字符串轉換

import re
try:
    while True:
        n = raw_input().lower()
        l = []
        for i in n:
            if not i.isdigit():
                l.append(i);
        str = ''
        for i in xrange(len(l)):
            if l[i]=='a':
                str+='*~*'
            else:
                str+=l[i]
        print re.sub('\*\*', "", str)
except:
    pass