Scrapy spider middleware to ignore requests to pages containing items seen in previous crawls
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README.rst

scrapy-deltafetch

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This is a Scrapy spider middleware to ignore requests to pages containing items seen in previous crawls of the same spider, thus producing a "delta crawl" containing only new items.

This also speeds up the crawl, by reducing the number of requests that need to be crawled, and processed (typically, item requests are the most CPU intensive).

Requirements

DeltaFetch middleware depends on Python's bsddb3 package.

On Ubuntu/Debian, you may need to install libdb-dev if it's not installed already.

Installation

Install scrapy-deltafetch using pip:

$ pip install scrapy-deltafetch

Configuration

  1. Add DeltaFetch middleware by including it in SPIDER_MIDDLEWARES in your settings.py file:

    SPIDER_MIDDLEWARES = {
        'scrapy_deltafetch.DeltaFetch': 100,
    }
    

    Here, priority 100 is just an example. Set its value depending on other middlewares you may have enabled already.

  2. Enable the middleware using DELTAFETCH_ENABLED in your setting.py:

    DELTAFETCH_ENABLED = True
    

Usage

Following are the different options to control DeltaFetch middleware behavior.

Supported Scrapy settings

  • DELTAFETCH_ENABLED — to enable (or disable) this extension
  • DELTAFETCH_DIR — directory where to store state
  • DELTAFETCH_RESET — reset the state, clearing out all seen requests

These usually go in your Scrapy project's settings.py.

Supported Scrapy spider arguments

  • deltafetch_reset — same effect as DELTAFETCH_RESET setting

Example:

$ scrapy crawl example -a deltafetch_reset=1

Supported Scrapy request meta keys

  • deltafetch_key — used to define the lookup key for that request. by default it's Scrapy's default Request fingerprint function, but it can be changed to contain an item id, for example. This requires support from the spider, but makes the extension more efficient for sites that many URLs for the same item.