#对ASCLL码表中95个可视化字符的支持

def enChar(x,key):
    # 加密
    xid = ord(x)-first_ascll # 明文编号
    yid = (xid+key) % n # 密文编号
    y = chr(first_ascll+yid) # 求出密文字符
    return y

first_ascll = ord(' ') # 起始字符
n = 95 # 字符总数

def Caesar(text,key):
    result = ''
    for x in text:
        # 字符范围
        if ' '<=x<='~':
            x = enChar(x, key)
        result = result + x
    return result

text = 'Attack Tonight!'
key = 2
print(Caesar(text, -key))