fix compiler warning

Grammar/Grammar

@@ -24,7 +24,8 @@ decorators: decorator+
 decorated: decorators (classdef | funcdef)
 funcdef: 'def' NAME parameters ['->' test] ':' suite
 parameters: '(' [typedargslist] ')'
-typedargslist: (tfpdef ['=' test] (',' tfpdef ['=' test])* [','
+typedargslist: (tfpdef ['=' test] (',' tfpdef ['=' test])*
+               [',' '/' (',' tfpdef ['=' test])*] [','
        ['*' [tfpdef] (',' tfpdef ['=' test])* [',' '**' tfpdef] | '**' tfpdef]]
      |  '*' [tfpdef] (',' tfpdef ['=' test])* [',' '**' tfpdef] | '**' tfpdef)
 tfpdef: NAME [':' test]

Python/marshal.c

@@ -803,7 +803,7 @@ r_object(RFILE *p)
     /* NULL is a valid return value, it does not necessarily means that
        an exception is set. */
     PyObject *v, *v2;
-    Py_ssize_t idx;
+    Py_ssize_t idx = 0;
     long i, n;
     int type = r_byte(p);
     int flag;