文件操作

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

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

fr.close()
fw.close()

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

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

fr.close()
fw.close()

name1 = 'jack'
name2 = 'helen'
classmates = ['jack','helen','dora','panda']
classmates.append('apple')
classmates.insert(3,'jay')
classmates.pop(4)
print(len(classmates),len(name1),classmates)