Python Yellow Pages Web Scraper

Im making a web scraper to take listings from Yellow Pages. The program works well, but after about 4 pages of searches, Yellow Pages does an IP check to make sure im not a robot.

Commercial web scrapers i've looked at as preliminary research work fine over 5,10 and 20 different pages - yet mine cannot.

How is this done? What do I need to do to fix mine? What is this called and how do I implement it?

Thanks in advance