scrapy-loader-upkeep 0.1a1

An alternative to the built-in ItemLoader of Scrapy which focuses on maintainability of fallback parsers.

Overview

This improves over the built-in ItemLoader of Scrapy by adding features that focuses on the maintainability of the spider over time.

This allows developers to keep track of how often parsers are being used on a crawl, allowing to safely remove obsolete css/xpath fallback rules.

Motivation

Scrapy supports adding multiple css/xpath rules in its ItemLoader by default in order to provide a convenient way for developers to keep up with site changes.

However, some sites change layouts more often than others, while some perform A/B tests for weeks/months where developers need to accommodate those changes.

These fallback css/xpath rules gets obsolete quickly and fills up the project with potentially dead code, posing a threat to the spiders’ long term maintenance.

Original idea proposal: https://github.com/scrapy/scrapy/issues/3795

Usage

from scrapy_loader_upkeep import ItemLoader

class SiteItemLoader(ItemLoader):
    pass

Using it inside a spider callback would look like:

def parse(self, response):
    loader = SiteItemLoader(response=response, stats=self.crawler.stats)

Nothing would change in the usage of this ItemLoader except for the part on injecting stat dependency to it, which is necessary to keep track of the usage of the parser rules.

Spider Example

This is taken from the examples/ directory.

$ scrapy crawl quotestoscrape_simple_has_missing

This should output in the stats:

2019-06-16 14:32:32 [scrapy.statscollectors] INFO: Dumping Scrapy stats:
{ ...
  'parser/QuotesItemLoader/author/css/1': 10,
  'parser/QuotesItemLoader/quote/css/1/missing': 10,
  'parser/QuotesItemLoader/quote/css/2': 10
  ...
}

In this example, we could see that the 1st css rule for the quote field has had instances of not being matched at all during the scrape.

Requirements

Python 3.6+