The function name for cmath.isinf in PyArg_ParseTuple() was wrong.

Misc/NEWS

@@ -13,6 +13,8 @@ Core and Builtins
 Library
 -------
 
+- Fixed cmath.isinf's name in its argument parsing code.
+
 - Issue #20311, #20452: poll and epoll now round the timeout away from zero,
   instead of rounding towards zero, in select and selectors modules:
   select.epoll.poll(), selectors.PollSelector.poll() and

Modules/cmathmodule.c

@@ -1060,7 +1060,7 @@ static PyObject *
 cmath_isinf(PyObject *self, PyObject *args)
 {
     Py_complex z;
-    if (!PyArg_ParseTuple(args, "D:isnan", &z))
+    if (!PyArg_ParseTuple(args, "D:isinf", &z))
         return NULL;
     return PyBool_FromLong(Py_IS_INFINITY(z.real) ||
                            Py_IS_INFINITY(z.imag));