For scraping the annotated fields Portia uses a library called Scrapely, which is a useful open-source tool developed independently of Portia and is available at https://github.com/scrapy/scrapely. Scrapely uses training data to build a model of what to scrape from a web page, and then this model can be applied to scrape other web pages with the same structure in future. Here is an example to show how it works:

(portia_example)$ python
>>> from scrapely import Scraper
>>> s = Scraper()
>>> train_url = 'http://example.webscraping.com/view/Afghanistan-1'
>>> s.train(train_url, {'name': 'Afghanistan', 'population': '29,121,286'})
>>> test_url = 'http://example.webscraping.com/view/United-Kingdom-239'
>>> s.scrape(test_url)
[{u'name': [u'United Kingdom'], u'population': [u'62,348,447']}]

First, Scrapely is given the data we want to scrape from the Afghanistan web page to train the model, being the country...