python文件处理，得到DNA的互补链或反向互补链

#!/usr/bin/python3
#-*-coding:utf-8 -*-
"得到DNA的互补链或者反向互补链"
f=open('./test.txt')
line=f.read()
transline=line[::-1].replace('A','t').replace('T','a').replace('G','c').replace('C','g').upper()
f.close()

fw=open('./out.txt','w')
fw.write(transline)
fw.close()