Run Python script on HTML

I have a python script that produce a figure (with matplotlib) with data from .txt files.

My goal is to run the python script from an HTML code and print the figure on a website. That way, I could just update the .txt files on the website and have a figure always up to date with the data.

I saw Flask and Django that make applications, but I already have my HTML made, so I just want a way to simply include a "run python script" somewhere in my HTML code. I saw web.py or Python CGI programming but I'm not sure if I can do what I want.

Is there another way to acheive that from a python package or should I really start a Django/Flask app? Should I have another approach?