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Merge pull request #3670 from Gallaecio/depth-first-doc 

Clarify the documentation of DEPTH_PRIORITY further
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Mikhail Korobov 2019-03-14 22:10:42 +05:00 committed by GitHub
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@ -331,16 +331,16 @@ Default: ``0``
Scope: ``scrapy.spidermiddlewares.depth.DepthMiddleware``
An integer that is used to adjust the request priority based on its depth:
An integer that is used to adjust the :attr:`~scrapy.http.Request.priority` of
a :class:`~scrapy.http.Request` based on its depth.
- if zero (default), no priority adjustment is made from depth
- **a positive value will decrease the priority, i.e. higher depth
requests will be processed later** ; this is commonly used when doing
breadth-first crawls (BFO)
- a negative value will increase priority, i.e., higher depth requests
will be processed sooner (DFO)
The priority of a request is adjusted as follows::
See also: :ref:`faq-bfo-dfo` about tuning Scrapy for BFO or DFO.
request.priority = request.priority - ( depth * DEPTH_PRIORITY )
As depth increases, positive values of ``DEPTH_PRIORITY`` decrease request
priority (BFO), while negative values increase request priority (DFO). See
also :ref:`faq-bfo-dfo`.
.. note::