文本文件内容加入制定内容

import os

#add expand
src_file = raw_input("source path: ")
expand = raw_input("expand: ")

#rename
bak_src = src_file + ".bak"
os.rename(src_file, bak_src)

input = open(bak_src)
#print input
output = open(src_file, 'w')

while True:
    line = input.readline()
    if line:
# print line;
        
        line = (line.strip()) + expand
# print line
        output.write(line)
        output.write("\n")
    else:
        break
output.close()
input.close()

print "OK"