cursor(self):
         db = self.db