fix #4720: the format to PyArg_ParseTupleAndKeywords can now start with '|'

Modules/_testcapimodule.c

@@ -518,6 +518,32 @@ test_u_code(PyObject *self)
 	return Py_None;
 }
 
+static PyObject *
+test_empty_argparse(PyObject *self)
+{
+	/* Test that formats can begin with '|'. See issue #4720. */
+	PyObject *tuple, *dict = NULL;
+	static char *kwlist[] = {NULL};
+	int result;
+	tuple = PyTuple_New(0);
+	if (!tuple)
+		return NULL;
+	if ((result = PyArg_ParseTuple(tuple, "|:test_empty_argparse")) < 0)
+		goto done;
+	dict = PyDict_New();
+	if (!dict)
+		goto done;
+	result = PyArg_ParseTupleAndKeywords(tuple, dict, "|:test_empty_argparse", kwlist);
+  done:
+	Py_DECREF(tuple);
+	Py_XDECREF(dict);
+	if (result < 0)
+		return NULL;
+	else {
+		Py_RETURN_NONE;
+	}
+}
+
 static PyObject *
 codec_incrementalencoder(PyObject *self, PyObject *args)
 {
@@ -780,6 +806,7 @@ static PyMethodDef TestMethods[] = {
 	{"test_long_api",	(PyCFunction)test_long_api,	 METH_NOARGS},
 	{"test_long_numbits",	(PyCFunction)test_long_numbits,	 METH_NOARGS},
 	{"test_k_code",		(PyCFunction)test_k_code,	 METH_NOARGS},
+	{"test_empty_argparse", (PyCFunction)test_empty_argparse,METH_NOARGS},
 	{"test_null_strings",	(PyCFunction)test_null_strings,	 METH_NOARGS},
 	{"test_string_from_format", (PyCFunction)test_string_from_format, METH_NOARGS},
 	{"test_with_docstring", (PyCFunction)test_with_docstring, METH_NOARGS,

Python/getargs.c

@@ -1601,7 +1601,7 @@ vgetargskeywords(PyObject *args, PyObject *keywords, const char *format,
 		}
 	}
 
-	if (!IS_END_OF_FORMAT(*format)) {
+	if (!IS_END_OF_FORMAT(*format) && *format != '|') {
 		PyErr_Format(PyExc_RuntimeError,
 			"more argument specifiers than keyword list entries "
 			"(remaining format:'%s')", format);