Downloading a pdf from a page with a single download link or button

I would like to make a simple tool for downloading the pdf of a research paper given the url provided by the dblp database. The web pages pointed to by the urls can have different format, but the common denominator is that such a web page contains a single link or button for downloading the paper's pdf. This and this are two examples of such web pages.

How can this be achieved in python?