Python cookbook（数据结构与算法）保存最后N个元素的方法

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)
# Example use on a file
if __name__ == '__main__':
  with open('somefile.txt') as f:
    for line, prevlines in search(f, 'python', 5):
      for pline in prevlines:
        print(pline, end='')
      print(line, end='')
      print('-'*20)

> from collections import deque
> q=deque(maxlen=3)
> q.append(1)
> q.append(2)
> q.append(3)
> q
deque([1, 2, 3], maxlen=3)
> q.append(4)
> q
deque([2, 3, 4], maxlen=3)
> q.append(5)
> q
deque([3, 4, 5], maxlen=3)
>

> q=deque()
> q
deque([])
> q.append(1)
> q.append(2)
> q.append(3)
> q
deque([1, 2, 3])
> q.appendleft(4)
> q
deque([4, 1, 2, 3])
> q.pop()
3
> q
deque([4, 1, 2])
> q.popleft()
4
> q
deque([1, 2])
>