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gh-128644: functools.partial: Allowing trailing Placeholders #128649

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gh-128644: functools.partial: Allowing trailing Placeholders #128649

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3afb960
impl
dg-pb Jan 8, 2025
3c60fdf
📜🤖 Added by blurb_it.
blurb-it[bot] Jan 8, 2025
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12 changes: 9 additions & 3 deletions Lib/functools.py
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Original file line number Diff line number Diff line change
Expand Up @@ -307,7 +307,15 @@ def _partial_prepare_merger(args):
else:
order.append(i)
phcount = j - nargs
merger = itemgetter(*order) if phcount else None
if phcount:
if nargs == 1:
i = order[0]
def merger(all_args):
return (all_args[i],)
else:
merger = itemgetter(*order)
else:
merger = None
return phcount, merger

def _partial_new(cls, func, /, *args, **keywords):
Expand All @@ -321,8 +329,6 @@ def _partial_new(cls, func, /, *args, **keywords):
if not callable(func) and not hasattr(func, "__get__"):
raise TypeError(f"the first argument {func!r} must be a callable "
"or a descriptor")
if args and args[-1] is Placeholder:
raise TypeError("trailing Placeholders are not allowed")
if isinstance(func, base_cls):
pto_phcount = func._phcount
tot_args = func.args
Expand Down
30 changes: 20 additions & 10 deletions Lib/test/test_functools.py
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Expand Up @@ -211,11 +211,27 @@ def foo(bar):
p2.new_attr = 'spam'
self.assertEqual(p2.new_attr, 'spam')

def test_placeholders_trailing_raise(self):
def test_trailing_placeholders(self):
PH = self.module.Placeholder
for args in [(PH,), (0, PH), (0, PH, 1, PH, PH, PH)]:
with self.assertRaises(TypeError):
self.partial(capture, *args)
partial = self.partial

# Single Placeholder
p = partial(capture, PH)
actual_args, actual_kwds = p(0)
self.assertEqual(actual_args, (0,))
self.assertEqual(actual_kwds, {})

# 2 arg trailing Placeholder
p = partial(capture, 0, PH)
actual_args, actual_kwds = p(1)
self.assertEqual(actual_args, (0, 1))
self.assertEqual(actual_kwds, {})

# Complex case
p = partial(capture, 0, PH, 2, PH, PH)
actual_args, actual_kwds = p(1, 3, 4)
self.assertEqual(actual_args, (0, 1, 2, 3, 4))
self.assertEqual(actual_kwds, {})

def test_placeholders(self):
PH = self.module.Placeholder
Expand Down Expand Up @@ -368,12 +384,6 @@ def test_setstate(self):
f()
self.assertEqual(f(2), ((2, 1), dict(a=10)))

# Trailing Placeholder error
f = self.partial(signature)
msg_regex = re.escape("trailing Placeholders are not allowed")
with self.assertRaisesRegex(TypeError, f'^{msg_regex}$') as cm:
f.__setstate__((capture, (1, PH), dict(a=10), dict(attr=[])))

def test_setstate_errors(self):
f = self.partial(signature)
self.assertRaises(TypeError, f.__setstate__, (capture, (), {}))
Expand Down
1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Library/2025-01-08-20-40-38.gh-issue-128644.3pWHOQ.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
:func:`functools.partial` now allows trailing placeholders, which are converted to positional-only arguments.
123 changes: 69 additions & 54 deletions Modules/_functoolsmodule.c
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Original file line number Diff line number Diff line change
Expand Up @@ -189,13 +189,6 @@ partial_new(PyTypeObject *type, PyObject *args, PyObject *kw)
}
phold = state->placeholder;

/* Placeholder restrictions */
if (new_nargs && PyTuple_GET_ITEM(args, new_nargs) == phold) {
PyErr_SetString(PyExc_TypeError,
"trailing Placeholders are not allowed");
return NULL;
}

/* check wrapped function / object */
pto_args = pto_kw = NULL;
int res = PyObject_TypeCheck(func, state->partial_type);
Expand Down Expand Up @@ -229,55 +222,76 @@ partial_new(PyTypeObject *type, PyObject *args, PyObject *kw)
return NULL;
}

/* Count placeholders */
Py_ssize_t phcount = 0;
for (Py_ssize_t i = 0; i < new_nargs - 1; i++) {
if (PyTuple_GET_ITEM(new_args, i) == phold) {
phcount++;
/* process args */
if (new_nargs == 0) {
if (pto_args == NULL) {
pto->args = PyTuple_New(0);
pto->phcount = 0;
}
else {
pto->args = pto_args;
pto->phcount = pto_phcount;
Py_INCREF(pto_args);
assert(PyTuple_Check(pto->args));
}
}
/* merge args with args of `func` which is `partial` */
if (pto_phcount > 0 && new_nargs > 0) {
Py_ssize_t npargs = PyTuple_GET_SIZE(pto_args);
Py_ssize_t tot_nargs = npargs;
if (new_nargs > pto_phcount) {
tot_nargs += new_nargs - pto_phcount;
else {
/* Count placeholders */
Py_ssize_t phcount = 0;
for (Py_ssize_t i = 0; i < new_nargs; i++) {
if (PyTuple_GET_ITEM(args, i + 1) == phold) {
phcount++;
}
}
PyObject *item;
PyObject *tot_args = PyTuple_New(tot_nargs);
for (Py_ssize_t i = 0, j = 0; i < tot_nargs; i++) {
if (i < npargs) {
item = PyTuple_GET_ITEM(pto_args, i);
if (j < new_nargs && item == phold) {
item = PyTuple_GET_ITEM(new_args, j);
j++;
pto_phcount--;
if (pto_args == NULL) {
new_args = PyTuple_GetSlice(args, 1, new_nargs + 1);
if (new_args == NULL) {
Py_DECREF(pto);
return NULL;
}
pto->args = new_args;
pto->phcount = phcount;
}
else {
/* merge args with args of `func` which is `partial` */
Py_ssize_t npargs = PyTuple_GET_SIZE(pto_args);
Py_ssize_t tot_nargs = npargs;
if (new_nargs > pto_phcount) {
tot_nargs += new_nargs - pto_phcount;
}
PyObject *tot_args = PyTuple_New(tot_nargs);
PyObject *item;
if (pto_phcount > 0) {
for (Py_ssize_t i = 0, j = 0; i < tot_nargs; ++i) {
if (i < npargs) {
item = PyTuple_GET_ITEM(pto_args, i);
if (j < new_nargs && item == phold) {
item = PyTuple_GET_ITEM(args, j + 1);
j++;
pto_phcount--;
}
}
else {
item = PyTuple_GET_ITEM(args, j + 1);
j++;
}
PyTuple_SET_ITEM(tot_args, i, Py_NewRef(item));
}
}
else {
item = PyTuple_GET_ITEM(new_args, j);
j++;
for (Py_ssize_t i = 0; i < npargs; ++i) {
item = PyTuple_GET_ITEM(pto_args, i);
PyTuple_SET_ITEM(tot_args, i, Py_NewRef(item));
}
for (Py_ssize_t i = 0; i < new_nargs; ++i) {
item = PyTuple_GET_ITEM(args, i + 1);
PyTuple_SET_ITEM(tot_args, npargs + i, Py_NewRef(item));
}
}
Py_INCREF(item);
PyTuple_SET_ITEM(tot_args, i, item);
}
pto->args = tot_args;
pto->phcount = pto_phcount + phcount;
Py_DECREF(new_args);
}
else if (pto_args == NULL) {
pto->args = new_args;
pto->phcount = phcount;
}
else {
pto->args = PySequence_Concat(pto_args, new_args);
pto->phcount = pto_phcount + phcount;
Py_DECREF(new_args);
if (pto->args == NULL) {
Py_DECREF(pto);
return NULL;
pto->args = tot_args;
pto->phcount = pto_phcount + phcount;
assert(PyTuple_Check(pto->args));
}
assert(PyTuple_Check(pto->args));
}

if (pto_kw == NULL || PyDict_GET_SIZE(pto_kw) == 0) {
Expand Down Expand Up @@ -402,6 +416,12 @@ partial_vectorcall(PyObject *self, PyObject *const *args,
pto_args, pto_nargs, NULL);
}

/* Fast path if pto_args are all Placeholders */
if (pto_nargs == pto_phcount) {
return _PyObject_VectorcallTstate(tstate, pto->fn,
args, nargs, kwnames);
}

/* Fast path using PY_VECTORCALL_ARGUMENTS_OFFSET to prepend a single
* positional argument */
if (pto_nargs == 1 && (nargsf & PY_VECTORCALL_ARGUMENTS_OFFSET)) {
Expand Down Expand Up @@ -693,13 +713,8 @@ partial_setstate(PyObject *self, PyObject *state)
return NULL;
}

Py_ssize_t nargs = PyTuple_GET_SIZE(fnargs);
if (nargs && PyTuple_GET_ITEM(fnargs, nargs - 1) == pto->placeholder) {
PyErr_SetString(PyExc_TypeError,
"trailing Placeholders are not allowed");
return NULL;
}
/* Count placeholders */
Py_ssize_t nargs = PyTuple_GET_SIZE(fnargs);
Py_ssize_t phcount = 0;
for (Py_ssize_t i = 0; i < nargs - 1; i++) {
if (PyTuple_GET_ITEM(fnargs, i) == pto->placeholder) {
Expand Down
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