Web services are great. Pass them a URL. Structured data comes back. Parse it, analyse it, visualise it. Done.
Web scraping – interacting programmatically with a web page – is not so great. It requires more code and when the web page changes, the code breaks. However, in the absence of a web service, scraping is better than nothing. It can even be rather satisfying. Early in my bioinformatics career the realisation that code, rather than humans, can automate the process of submitting forms and reading the results was quite a revelation.
In this post: how to interact with a web page at the NCBI using the Mechanize library.