python · serhiy-storchaka · Feb 22, 2017 · Feb 21, 2017 · Feb 21, 2017
diff --git a/Lib/test/test_functools.py b/Lib/test/test_functools.py
@@ -80,6 +80,15 @@ 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

diff --git 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
@@ -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);