portia2code 0.0.14

Installation

To install portia_porter:

pip install portia2code

Purpose

The purpose of this project is to give more options to users of Portia and Scrapy.

In some cases when a spider is created with Portia it doesn’t extract the data correctly or some custom logic is needed to join different pages together. This project allows you to get around those issues by converting spiders from the JSON format used by Portia to Scrapy spiders written in Python. With the Python code it can allow users to create their own custom logic for extracting data.

For scrapy users it can give you the ability to bootstrap a spider using Portia. Rather than going to a site in your browser and manually finding the CSS/XPath selectors you can use the Portia tool to do that work for you and export the spider as python code ready to be customised.

Port your project

Once You have installed the tool you can port your project using the command:

portia_porter PROJECT_DIR OUT_DIR

You can download your portia project as python using

export PROJECT_ID="PROJECT_ID"
curl https://portia/api/projects/$PROJECT_ID/download?format=code

How it works

Spiders built with Portia consist of JSON definitions of which urls a spider should crawl and how it should extract data from the data at those urls. When running these spiders the JSON definitions are compiled into a custom Scrapy spider with trained samples used for extraction. The trained samples are used with the scrapely library to extract data from similar pages. To build one of these trained samples an annotated page must be passed to scrapely so it knows what data to extract. In older versions of Portia these annotations were found in the page by adding an attribute to each element called data-tagid=N where N is a unique incrementing integer for each open or self closing tag on the page. Newer versions of Portia have changed this and now use unique selectors for each annotated element on the page. Using these unique selectors we are able to build an extraction tree that can use item loaders on a page to extract the annotated data.

Customising Your Spiders

If you want to change the functionality you can do so as you would with any other scrapy spider. The spiders produced by Portia2Code are a custom scrapy.CrawlSpider, the code for which is included in the downloaded project.

The example below demonstrates how to make an additional API request to a metrics site when there is a meta property with the name metrics on the page.

In the example the extended spider is separated out from the original spider, this is just to demonstrate the changes that you need to make when modifying the spider. In practice you would make changes to the spider in the same class.

from scrapy.linkextractors import LinkExtractor
from scrapy.spiders import Rule

from ..utils.spiders import BasePortiaSpider
from ..utils.processors import Field
from ..utils.processors import Item
from ..items import ArticleItem


class ExampleCom(BasePortiaSpider):
    name = "www.example.com"
    start_urls = [u'http://www.example.com/search/?q=articles']
    allowed_domains = [u'www.example.com']
    rules = [
        Rule(LinkExtractor(allow=(ur'\d{6}'), deny=()), callback='parse_item',
             follow=True)
    ]
    items = [
        [Item(ArticleItem, None, u'#content', [
              Field(u'title', u'.page_title *::text', []),
              Field(u'Article', u'.article *::text', []),
              Field(u'published', u'.date *::text', []),
              Field(u'Authors', u'.authors *::text', []),
              Field(u'pdf', u'#pdf-link::attr(href)', [])])]
    ]


import json
from scrapy import Request
from six.moves.urllib.parse import urljoin


class ExtendedExampleCom(ExampleCom):
    base_api_url = 'https://api.examplemetrics.com/v1/metrics/'
    allowed_domains = [u'www.example.com', u'api.examplemetrics.com']

    def parse_item(self, response):
        for item in super(ExtendedExampleCom, self).parse_item(response):
            score = response.css('meta[name="metrics"]::attr(content)')
            if score:
                yield Request(
                    url=urljoin(self.base_api_url, score.extract()[0]),
                    callback=self.add_score, meta={'item': item})
            else:
                yield item

    def add_score(self, response):
        item = response.meta['item']
        item['score'] = json.loads(response.body)['score']
        return item

Missing Features

Some features from Portia are still not available though this porting mechanism but will hopefully be added in the future:

• Load pages using Splash depending on crawl rules

• Follow links automatically

• Text data extractors (annotations generated by highlighting text)

Future Improvements

• Only Portia 2.0 spiders are supported for now but we will be adding support for Portia 1.0 spiders.