from string import ascii_lowercase


def decimal_to_alpha(index):
    """Converts an int to an alphabetical index"""
    alphanum = ''
    index += 1  # because alphabet hase no 0 and starts with 'a'
    while index:
        index -= 1  # 'a' needs to be used as next 'decimal' unit when reaching 'z':  ..., 'y', 'z', 'aa', 'ab', ...
        reste = index % 26
        index = index // 26
        alphanum = ascii_lowercase[reste] + alphanum
    return alphanum