话不多说先上代码
#CasesarEncode
restxt = input()
for str in restxt:
if 'a' <= str <= 'z':
print(chr(ord('a') + (ord(str)-ord('a')+3)%26),end='')
elif 'A' <= str <= 'Z':
print(chr(ord('A') + (ord(str)-ord('A')+3)%26), end='')
else:
print('error')
测试结果: