[3.5] bpo-29532: Altering a kwarg dictionary passed to functools.partial() no longer affects a partial object after creation. (#222)

3 files changed, 16 insertions, 1 deletions

diff --git a/Lib/test/test_functools.py b/Lib/test/test_functools.py
index 9ccd0ca..a82ca7a 100644
--- a/Lib/test/test_functools.py
+++ b/Lib/test/test_functools.py
@@ -80,6 +80,15 @@ class TestPartial:
         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
diff --git a/Misc/NEWS b/Misc/NEWS
index 0382337..a01d454 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -32,6 +32,9 @@ Extension Modules
 Library
 -------
 
+- bpo-29532: Altering a kwarg dictionary passed to functools.partial()
+  no longer affects a partial object after creation.
+
 - Issue #28556: Various updates to typing module: typing.Counter, typing.ChainMap,
   improved ABC caching, etc. Original PRs by Jelle Zijlstra, Ivan Levkivskyi,
   Manuel Krebber, and Łukasz Langa.
diff --git a/Modules/_functoolsmodule.c b/Modules/_functoolsmodule.c
index be0f5f9..0471d66 100644
--- a/Modules/_functoolsmodule.c
+++ b/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);