在python中读取/编辑多行的方法 [英] Ways to read/edit multiple lines in python

问题描述

我想做的是从看起来像这样的文件中提取4行:

What i'm trying to do is to take 4 lines from a file that look like this:

@blablabla
blablabla #this string needs to match the amount of characters in line 4
!blablabla
blablabla #there is a string here

这种情况持续了数百次.

This goes on for a few hundred times.

我逐行阅读整个内容，更改为第四行，然后将第二行的字符数与第四行中的数量匹配.

I read the entire thing line by line, make a change to the fourth line, then want to match the second line's character count to the amount in the fourth line.

更改第四行后，我不知道如何回溯"并更改第二行.

I can't figure out how to "backtrack" and change the second line after making changes to the fourth.

with fileC as inputA:
    for line1 in inputA:
        line2 = next(inputA)
        line3 = next(inputA)
        line4 = next(inputA)

是我当前正在使用的，因为它可以让我同时处理4行，但是必须有一种更好的方法，因为在写出文件时会引起各种各样的问题.我可以用什么替代呢?

is what i'm currently using, because it lets me handle 4 lines at the same time, but there has to be a better way as causes all sorts of problems when writing away the file. What could I use as an alternative?

推荐答案

您可以这样做:

with open(filec , 'r') as f:
    lines = f.readlines() # readlines creates a list of the lines

访问第4行并对其进行操作，您将访问:

to access line 4 and do something with it you would access:

lines[3] # as lines is a list

第2行

lines[1] # etc.

然后，您可以根据需要将行写回到文件中

You could then write your lines back into a file if you wish

关于您的评论，也许是这样的:

Regarding your comment, perhaps something like this:

def change_lines(fileC):

    with open(fileC , 'r') as f:
        while True:
            lines = []
            for i in range(4):
                try:
                    lines.append(f.next()) # f.next() returns next line in file
                except StopIteration: # this will happen if you reach end of file before finding 4 more lines. 
                    #decide what you want to do here
                    return
            # otherwise this will happen
            lines[2] = lines[4] # or whatever you want to do here
            # maybe write them to a new file
            # remember you're still within the for loop here

由于您的文件平均分为四个部分，因此可以:

Since your file divides into fours evenly, this works:

def change_lines(fileC):
    with open(fileC , 'r') as f:
        while True:
            lines = []
            for i in range(4):
                try:
                    lines.append(f.next())
                except StopIteration:
                    return
            code code # do something with lines here
                      # and write to new file etc.

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