http://d.hatena.ne.jp/JunichiIto/20111102/1320253815

gistfile1.py

# -*- coding: utf-8 -*-
# http://d.hatena.ne.jp/JunichiIto/20111102/1320253815

A = ord('A')
N = ord('Z') - A + 1

def to_n(expr):
    return reduce(lambda n, c: n * N + ord(c) - A + 1, expr, 0)

def to_aa(n):
    s = []
    while 0 < n:
        m = (n - 1) % N
        s.append(chr(A + m))
        n = (n - 1) // N
    return ''.join(reversed(s))

def do():
    try:
        import re
        import sys
        mode = int(sys.argv[1])
        if mode == 0:
            expr = sys.argv[2].upper()
            if re.match(r'^[A-Z]+$', expr):
                print to_n(expr)
                return
        elif mode == 1:
            n = int(sys.argv[2])
            if 0 < n:
                print to_aa(n)
                return
    except:
        pass
    print 'usage: %s mode expr' % sys.argv[0]

if __name__ == '__main__':
    do()