如何在Python中写入文件中的特定行？ [英] How to write to a specific line in file in Python?

问题描述

我有一个格式的文件：

xxxxx
yyyyy
zzzzz
ttttt

我需要在xxxxx和yyyyy行之间写入文件：

And I need to write in file between xxxxx and yyyyy lines as:

xxxxx
my_line
yyyyyy
zzzzz
ttttt 

推荐答案

with open('input') as fin, open('output','w') as fout:
    for line in fin:
        fout.write(line)
        if line == 'xxxxx\n':
           next_line = next(fin)
           if next_line == 'yyyyy\n':
              fout.write('my_line\n')
           fout.write(next_line)

这将在每次出现 xxxxx \ n <之间插入您的行/ code>和文件中的 yyyyy \ n 。

另一种方法是写在看到 xxxxx \\\
yyyyy之前产生线的函数\\ n

An alternate approach would be to write a function to yield lines until it sees an xxxxx\nyyyyy\n

 def getlines(fobj,line1,line2):
     for line in iter(fobj.readline,''):  #This is necessary to get `fobj.tell` to work
         yield line
         if line == line1:
             pos = fobj.tell()
             next_line = next(fobj):
             fobj.seek(pos)
             if next_line == line2:
                 return

然后你可以使用这个直接传递给 writelines ：

Then you can use this passed directly to writelines:

with open('input') as fin, open('output','w') as fout:
    fout.writelines(getlines(fin,'xxxxx\n','yyyyy\n'))
    fout.write('my_line\n')
    fout.writelines(fin)

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