def ispoli0(string):
    for i in range(int(len(string)/2)):
        if string[i] != string[len(string)-1-i]:
            return False
    return True

def ispoli(string):

    def check(char):
        return char.lower() in '''1234567890qwertyuiopasdfghjklzxcvbnm'''

    i, j = 0, len(string) - 1

    while True:
        if i >= j:
            break
        while not check(string[i]):
            i += 1
        while not check(string[j]):
            j -= 1
        if string[i].lower() != string[j].lower():
            return False
        i += 1
        j -= 1
    return True

print(ispoli(''))
print(ispoli('a'))
print(ispoli('ab'))
print(ispoli('abc'))
print(ispoli('abcb'))
print(ispoli('abcbA'))
print(ispoli('aBCcBA'))
print(ispoli('a#$BCc&**BA'))