small CR changes and doc updates

Author: dg-pb

Doc/library/functools.rst

@@ -373,20 +373,24 @@ The :mod:`functools` module defines the following functions:
    only one positional argument is provided, while there are two placeholders
    in :ref:`partial object <partial-objects>`.
 
-   When successively using :func:`partial` existing :data:`!Placeholder`
-   sentinels are filled first. A place for positional argument is retained
-   when :data:`!Placeholder` sentinel is replaced with a new one:
+   Successive :func:`partial` applications fill :data:`!Placeholder` sentinels
+   of the input :func:`partial` objects with new positional arguments.
+   A place for positional argument can be retained by inserting new
+   :data:`!Placeholder` sentinel to the place held by previous :data:`!Placeholder`:
 
       >>> from functools import partial, Placeholder as _
-      >>> count = partial(print, _, _, _, 4)
-      >>> count = partial(count, _, _, 3)
-      >>> count = partial(count, _, 2)
-      >>> count = partial(count, _, 5)   # 5 is appended after 4
-      >>> count(1)
+      >>> show5 = partial(print, _, _, _, 4)
+      >>> show5 = partial(show5, _, _, 3)
+      >>> show5 = partial(show5, _, 2)
+      >>> show5 = partial(show5, _, 5)   # 5 is appended after 4
+      >>> show5(1)
       1 2 3 4 5
 
+   Note, :data:`!Placeholder` has no special treatment when used for keyword
+   argument of :data:`!Placeholder`.
+
    .. versionchanged:: 3.14
-      Support for :data:`Placeholder` in *args*
+      Added support for :data:`Placeholder` in positional arguments.
 
 .. data:: Placeholder
 

Lib/test/test_functools.py

@@ -556,8 +556,8 @@ class TestPartialPySubclass(TestPartialPy):
     def test_subclass_optimization(self):
         p = py_functools.partial(min, 2)
         p2 = self.partial(p, 1)
-        assert p2.func is min
-        assert p2(0) == 0
+        self.assertIs(p2.func, min)
+        self.assertEqual(p2(0), 0)
 
 
 class TestPartialMethod(unittest.TestCase):
@@ -702,8 +702,8 @@ class PartialMethodSubclass(functools.partialmethod):
             pass
         p = functools.partialmethod(min, 2)
         p2 = PartialMethodSubclass(p, 1)
-        assert p2.func is min
-        assert p2.__get__(0)() == 0
+        self.assertIs(p2.func, min)
+        self.assertEqual(p2.__get__(0)(), 0)
 
 
 class TestUpdateWrapper(unittest.TestCase):

Modules/_functoolsmodule.c

@@ -150,14 +150,13 @@ partial_new(PyTypeObject *type, PyObject *args, PyObject *kw)
     PyObject *func, *pto_args, *new_args, *pto_kw;
     partialobject *pto;
     Py_ssize_t pto_phcount = 0;
-    Py_ssize_t new_nargs = PyTuple_GET_SIZE(args);
+    Py_ssize_t new_nargs = PyTuple_GET_SIZE(args) - 1;
 
-    if (new_nargs < 1) {
+    if (new_nargs < 0) {
         PyErr_SetString(PyExc_TypeError,
                         "type 'partial' takes at least one argument");
         return NULL;
     }
-    new_nargs--;
     func = PyTuple_GET_ITEM(args, 0);
     if (!PyCallable_Check(func)) {
         PyErr_SetString(PyExc_TypeError,
@@ -411,7 +410,7 @@ partial_vectorcall(partialobject *pto, PyObject *const *args,
         tot_nargs = pto_nargs + nargs - pto_phcount;
         Py_ssize_t j = 0;       // New args index
         for (Py_ssize_t i = 0; i < pto_nargs; i++) {
-            if (pto_args[i] == pto->placeholder){
+            if (pto_args[i] == pto->placeholder) {
                 stack[i] = args[j];
                 j += 1;
             }
@@ -500,6 +499,7 @@ partial_call(partialobject *pto, PyObject *args, PyObject *kwargs)
     if (pto_phcount) {
         Py_ssize_t pto_nargs = PyTuple_GET_SIZE(pto->args);
         Py_ssize_t tot_nargs = pto_nargs + nargs - pto_phcount;
+        assert(tot_nargs >= 0);
         tot_args = PyTuple_New(tot_nargs);
         if (tot_args == NULL) {
             Py_XDECREF(tot_kw);