How to in Python

[MartinRinehart at gmail.com]

I've got a pointer to a position in a line of code that contains
either a digit or a period (decimal point). I've got this comment:

            Numbers are one of these:
                integers:
                    digit+
                    0xhex_digit+
                decimals:
                    digit+.digit*[E['+'|'-']digit+]
                    .digit+[E['+'|'-']digit+]
                    digit+[.digit*]%
                    .digit+%

Common metacode: '*' = 0 or more, '+' = 1 or more, [] = optional, | =
or, ...

Now I need to instantiate the comment. How would an experienced Python
coder proceed?