python collections duque 函数演示

duque 函数有一个 maxlen 参数，当 append 的时候，如果超过，那么最前面的就会被挤出队列

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)