使用切片，如下所示

with open('yourfile.txt') as f:
    lines_after_17 = f.readlines()[17:]

如果文件太大量加载内存：

If the file is too big to load in memory:

with open('yourfile.txt') as f:
    for _ in xrange(17):
        next(f)
    for line in f:
        # do stuff