如何同时在Python输入中追加和覆盖文件

Question

i'm trying to append and overwrite at the same time using the following code:

with open("file.txt",'r') as f:
     data=f.readlines()
     user_amount = data[2].rstrip()

def deposit(event):
    if event >= 0:
        user_amount += event
    with open("file.txt", 'a') as a:
        a.writelines(event)

def save():
    with open("file.txt",'w') as f:
         for i,line in enumerate(data,1):             
             if i == 3:                                          
                f.writelines(user_amount)
             else:
                f.writelines(line)

the file is composed by the following lines:

 first line
 second line
 user_amount
 fourth line

So, basically what I want to do is: I have a button called "Deposit" that when I press it call the function deposit() that get the values from an Entry and save in the variable user_amount. For example, if I put 10 in the Entry and press the button Deposit the user_amount sum 10 and the value is showed in a Label. So far is fine, the values are being appended to the file every time that I press the button deposit. However, there is another button called log_out that I need to press and call the function save() to save the "new amount" at the index 2! Works fine the index 2 in my file is updated to the new amount, but my problem is being that all appends are disappearing. being more clear, I need appending all values inputted by the Entry at the end of the file, and when I press the button log_out I need to save the new amount and keep all append made. The first, second and fourth line I can't modify. the output should be:

first_line
second_line
user_amount (new_amount)
fourth_line
Deposit
100.0
Deposit
50.0
Deposit
200.0... line by line ( will show all deposits made)

Answer 1

EDIT: my code probably won't work properly if event is an integer, but then the code you show wouldn't have produced the output you show, specifically you don't show anything that adds the "Deposit" line in the output you show. That's why StackOverflow asks you to show an Minimal Complete Verifiable Example https://stackoverflow.com/help/mcve when you want help with code.

The problem (I think) is that you are keeping a copy of the original file in variable data , and you aren't updating that when you call the deposit function, so when you call the save function (which rewrites the whole file) the content of variable data is written out and therefore the deposits are lost

You might be able to fix it by updating data in the deposit function like this (untested) (I am assuming event is a list):

def deposit(event):
    if event >= 0:
        user_amount += event
    with open("file.txt", 'a') as a:
        a.writelines(event)
    data.extend(event)