use PyObject_TypeCheck in the C implementation of partial.__new__

cfbolz · cfbolz · commit 97b9966bc7bb · 2022-12-14T17:30:45.000+01:00
diff --git a/Lib/functools.py b/Lib/functools.py
@@ -284,7 +284,7 @@ def __new__(cls, func, /, *args, **keywords):
         if not callable(func):
             raise TypeError("the first argument must be callable")
 
-        if isinstance(func, partial) and hasattr(func, "func"):
+        if isinstance(func, partial):
             args = func.args + args
             keywords = {**func.keywords, **keywords}
             func = func.func
diff --git a/Misc/NEWS.d/next/Library/2022-12-14-15-53-38.gh-issue-100242.Ny7VUO.rst b/Misc/NEWS.d/next/Library/2022-12-14-15-53-38.gh-issue-100242.Ny7VUO.rst
@@ -1,3 +1,5 @@
 Bring pure Python implementation ``functools.partial.__new__`` more in line
 with the C-implementation by not just always checking for the presence of
-the attribute ``'func'`` on the first argument of ``partial``.
+the attribute ``'func'`` on the first argument of ``partial``. Instead, both
+the Python version and the C version perform an ``isinstance(func, partial)``
+check on the first argument of ``partial``.
diff --git a/Modules/_functoolsmodule.c b/Modules/_functoolsmodule.c
@@ -79,12 +79,19 @@ partial_new(PyTypeObject *type, PyObject *args, PyObject *kw)
         return NULL;
     }
 
+    _functools_state *state = get_functools_state_by_type(type);
+    if (state == NULL) {
+        return NULL;
+    }
+
     pargs = pkw = NULL;
     func = PyTuple_GET_ITEM(args, 0);
-    if (Py_TYPE(func)->tp_call == (ternaryfunc)partial_call) {
-        // The type of "func" might not be exactly the same type object
-        // as "type", but if it is called using partial_call, it must have the
-        // same memory layout (fn, args and kw members).
+
+    int res = PyObject_TypeCheck(func, state->partial_type);
+    if (res == -1) {
+        return NULL;
+    }
+    if (res == 1) {
         // We can use its underlying function directly and merge the arguments.
         partialobject *part = (partialobject *)func;
         if (part->dict == NULL) {
