逐行读取文件时读取下一行和上一行

Question

使用Python，我想逐行读取一些文件，如果一行符合某些条件，我想返回上一行和下一行。什么是最好的（最pythonic）方式呢？我想做这样的事情：

with open(filename, 'r') as f:
    for line in f:
        if line.find("some string") != -1:
            print get_previous_line
            print get_next_line

---

修改

事实证明我需要阅读上一行，并且没有previous功能。问题标题和脚本相应地修改了......

Answer 1

active = False
previous = None
with open(filename, 'r') as f:
    for line in f:
        prev = previous #this is the previous line now
        previous = line 
        if active: #active contains previous line ...
           do_something_with_line_after_some_string(prev,line) #terrible function name but you get the idea
        elif line.find("some string") != -1:
           active = line
           continue
        active = False

是一个稍好的设计模式imho ...真的还有其他更多的pythonic方法来做到这一点，这取决于它实际上在做什么......