from collections import duque
def search(lines, pattern, lens=5):
    previous_lines = deque(maxlen=lens)
    for li in lines:
        if pattern in li:
            yield li, previous_lines
        previous_lines.append(li)

if name == ‘main‘:
    with open(r’./xx.txt’) as f:
        for line, prevlines in search(f, ‘python’, 5):
            for pline in prevlines:
                print(pline, end=’’)
            print(line, end=’’)
        print(‘**’ * 20)