“蚕食"最有效的方式文本文档中的第一行文本，然后将其重新保存在 python 中 [英] Most efficient way to "nibble" the first line of text from a text document then resave it in python

问题描述

我有一个文本文档，我想每隔 30 秒左右重复删除第一行文本.

I have a text document that I would like to repeatedly remove the first line of text from every 30 seconds or so.

我已经编写(或更准确地说是复制了)python 可重置计时器对象的代码，该对象允许在不要求重置或取消的情况下以非阻塞方式每 30 秒调用一次函数.

I have already written (or more accurately copied) the code for the python resettable timer object that allows a function to be called every 30 seconds in a non blocking way if not asked to reset or cancel.

python 中的可重置计时器重复直到取消

(如果有人可以检查我实现重复的方式，那没关系，因为我的 python 在运行时有时会崩溃，将不胜感激:))

(If someone could check the way I implemented the repeat in that is ok, because my python sometimes crashes while running that, would be appreciated :))

我现在想编写我的函数来加载一个文本文件，并可能复制除第一行之外的所有内容，然后将其重写为同一个文本文件.我可以这样做，我认为这样...但它是最有效的吗?

I now want to write my function to load a text file and perhaps copy all but the first line and then rewrite it to the same text file. I can do this, this way I think... but is it the most efficient ?

def removeLine():

    with open(path, 'rU') as file:
        lines = deque(file)
        try:
            print lines.popleft()
        except IndexError:
            print "Nothing to pop?"
    with open(path, 'w') as file:
        file.writelines(lines)  

这行得通，但这是最好的方法吗?

This works, but is it the best way to do it ?

推荐答案

我会使用 fileinput 模块 with inplace=True:

import fileinput

def removeLine():
    inputfile = fileinput.input(path, inplace=True, mode='rU')
    next(inputfile, None)  # skip a line *if present*
    for line in inputfile:
        print line,  # write out again, but without an extra newline
    inputfile.close()

inplace=True 导致 sys.stdout 被重定向到打开的文件，所以我们可以简单地打印"这些行.

inplace=True causes sys.stdout to be redirected to the open file, so we can simply 'print' the lines.

next() 调用用于跳过第一行；给它一个默认的 None 会抑制一个空文件的 StopIteration 异常.

The next() call is used to skip the first line; giving it a default None suppresses the StopIteration exception for an empty file.

这使得重写大文件更加高效，因为您只需要将fileinput readlines 缓冲区保留在内存中.

This makes rewriting a large file more efficient as you only need to keep the fileinput readlines buffer in memory.

我认为根本不需要 deque，即使对于您的解决方案；只需在那里使用 next() ，然后使用 list() 来捕获剩余的行:

I don't think a deque is needed at all, even for your solution; just use next() there too, then use list() to catch the remaining lines:

def removeLine():
    with open(path, 'rU') as file:
        next(file, None)  # skip a line *if present*
        lines = list(file)
    with open(path, 'w') as file:
        file.writelines(lines)  

但这需要你读取内存中的所有文件；不要对大文件这样做.

but this requires you to read all of the file in memory; don't do that with large files.

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