Python在读取时截断行 [英] Python truncate lines as they are read

问题描述

我有一个应用程序读取文件中的行，并在读取每行时运行它的魔法。一旦线被读取和正确处理，我想从文件中删除行。被删除的行的备份已被保留。我想做一些类似于

$ p $ file = open（'myfile.txt'，'rw +'）
在文件中：
processLine（line）
file.truncate（line）


这似乎是一个简单的问题，但我希望做的是正确的，而不是一个复杂的seek（）和tell（）调用。

也许我所有真正想要做的是从文件中删除一个特定的行。

在这个问题上花了很长时间之后，我决定每个人都可能是对的，这不是一个好做事情的方式。这似乎是如此优雅的解决方案。我正在寻找的东西类似于一个先进先出，只是让我弹出一个文件的线。

解决方案

（$ myfile.txt'，'rw +'）作为文件：

  
 processLine（line）
 file.truncate（0）
  

单独删除每行：

  lines = open（'myfile.txt'）。readlines（）
 
为我行中的枚举（行[：]）：
 processLine（行）
 del行[i] 
 
 open（'myfile.txt '，'w'）。writelines（行）
  

只能留下导致异常的行：

  import fileinput 
 
 for fileinput.input（['myfile.txt']，inplace = 1）：
 try：processLine（line）
除外：
 sys.stdout.write（line）＃打印到'myfile.txt'
  

一般来说，正如其他人已经说过，你试图做什么是一个坏主意。

I have an application that reads lines from a file and runs its magic on each line as it is read. Once the line is read and properly processed, I would like to delete the line from the file. A backup of the removed line is already being kept. I would like to do something like

file = open('myfile.txt', 'rw+')
for line in file:
   processLine(line)
   file.truncate(line)

This seems like a simple problem, but I would like to do it right rather than a whole lot of complicated seek() and tell() calls.

Maybe all I really want to do is remove a particular line from a file.

After spending far to long on this problem I decided that everyone was probably right and this it just not a good way to do things. It just seemed so elegant solution. What I was looking for was something akin to a FIFO that would just let me pop lines out of a file.

解决方案

Remove all lines after you've done with them:

with open('myfile.txt', 'rw+') as file:
    for line in file:
        processLine(line)
    file.truncate(0)

Remove each line independently:

lines = open('myfile.txt').readlines()

for i, line in enumerate(lines[:]):
    processLine(line)
    del lines[i]

open('myfile.txt', 'w').writelines(lines)

You can leave only those lines that cause exceptions:

import fileinput

for line in fileinput.input(['myfile.txt'], inplace=1):
    try: processLine(line)
    except:
         sys.stdout.write(line) # it prints to 'myfile.txt'

In general, as other people already said it is a bad idea what you are trying to do.

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