.txt file function read/write position

Question

I have this homework which I need to define a function that does the following:

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Write a function which given a text file object open in read and write mode and a string, inserts the text of the string in the file at the current read/write position. In other words, the function writes the string in the file without overwriting the rest of it. When exiting the function, the new read/write position has to be exactly at the end of the newly inserted string. The algorithm is simple; the function needs to:

1. read the content of the file starting at the current read/write position
2. write the given string at the same position step 1 started
3. write the content read at step 1. at the position where step 2. ended
4. reposition the read/write cursor at the same position step2. ended (and step 3. started).

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I'm very confused by the steps 1-4 as to what I need do to, and the professor has been no help.

here is the code that I did, but I don't think the function follows the parameter given

def readWrite(file, string):
    file.read()
    file.seek(0)
    file.write(string)
    

give_file = input("enter a file name: ")
give_string = input("enter a string: ")
try:
    readFile = open(give_file, "a+")
    file_content = readWrite(readFile, give_string)
except FileNotFoundError:
    print("File does not exist")
    exit(1)

The whole code should ask for a simple .txt file, which it would take it and a string, and add it to the original file.

example: the file is Twinkle.txt

Twinkle, twinkle, little bat!
How I wonder what you're at!
Up above the world you fly,
Like a teatray in the sky.

output:

twinkle.txt

1 Twinkle, twinkle, little bat! 
2 How I wonder what you're at! 
3 Up above the world you fly, 
4 Like a teatray in the sky.

Answer 1

I have found the way to do it and here is the function:

def readWrite(file, string):
    if not file.readable():
        print("This file is not readable")
        file.close()
        return
    if not file.writable():
        print("This file is not writable")
        file.close()
        return
    initialPosition = file.tell()
    print(initialPosition)
    readContent = file.read()
    file.seek(initialPosition)
    file.write(string)
    secondPosition = file.tell()
    print(secondPosition)
    file.write(readContent)
    file.seek(secondPosition)

basically, this takes in the file and appends to it the file name and line numbering to each row. (the code for line numbering is in the main body below).

main body:

give_file = input("enter a file name: ")
try:
    openFile = open(give_file, "r+")
    position = openFile.tell()
except FileNotFoundError:
    print(give_file, " does not exist or could not open")
    exit(1)

counter = 0
for line in openFile:
    counter += 1
openFile.seek(position)
readWrite(openFile, give_file + "\n" + "\n")

spacing = 1
while spacing <= counter:
    readWrite(openFile, str(spacing) + " ")
    openFile.readline()
    spacing += 1

openFile.close()

there might be shorter more elegant solutions out there, but this one works for me

Answer 2

I don't think I know the full answer, but I know it involves dealing with file streams. Look up the python docs for the TextIO object for that. file.write(content) in save_file deletes the existing content of the file in my experience. I believe you want to open the file in append mode at the bottom, for which the string parameter in open is 'a'

this link might help: https://www.guru99.com/reading-and-writing-files-in-python.html