Insert text in between file lines in python

Question

I have a file that I am currently reading from using

fo = open("file.txt", "r")

Then by doing

file = open("newfile.txt", "w")
file.write(fo.read())
file.write("Hello at the end of the file")
fo.close()
file.close()

I basically copy the file to a new one, but also add some text at the end of the newly created file. How would I be able to insert that line say, in between two lines separated by an empty line? I.e:

line 1 is right here
                        <---- I want to insert here
line 3 is right here

Can I tokenize different sentences by a delimiter like \n for new line?

Answer 1

First you should load the file using the open() method and then apply the .readlines() method, which splits on "\n" and returns a list, then you update the list of strings by inserting a new string in between the list, then simply write the contents of the list to the new file using the new_file.write("\n".join(updated_list))

NOTE: This method will only work for files which can be loaded in the memory.

with open("filename.txt", "r") as prev_file, open("new_filename.txt", "w") as new_file:
    prev_contents = prev_file.readlines()
    #Now prev_contents is a list of strings and you may add the new line to this list at any position
    prev_contents.insert(4, "\n This is a new line \n ")
    new_file.write("\n".join(prev_contents))