bpo-34320: Fix dict(o) didn't copy order of dict subclass (GH-8624)

When dict subclass overrides order (`__iter__()`, `keys()`, and `items()`), `dict(o)`
should use it instead of dict ordering.


https://bugs.python.org/issue34320

Author: methane

Lib/test/test_builtin.py

@@ -1968,6 +1968,15 @@ class B:
         with self.assertRaises(TypeError):
             type('A', (B,), {'__slots__': '__weakref__'})
 
+    def test_namespace_order(self):
+        # bpo-34320: namespace should preserve order
+        od = collections.OrderedDict([('a', 1), ('b', 2)])
+        od.move_to_end('a')
+        expected = list(od.items())
+
+        C = type('C', (), od)
+        self.assertEqual(list(C.__dict__.items())[:2], [('b', 2), ('a', 1)])
+
 
 def load_tests(loader, tests, pattern):
     from doctest import DocTestSuite

Lib/test/test_call.py

@@ -9,6 +9,23 @@
 import collections
 import itertools
 
+
+class FunctionCalls(unittest.TestCase):
+
+    def test_kwargs_order(self):
+        # bpo-34320:  **kwargs should preserve order of passed OrderedDict
+        od = collections.OrderedDict([('a', 1), ('b', 2)])
+        od.move_to_end('a')
+        expected = list(od.items())
+
+        def fn(**kw):
+            return kw
+
+        res = fn(**od)
+        self.assertIsInstance(res, dict)
+        self.assertEqual(list(res.items()), expected)
+
+
 # The test cases here cover several paths through the function calling
 # code.  They depend on the METH_XXX flag that is used to define a C
 # function, which can't be verified from Python.  If the METH_XXX decl

Lib/test/test_dict.py

@@ -1222,6 +1222,36 @@ def iter_and_mutate():
 
         self.assertRaises(RuntimeError, iter_and_mutate)
 
+    def test_dict_copy_order(self):
+        # bpo-34320
+        od = collections.OrderedDict([('a', 1), ('b', 2)])
+        od.move_to_end('a')
+        expected = list(od.items())
+
+        copy = dict(od)
+        self.assertEqual(list(copy.items()), expected)
+
+        # dict subclass doesn't override __iter__
+        class CustomDict(dict):
+            pass
+
+        pairs = [('a', 1), ('b', 2), ('c', 3)]
+
+        d = CustomDict(pairs)
+        self.assertEqual(pairs, list(dict(d).items()))
+
+        class CustomReversedDict(dict):
+            def keys(self):
+                return reversed(list(dict.keys(self)))
+
+            __iter__ = keys
+
+            def items(self):
+                return reversed(dict.items(self))
+
+        d = CustomReversedDict(pairs)
+        self.assertEqual(pairs[::-1], list(dict(d).items()))
+
 
 class CAPITest(unittest.TestCase):
 

Misc/NEWS.d/next/Core and Builtins/2018-08-02-22-34-59.bpo-34320.hNshAA.rst

@@ -0,0 +1 @@
+Fix ``dict(od)`` didn't copy iteration order of OrderedDict.

Objects/dictobject.c

@@ -235,6 +235,8 @@ static Py_ssize_t lookdict_split(PyDictObject *mp, PyObject *key,
 
 static int dictresize(PyDictObject *mp, Py_ssize_t minused);
 
+static PyObject* dict_iter(PyDictObject *dict);
+
 /*Global counter used to set ma_version_tag field of dictionary.
  * It is incremented each time that a dictionary is created and each
  * time that a dictionary is modified. */
@@ -2379,7 +2381,7 @@ dict_merge(PyObject *a, PyObject *b, int override)
         return -1;
     }
     mp = (PyDictObject*)a;
-    if (PyDict_Check(b)) {
+    if (PyDict_Check(b) && (Py_TYPE(b)->tp_iter == (getiterfunc)dict_iter)) {
         other = (PyDictObject*)b;
         if (other == mp || other->ma_used == 0)
             /* a.update(a) or a.update({}); nothing to do */