generate strings in alphabetic order between two input strings

next_word.py

import sys


def next_word(start, current, end, diff_index):
    for i in range(len(current) - 1, diff_index - 1, -1):
        if current[i] != end[i]:
            if i < len(start) - 1:
                return current[:i] + chr(ord(current[i]) + 1) + start[i]
            else:
                return current[:i] + chr(ord(current[i]) + 1) + current[i+1:]


def get_diff_index(a, b):
    diff_index = 0
    for i in range(len(a), len(b)):
        if a[i] == b[i]:
            diff_index = i + 1
    
    return diff_index


def word_loop(start, end):
    print (start)
    result = start
    diff_index = get_diff_index(start, end)
    while result is not None:
        result = next_word(start, result, end, diff_index)
        if result:
            print (result)


def main():
    start, end = sys.argv[1:]
    if len(start) == len(end):
        if end < start:
            start, end = end, start
        word_loop(start, end)

    else:
        start, end = (start,end) if start < end else (end, start)
        word_loop('a' * len(start), start)
        word_loop(end, 'z' * len(end))

if __name__ == '__main__':
    sys.exit(main())