def increment_anon_key(key):
    """Increment the key in base-26 to the next key. The sequence looks like
    this: [a, ..., z, ba, bb, ..., bz, ..., baa, ...].

    Note that this is not the the Excel column label sequence. Base-26 is easier
    to generate and it's good enough for this use-case. Also note that this
    method performs NO validation, it assumes that all the digits are in the
    [a-z] range.
    """
    reversed_key = key[::-1]
    new_key = ''
    carry = 1
    for c in reversed_key:
        if carry == 0:
            new_key += c
            continue
        new_ord = ord(c) + carry
        if new_ord == ord('z') + 1:
            newc = 'a'
            carry = 1
        else:
            newc = chr(new_ord)
            carry = 0
        new_key += newc
    if carry == 1:
        new_key += 'b'
    return new_key[::-1]
