bpo-29532: Altering a kwarg dictionary passed to functools.partial() (p…

…ython#190)

no longer affects a partial object after creation.
(cherry picked from commit 9639e4a)

Lib/test/test_functools.py

@@ -89,6 +89,15 @@ def func(a=10, b=20):
         p(b=7)
         self.assertEqual(d, {'a':3})
 
+    def test_kwargs_copy(self):
+        # Issue #29532: Altering a kwarg dictionary passed to a constructor
+        # should not affect a partial object after creation
+        d = {'a': 3}
+        p = self.partial(capture, **d)
+        self.assertEqual(p(), ((), {'a': 3}))
+        d['a'] = 5
+        self.assertEqual(p(), ((), {'a': 3}))
+
     def test_arg_combinations(self):
         # exercise special code paths for zero args in either partial
         # object or the caller

Modules/_functoolsmodule.c

@@ -88,10 +88,13 @@ partial_new(PyTypeObject *type, PyObject *args, PyObject *kw)
         if (kw == NULL) {
             pto->kw = PyDict_New();
         }
-        else {
+        else if (Py_REFCNT(kw) == 1) {
             Py_INCREF(kw);
             pto->kw = kw;
         }
+        else {
+            pto->kw = PyDict_Copy(kw);
+        }
     }
     else {
         pto->kw = PyDict_Copy(pkw);