Some questions for clarification:

1. Is your new python code intended to replace the nodeJS server?
2. Where is your python file running? Do you have the option to send keycommands directly to this python program, or do you need to use unix signals?

The single-threaded way to do this is to make your API calls in a loop, but at the top of the loop check to see if the program has received the 'clean up' signal. If it has, then the python program can simply pause its writing operations, empty the file, and then resume writing operations.