Python实现英文文章加密传送，收到后进行解密

message = input("Enter a message:")
key = input("Enter shift number:")
secret_message=""

for lett in message:
    unicode = ord(lett)+int(key)
    if lett.isalpha():
        if lett.isupper():
            if unicode>ord(‘Z‘):
                unicode-=26
            if unicode<ord("A"):
                unicode+=26
        if lett.islower():
            if unicode > ord(‘z‘):
                unicode -= 26
            if unicode < ord("a"):
                unicode += 26
        secret_message+=chr(unicode)
    else:
        secret_message+=lett
print("加密后的字符串：",secret_message)

print("****************变成明文的步骤*************")
orig_message=""
key=-1*int(key)
for lett in secret_message:
    unicode = ord(lett) + int(key)
    if lett.isalpha():
        if lett.isupper():
            if unicode > ord(‘Z‘):
                unicode -= 26
            if unicode < ord("A"):
                unicode += 26
        if lett.islower():
            if unicode > ord(‘z‘):
                unicode -= 26
            if unicode < ord("a"):
                unicode += 26
        orig_message += chr(unicode)
    else:
        orig_message += lett
print("明文是：",orig_message)