Python3_Cookbook_保存有限的历史记录

#保存有限的历史记录，匹配当前行和最后检查过的N行文本
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)
        #print (previous_lines,"++++")
#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="")
                #pass
            print (line,end="")
            print ("-"*20)
############
#补充说明：
q = deque(maxlen=3)
q.append(1)##类似于list,不过只保留最新出现的3个元素###在最后面插入元素####
q.appendleft(4)###在最前插入###
q.pop()####后面弹出一个
q.popleft()####前面弹出一个