20.1.3. 保留最后N个元素

#!/usr/bin/env python
# -*- coding:utf8 -*-
# auther; 18793
# Date：2019/7/28 12:51
# filename: 03.保留最后 N 个元素.py

from collections import deque


def search(lines, pattern, history=5):
    previous_lines = deque(maxlen=history)
    for line in lines:
        if pattern in line:
            yield line, previous_lines
        previous_lines.append(line)


if __name__ == '__main__':
    with open(r'somefile.txt', encoding="utf8") as f:
        for line, prevlines in search(f, 'python', 5):
            for pline in prevlines:
                print(pline, end='')
            print(line, end='')
            print('-' * 20)