在Python中找到特定行后追加 [英] Appending a specific line after having found it in Python

问题描述

我正在编写一个函数，允许用户在特定行(文件中)中查找内容，并替换该行中的部分内容，然后将其重新写入同一行中的文件中./p>

I am writing a function that allows a user to look for content in a specific line (in a file), and replace part of that content in that line, and re-writes it to the file on the same line.

def editPlayer():
    print "What information would you like to edit?"
    print "1- Forname"
    print "2- Surname"
    print "3- Email address"
    choice = int(raw_input(""))

    f = open("persons.txt","r+")
    for i in range(2): # number of type of information
        if choice == i: #check if choice equal current running of i
            line[choice-1] = str(raw_input("Enter new information: ")) #modify choice-1's element in line
            lineStr = line[0] + ";" + line[1] + ";" +  line[2] #makes list in a string

上面的代码有效，即，如果用户要编辑玩家的电子邮件地址，则他的输入将更改 line 中的第三个元素，而 lineStr 将具有所有信息，包括修改后的电子邮件地址(按相同顺序).

The above code works, i.e. if the user was to edit the player's email address, his input would change the 3rd element in line, and lineStr would have all the information including the modified email address in the same order.

我被困在需要将 lineStr 重新写入到文件中的那一行，该行与原始文件相同.该文件看起来像这样

I am stuck at the point where I need to re-write lineStr into my file on the same line as the original one. The file looks like so

Joe;Bloggs;[e-mail]
Sarah;Brown;[e-mail]

发生问题是因为在编写时

The problem occurs because when writing

f.write(lineStr)

文件的第一行将被替换，因此如果我要修改Sarah的第二名(到Stack)并将其写到文件中，该文件将类似于

the first line of the file will be replaced, so if I were to modify Sarah's second name (to Stack) and write it to the file, the file would look like

Sarah;Stack;[e-mail]
Sarah;Brown;[e-mail]

而不是外观，即:

Joe;Bloggs;[e-mail]
Sarah;Stack;[e-mail]

有人能引导我朝正确的方向前进吗?任何帮助，将不胜感激.谢谢

Could anyone lead me in the right direction? Any help would be appreciated. Thank you

推荐答案

您需要执行此操作的方法以及大多数程序执行此操作的方法-写入具有正确输出的临时文件，然后替换原始文件.这是最简单的方法.

The way you need to do this, and the way most programs do it - is to write a temporary file with the correct output, then replace the original file. This is the most fool proof way.

这是一般逻辑:

1. 打开输入文件和一个临时输出文件.
2. 从输入文件中读取一行:

1. Open the input file, and a temporary output file.
2. Read a line from the input file:

1. 如果符合替换条件，则将新修改的行写入临时输出文件；否则，将该行原样写入输出文件.

所有行处理完毕后，关闭输入文件.

删除输入文件.

使用与输入文件相同的名称重命名临时文件.

要在Python中实现它:

To implement it in Python:

import os

with open('input.txt') as i, open('output.txt', 'w') as o:
    for line in i:
       if line.startswith('Replace Me:'):
           line = 'New line, replaced the old line.\n'
       o.write(line)

os.rename('output.txt', 'input.txt')

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