def a1_address(ri, ci):
    """Make Excel A1 style address from row/column address."""
    CHR_A = 65  # ascii code of 'A'
    ALNUM = 26  # number of alphabet
    if ci >= ALNUM:
        return chr(CHR_A + (ci // ALNUM)) + chr(CHR_A + (ci % ALNUM)) + str(ri+1)
    else:
        return chr(CHR_A + (ci % ALNUM)) + str(ri+1)