Background

In this challenge, you have to exit the python script. At that time I was asking myself, if I'm inside a python editor, how do I exit? So I pressed Ctrl+D to exit that script.

And yes! I've successfully escape that python script!

Next, since the flag is in ./flag.txt, so I was googling How to cat a file inside the python editor, and I found this:

import os

os.system("command")

Finally!! We've the flag, let's submit it.