文件操作

fr = open('lyx.txt',mode='r',encoding='utf-8')
lyx = fr.read()
print('明文：'+lyx)
print('密文：',end='')

fw = open('penguin.txt',mode='a',encoding='utf-8')
for c in lyx:
    print(chr(ord(c)+3),end='')
    fw.write(chr(ord(c)+3))

fr.close()
fw.close()