double_substring.py

def substrings_exist(line, size):
    max_possible_offset = len(line) - size * 2
    for offset in range(0, max_possible_offset + 1):
        border = offset + size
        substring = line[offset:border]
        the_rest_of_the_string = line[border:]
        if the_rest_of_the_string.find(substring) != -1:
            return True
    return False


def double_substring(line):
    max_possible_substring_size = len(line) // 2
    for size in range(max_possible_substring_size, 0, -1):
        if substrings_exist(line, size):
            return size
    return 0