python读取文件前n行

lines = []
with codecs.open("./luanxu.txt", 'r', 'gb18030') as infile:
    for i in range(25700):
        lines.append(infile.readline())
with codecs.open("./cnews.train.txt", 'w','gb18030') as f:
    for line in lines:
        f.write(line)

读取文件的前25700行数据