str = "aaaa12312"
strlist = [];
a = -1

while a<len(str)-1:
    a=a+1
    print str[a].isdigit()
    
    if str[a].isdigit():
        strlist.append('*')
    else:
        strlist.append(str[a])
    
result = ''.join(strlist)

print(result)