def encryption(str, n): cipher = [] for i in range(len(str)): if str[i].islower(): if ord(str[i]) < 123-n: #ord('z')=122 c = chr(ord(str[i]) + n) cipher.append(c) else: c = chr(ord(str[i]) + n - 26) cipher.append(c) elif str[i].isupper(): if ord(str[i]) < 91-n: #ord('Z')=90 c = chr(ord(str[i]) + n) cipher.append(c) else: c = chr(ord(str[i]) + n - 26) cipher.append(c) else: c = str[i] cipher.append(c) cipherstr = ('').join(cipher) return cipherstr #获得用户输入的明文 plaintext = input() ciphertext = encryption(plaintext, 3) print(ciphertext)