scrapy-crawl-once

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This package provides a Scrapy_ middleware which allows to avoid re-crawling pages which were already downloaded in previous crawls.

.. _Scrapy: https://scrapy.org/

License is MIT.

Installation

::

pip install scrapy-crawl-once

Usage

To enable it, modify your settings.py::

SPIDER_MIDDLEWARES = {
    # ...
    'scrapy_crawl_once.CrawlOnceMiddleware': 100,
    # ...
}

DOWNLOADER_MIDDLEWARES = {
    # ...
    'scrapy_crawl_once.CrawlOnceMiddleware': 50,
    # ...
}

By default it does nothing. To avoid crawling a particular page multiple times set request.meta['crawl_once'] = True. When a response is received and a callback is successful, the fingerprint of such request is stored to a database. When spider schedules a new request middleware first checks if its fingerprint is in the database, and drops the request if it is there.

Other request.meta keys:

• crawl_once_value - a value to store in DB. By default, timestamp is stored.
• crawl_once_key - request unique id; by default request_fingerprint is used.

Settings

• CRAWL_ONCE_ENABLED - set it to False to disable middleware. Default is True.
• CRAWL_ONCE_PATH - a path to a folder with crawled requests database. By default .scrapy/crawl_once/ path inside a project dir is used; this folder contains <spider_name>.sqlite files with databases of seen requests.
• CRAWL_ONCE_DEFAULT - default value for crawl_once meta key (False by default). When True, all requests are handled by this middleware unless disabled explicitly using request.meta['crawl_once'] = False.

Alternatives

https://github.com/scrapy-plugins/scrapy-deltafetch is a similar package; it does almost the same. Differences:

• scrapy-deltafetch chooses whether to discard a request or not based on yielded items; scrapy-crawl-once uses an explicit request.meta['crawl_once'] flag.
• scrapy-deltafetch uses bsddb3, scrapy-crawl-once uses sqlite.

Another alternative is a built-in Scrapy HTTP cache_. Differences:

• scrapy cache stores all pages on disc, scrapy-crawl-once only keeps request fingerprints;
• scrapy cache allows a more fine grained invalidation consistent with how browsers work;
• with scrapy cache all pages are still processed (though not all pages are downloaded).

.. _Scrapy HTTP cache: https://doc.scrapy.org/en/latest/topics/downloader-middleware.html#module-scrapy.downloadermiddlewares.httpcache

Contributing

• source code: https://github.com/TeamHG-Memex/scrapy-crawl-once
• bug tracker: https://github.com/TeamHG-Memex/scrapy-crawl-once/issues

To run tests, install tox_ and run tox from the source checkout.

.. _tox: https://tox.readthedocs.io/en/latest/

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