Issue #2009: refactor varargslist and typedargslist productions to make them...

Issue #2009: refactor varargslist and typedargslist productions to make them more friendly for third-party parsers.

Grammar/Grammar

@@ -24,13 +24,13 @@ decorators: decorator+
 decorated: decorators (classdef | funcdef)
 funcdef: 'def' NAME parameters ['->' test] ':' suite
 parameters: '(' [typedargslist] ')'
-typedargslist: ((tfpdef ['=' test] ',')*
-                ('*' [tfpdef] (',' tfpdef ['=' test])* [',' '**' tfpdef] | '**' tfpdef)
-                | tfpdef ['=' test] (',' tfpdef ['=' test])* [','])
+typedargslist: (tfpdef ['=' test] (',' tfpdef ['=' test])* [','
+       ['*' [tfpdef] (',' tfpdef ['=' test])* [',' '**' tfpdef] | '**' tfpdef]]
+     |  '*' [tfpdef] (',' tfpdef ['=' test])* [',' '**' tfpdef] | '**' tfpdef)
 tfpdef: NAME [':' test]
-varargslist: ((vfpdef ['=' test] ',')*
-              ('*' [vfpdef] (',' vfpdef ['=' test])* [',' '**' vfpdef] | '**' vfpdef)
-              | vfpdef ['=' test] (',' vfpdef ['=' test])* [','])
+varargslist: (vfpdef ['=' test] (',' vfpdef ['=' test])* [','
+       ['*' [vfpdef] (',' vfpdef ['=' test])* [',' '**' vfpdef] | '**' vfpdef]]
+     |  '*' [vfpdef] (',' vfpdef ['=' test])* [',' '**' vfpdef] | '**' vfpdef)
 vfpdef: NAME
 
 stmt: simple_stmt | compound_stmt