overwrite some data in a python file

Question

I was hoping someone could help me, I am currently trying to add some data into a text file, however the way I am doing it isnt giving me what I want. I Have a file with 20+ lines in it with text and want to overwrite the first 30 characters of the file with 30 new characters. The code I have deletes all the content and adds the 30 characters only. Please help :)

file=open("text.txt", "w")

is there something wrong with this to why its reoving all of the original data too instead of simply overwriting over it?

Answer 1

One way is to read the whole file into a single string, create a new string with first 30 characters replaced and rewrite the whole file. This can be done like this:

with open("text.txt", "r") as f:
    data = f.read()

new_thirty_characters = '<put your data here>'

new_data = new_thirty_characters + data[30:]

with open("text.txt", "w") as f:
    f.write(new_data)

Ideally, you have to check that file contains more than 30 characters after it's read. Also, do not use file and other reserved names as variable names.