Modifying and saving Python text files

If you use the open() function in Python, you can read, write, and add text files What I want is to modify the existing file and save it right away.

First of all, I'll give you a quick example of what I'm curious about.

When the above txt file exists, read the file first, and then

f = open ("C:/Users/YEONGHUN/Desktop/test.txt", 'r')
file = f.read()
f.close()

I made a list of the contents of the test file, and when I found the number 7 in the for statement, I changed it to 0 and saved the test file immediately, so I wrote the code as below.

(Of course, I know that if you use the write function as an open function, it will be zero after deleting the contents of the file, but there is nothing to show you as a good example, so I wrote the idea in code.))

list = file.splitlines()

print(list)
for line in list:
    print(line)
    if line == '7':
        g = open("C:/Users/YEONGHUN/Desktop/test.txt", 'w+')
        new = g.write("0")

        g.close()

The key is if there is a basic source that can modify and save the desired part of the existing file using the for and if statements, please give us your opinions.