Running python script on webpage
I would say your best choice if you are new to web development, is to start learning Flask and the basics of "How the Web Works". There are other libraries such as Django or Cherrypy as well. Flask is a web framework that can run a server side application (a.k.a. back-end) and it's relatively simple out of the box.
However, when you say "running python script on webpage" and "build a webpage", that's not exactly how it works. You will build your webpage (a.k.a. the client-side application or the front-end) using HTML, CSS and possibly JavaScript. Web browsers can't run python.
I have a python script that takes in a .csv file and performs some data cleaning and some more advanced operations and gives back a .csv file as its output.
Is there a library I can use to build a webpage and host it on some server for users to be able to upload the input .csv file into it and be able to download the output .csv file?