Index: Python/_warnings.c
===================================================================
--- Python/_warnings.c	(revision 88318)
+++ Python/_warnings.c	(working copy)
@@ -409,10 +409,10 @@
         else {
             PyObject *res;
 
-            if (!PyMethod_Check(show_fxn) && !PyFunction_Check(show_fxn)) {
+            if (!PyCallable_Check(show_fxn)) {
                 PyErr_SetString(PyExc_TypeError,
                                 "warnings.showwarning() must be set to a "
-                                "function or method");
+                                "callable");
                 Py_DECREF(show_fxn);
                 goto cleanup;
             }
Index: Lib/test/test_warnings.py
===================================================================
--- Lib/test/test_warnings.py	(revision 88318)
+++ Lib/test/test_warnings.py	(working copy)
@@ -519,6 +519,20 @@
             finally:
                 self.module.showwarning = old_showwarning
 
+    @support.cpython_only
+    def test_showwarning_from_c(self):
+        #Issue #10271: test we can override showarning() with a PyCFunction
+        from _testcapi import showwarning_from_c
+        with original_warnings.catch_warnings(module=self.module):
+            self.module.filterwarnings("always", category=UserWarning)
+            old_showwarning = self.module.showwarning
+            self.module.showwarning = showwarning_from_c
+            try:
+                self.assertRaisesRegex(Exception, "not an error",
+                                       self.module.warn, "test")
+            finally:
+                self.module.showwarning = old_showwarning
+
     def test_show_warning_output(self):
         # With showarning() missing, make sure that output is okay.
         text = 'test show_warning'
Index: Modules/_testcapimodule.c
===================================================================
--- Modules/_testcapimodule.c	(revision 88318)
+++ Modules/_testcapimodule.c	(working copy)
@@ -2246,6 +2246,33 @@
     return NULL;
 }
 
+/* Issue #10271: test we can override warnings.showwarning() with a PyCFunction.
+   Run via Lib/test/test_warnings.py */
+static PyObject *
+showwarning_from_c(PyObject *self, PyObject *args)
+{
+    PyObject *message, *category, *filename, *lineno;
+    PyObject *tmp;
+
+    if (!PyArg_ParseTuple(args, "O!OOO:showwarning_from_c", PyExc_Warning,
+                          &message, &category, &filename, &lineno)) {
+        return NULL;
+    }
+    tmp = PyObject_Str(message);
+    if (tmp) {
+        if (!PyUnicode_CompareWithASCIIString(tmp, "test")) {
+            PyErr_SetString(PyExc_Exception, "not an error");
+        }
+        Py_DECREF(tmp);
+    }
+    if (PyErr_Occurred()) {
+        return NULL;
+    }
+    else {
+        Py_RETURN_NONE;
+    }
+}
+
 static PyMethodDef TestMethods[] = {
     {"raise_exception",         raise_exception,                 METH_VARARGS},
     {"raise_memoryerror",   (PyCFunction)raise_memoryerror,  METH_NOARGS},
@@ -2327,6 +2354,7 @@
     {"make_exception_with_doc", (PyCFunction)make_exception_with_doc,
      METH_VARARGS | METH_KEYWORDS},
     {"crash_no_current_thread", (PyCFunction)crash_no_current_thread, METH_NOARGS},
+    {"showwarning_from_c",      (PyCFunction)showwarning_from_c, METH_VARARGS},
     {NULL, NULL} /* sentinel */
 };