How to write a program to track changes on a website?

Question

Parsing

Good day to all!
There is an Internet portal on which the register of organizations is located. Placement in the form of a table. Changes in the register occur as the market situation changes. Intros/exclusions, etc.
Where to google and what to study in order to write a program that would monitor changes on the site, and then be able to process this information? What is the best way to write? Are there ready-made solutions for such purposes?

Answer 1

beutifulsoup - do not use
If the server is normal - it will return the time of the last change
If there is no
requests
we take the page
we make a hash from the content, check if the page has changed we
make a database (a set of json, yaml files)
scrapy
if there are many (thousand) pages,
most of it is done by the
HTML Parser itself -lxml