def default_choose_callback(files):
    """
    Default choose callback. Ask the user to determine.
    :param files: A list of duplicate file paths.
    :type files: list
    :return: A set of subscripts to remove.
    :rtype: set
    """
    print('Choose files to delete [0-%d]:' % (len(files) - 1))
    num = 0
    for file in files:
        print('%d: %s' % (num, file))
        num += 1
    s = input('Input number to delete, separated by whitespace:')
    ret = set()
    numbers = s.split(' ')
    for num in numbers:
        if not 0 <= num <= len(files) - 1:
            continue
        ret.add(int(num))
    return ret
