I'm writing a web crawler which extracts cleaned news articles text and metadata using diffbot api. It also makes a logging of an article title and text changes if their source were modified since last extraction. I need some automatic way to distinguish between erased and changed article: news portals mostly don't return 404 or other error codes in case if the post was deleted, often they send 200 and page with caption like "Sorry, the article you looking for was removed". So, I need a tool or approach to detect that kind of situations, preferably it should be something written in Python or something with web API. I am totally confused and have no idea where even to begin, so any reasonable suggestions widely appreciated.
you can:

set a minimum length of an article to expect and treat any short text as a removed one
compare the Diffbot URI (a unique string) across two articles of the same URL to notice that their body has changed

These two in tandem should provide you with the diffing capability you seek.
How to distinguish between removed and modified news article during crawling web pages?