Re Rabbid76's answer:

Not enough rep to comment, but I tried this code and it works after the following correction:

elif tokens[0] == 'vt':
        vn_arr.append([float(c) for c in tokens[1:]])

should read

elif tokens[0] == 'vt':
        vt_arr.append([float(c) for c in tokens[1:]])

Thank you.