#保留符合要求的N个条目
from collections import deque
def search(lines,pattern,history=5):
previous_lines = deque(maxlen=history)#队列
for li in lines:
if pattern in li:
yield li,previous_lines#找到pattern，并yield
previous_lines.append(li)#入队列
#Example use om s file
if __name__ == '__main__':
with open(r'/etc/passwd')as f:#被查找文件
for line,prevlines in search(f,'root',6):
for pline in prevlines:#输出队列
print(pline,end='')
print('-'*20)#括号匹配
stack = []
for c in exp:
if c in (t[0] for t in brackets):#依次找到所有左括号，并入栈
stack.append(c)
elif c in (t[1] for t in brackets):#判断右括号
if not len(stack):
print('Error')#栈空，则不匹配
break
left = stack.pop()#找到栈顶元素所匹配的右括号
bs = [t[1] for t in brackets if t[0] == left]
if bs[0] != c:#判断栈顶右括号是否与当前右括号相匹配
print('Error')
break
else:
if len(stack):#栈空，则匹配
print('Error')
else:
print('Ok')
