凯撒加密与反解密（反解密要知道关键字K）

import string
def kaisa(s, k):
   lower = string.ascii_lowercase          #小写字母
   upper = string.ascii_uppercase          #大写字母
   before = string.ascii_letters
   after = lower[k:] + lower[:k] + upper[k:] + upper[:k]
   table = ''.maketrans(before, after)     #创建映射表
   return s.translate(table)

def dekaisa(s, k):
   lower = string.ascii_lowercase          #小写字母
   upper = string.ascii_uppercase          #大写字母
   before = string.ascii_letters
   after = lower[k:] + lower[:k] + upper[k:] + upper[:k]
   table = ''.maketrans(after,before )     #创建映射表       将两者互换位置
   return s.translate(table)

s = "Python is a greate programming language. I like it!"
print(s)
print(kaisa(s, 3))
print(dekaisa(kaisa(s, 3),3))