# abc2num.py

# abc2num.py

import string
#
def abc2num(z):
    num = z.replace('-','')
    digits = string.ascii_uppercase
    r = 0
    for exp, char in enumerate(reversed(num)):
        r = r + (pow(26, exp) * (digits.index(char) + 1))
    return r
#
def num2abc(div):
    abc=''
    while div:
        (div, mod) = divmod(div-1, 26)
        abc = chr(mod + 65) + abc
    return abc
#

abc='ABCDEFGHIJKLMNOPQRSTUVWXYZ'

print abc2num('A')      # => 1
print abc2num('Z')      # => 26
print abc2num('AA')     # => 27
print abc2num('CZ')     # => 104
print abc2num('ZZZ')    # => 18278
print abc2num('Z'*21)   # => 538857146126462423479278937046
print abc2num(abc)      # => 256094574536617744129141650397448476

print num2abc(1)                # => A
print num2abc(26)               # => Z
print num2abc(27)               # => AA
print num2abc(104)              # => CZ
print num2abc(26**3+26**2+26)   # => ZZZ