Understanding - Advanced, exercise 8

Text

The variable my_gr contains the string of one or more words in lowercase (e.g. "what a wonderful world"), the variable my_fn contains the string of a family name in lowercase (e.g. "doe"), and the variable my_mat the string of ten 0-9 digits (e.g. "0000123456"). Study the execution of the following functions when they are called as follows: m(my_gr, my_fn, my_mat).

def m(gr, fn, mat):
    c = ""
    gr_l = list(gr)
    fn_l = list(fn)
    if len(mat):
        idx = int(mat[0])
        gn_idx = idx % len(gr_l)
        fn_idx = idx % len(fn_l)
        n_idx = gn_idx + fn_idx
        if gr_l[gn_idx] < fn_l[fn_idx]:
            gr_l[n_idx % len(gr_l)] = fn_l[n_idx % len(fn_l)]
        else:
            fn_l[n_idx % len(fn_l)] = gr_l[n_idx % len(gr_l)]
        c = gr_l[n_idx % len(gr_l)]
        return c + m("".join(gr_l), "".join(fn_l), mat[1:])
    else:
        return c

Hints

The recursive function m processes all the digits in mat until the end. Each time such a digit is processed, a characters coming from the other two input strings is chosen and composed in the final result the function will return.

Additional material

The runnable Python file is available online. You can run it executing the command python exercise_8.py in a shell, and then following the instructions on screen to specify the intended input.