arglist.txt

three possibilities:
    this: tfpdef ['=' test] (',' tfpdef ['=' test])*
          [',' [ '*' [tfpdef] (',' tfpdef ['=' test])* [',' ['**' tfpdef [',']]]
               | '**' tfpdef [',']]]

    this: dtfpdef (',' dtfpdef)*
          [',' [ '*' [tfpdef] (',' dtfpdef)* [',' ['**' tfpdef [',']]]
               | '**' tfpdef [',']]]
    a=1
    a=1, b=2, c=2
    a=1, b=2, c=2,
    a=1, b=2, c=2, *
    a=1, b=2, c=2, *, d=3
    a=1, b=2, c=2, *, d=3,
    a=1, b=2, c=2, *, d=3, e=4, **ks
    a=1, b=2, c=2, *, d=3, e=4, **ks,
    a=1, b=2, c=2, *a
    a=1, b=2, c=2, *a, d=3, e=4
    a=1, b=2, c=2, *a, d=3, e=4,
    a=1, b=2, c=2, *a, d=3, e=4, **ks
    a=1, b=2, c=2, *a, d=3, e=4, **ks,
    a=1, b=2, c=2, **ks
    a=1, b=2, c=2, **ks,

    orthis: '*' [tfpdef] (',' tfpdef ['=' test])* [',' ['**' tfpdef [',']]]

    *
    *a
    *a,b=1
    *a,b=1,c=1
    *a,b=1,c=1,
    *a,b=1,c=1,**d
    *a,b=1,c=1,**d,

    orthis: '**' tfpdef [',']

    **a
    **a,