n, a name-only parameter, and d to abbreviate a default-argument parameter. a regular-expression pattern that matches legal orders of these parameter lists in a function definition.

with the ability to preface at most one name-only parameter by a * (for this problem, we will not allow ** written before a name-only parameter, although such parameters are legal in Python). All parameters are separated by commas.

The general rule you should model is: a parameter list can (a) be empty, (b) contain one n, *n, or d, (c) can contain a sequence of ns and ds with at most one *n in the sequence (front, middle, or rear).

Legal:ShouldMatch :n; d; *n; n,d,n,d; n,d,*n,d,d; ; *n,d,d,n,d; n,n,*n

Illegal:ShouldNotMatch:n,,d; nd;*n,*n;n,*nd;n,d*n,d;*n,d,d,*n