如何在文本文件中写一行 [英] how to write a line in a text file

问题描述

嘿那里，

有点新手问题。

i知道如何读取txt文件的行。

i知道怎么写一个txt文件。


但我如何用另一个值覆盖一个行值呢？


i意思是，怎么去，比方说，行3.文本文件中的3个并替换

第3行写的东西是什么？


谢谢

<> <

解决方案

ne *** **@xit.net 写道：

嘿那里，
有点新手问题。
我知道如何阅读txt文件的行。
但是如何用另一个值覆盖一个行值？

我的意思是，怎么去，比方说，行3文本文件并替换
第3行写的是什么？

感谢
<><

你不应该尝试更新放置"除非你的文件有固定长度的行或记录。改变现有文件的长度

不能轻易进行，即使在可能的情况下也可能不会进行
。


解决此问题的经典方法是将文件作为输入读取，

处理其内容并编写新文件，最终将

替换为原始文件一个相当复杂的重命名和删除之舞。


在Python中你可以使用文本文件的readlines（）方法来构建一个列表

of all文件中的行。这样可以很容易地更改编号的

行。修改了内存中文件的内容后，您可以使用新文件的writelines（）方法创建新文件
。诀窍是

避免在发生低概率碰撞时丢失旧文件和新文件

.


自你是newbile（？）我会建议反对偏执狂 - 写下你的

代码而不用担心错误处理。你会很高兴地知道当你开始对错误处理Python感兴趣时，你会发现你需要的一切。
br $>
问候

Steve

-

Steve Holden [phone] [phone]
Holden Web LLC http://www.holdenweb.com/

食谱是

*打开你的文件阅读：f = open（''filename.txt''，'' r''）

*读取列表中的所有行：content = f.readlines（）

*关闭文件：f.close（）

*将列表中的第三个元素设置为其他内容：content [2] =

''Blahdiblah''

*重新打开文件进行写入： f = open（''filename.txt''，''w''）

*将列表写入文件：f.writelines（content）

* close文件：f.close（）

< blockquote> Gee高手，这么简单。

谢谢。从来没有想过只是在阅读时更改它然后

重写它。那会没事的。这些文件只有9行

长。

再次感谢！

Hey there,
kinda newbie question here.
i know how to read the lines of a txt file.
i know how to write a txt file.

but how do i overwrite a line value with another value ?

i mean, how do go to, say, line 3 of a text file and replace
what is written on line 3 with something else?

thanks
<><

解决方案

ne*****@xit.net wrote:

Hey there,
kinda newbie question here.
i know how to read the lines of a txt file.
i know how to write a txt file.

but how do i overwrite a line value with another value ?

i mean, how do go to, say, line 3 of a text file and replace
what is written on line 3 with something else?

thanks
<><

You shouldn''t try do "update in place" like that unless your file has
fixed-length lines or records. Altering the length of an existing file
isn''t to be lightly undertaken, and even when possible will likely not
be undertaken.

The classic way to approach this problem is to read the file as input,
processing its contents and writing a new file, which eventually
replaces the original in a fairly complex dance of renaming and deletion.

In Python you can use a text file''s readlines() method to build a list
of all the lines in a file. That makes it quite easy to change numbered
lines. Having modified the file''s content in memory you can then create
a new file using the writelines() method of a new file. The trick is to
avoid losing both the old and the new files when a low-probability crash
occurs.

Since you are newbile (?) I would advise against paranoia - write your
code without worrying about error handling. You''ll be pleased to know
that when you start to take a serious interest in error handling Python
has everything you''ll need.

regards
Steve
--
Steve Holden [phone] [phone]
Holden Web LLC http://www.holdenweb.com/

A recipe is
* open your file for reading: f = open(''filename.txt'', ''r'')
* read all lines in a list: content = f.readlines()
* close the file: f.close()
* set the third element in the list to something else: content[2] =
''Blahdiblah''
* re-open the file for writing: f = open(''filename.txt'', ''w'')
* write the list to the file: f.writelines(content)
* close the file: f.close()

Gee whiz, so easy.
thanks. Never thought about just changing it while it was read then
re-writing it. that will be just fine. these files are only 9 lines
long.
thanks again !

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