semvec/pypi-packages huggingface dataset:
scrapy-deltafetch 2.1.0
Scrapy middleware to ignore previously crawled pages
License: BSD
Requires Python: >=3.9

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

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).

DeltaFetch middleware uses Python's dbm_ package to store requests fingerprints.

.. _dbm: https://docs.python.org/3/library/dbm.html


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 ``settings.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.

* ``deltafetch_enabled`` - if set to False it will disable deltafetch for some
  specific request