6.7 KiB
Signals
Scrapy uses signals extensively to notify when certain actions occur. You can catch some of those signals in your Scrapy project or extension to perform additional tasks or extend Scrapy to add functionality not provided out of the box.
Even though signals provide several arguments, the handlers which catch them don't have to receive all of them.
For more information about working when see the documentation of pydispatcher (library used to implement signals).
Built-in signals reference
System Message: ERROR/3 (<stdin>, line 26)
Unknown directive type "module".
.. module:: scrapy.core.signals :synopsis: Signals definitions
Here's a list of signals used in Scrapy and their meaning, in alphabetical order.
engine_started
System Message: ERROR/3 (<stdin>, line 35)
Unknown directive type "signal".
.. signal:: engine_started
System Message: ERROR/3 (<stdin>, line 36)
Unknown directive type "function".
.. function:: engine_started()
Sent when the Scrapy engine is started (for example, when a crawling
process has started).
engine_stopped
System Message: ERROR/3 (<stdin>, line 44)
Unknown directive type "signal".
.. signal:: engine_stopped
System Message: ERROR/3 (<stdin>, line 45)
Unknown directive type "function".
.. function:: engine_stopped()
Sent when the Scrapy engine is stopped (for example, when a crawling
process has finished).
item_scraped
System Message: ERROR/3 (<stdin>, line 53)
Unknown directive type "signal".
.. signal:: item_scraped
System Message: ERROR/3 (<stdin>, line 54)
Unknown directive type "function".
.. function:: item_scraped(item, spider, response)
Sent when the engine receives a new scraped item from the spider, and right
before the item is sent to the :ref:`topics-item-pipeline`.
:param item: is the item scraped
:type item: :class:`~scrapy.item.Item` object
:param spider: the spider which scraped the item
:type spider: :class:`~scrapy.spider.BaseSpider` object
:param response: the response from which the item was scraped
:type response: :class:`~scrapy.http.Response` object
item_passed
System Message: ERROR/3 (<stdin>, line 71)
Unknown directive type "signal".
.. signal:: item_passed
System Message: ERROR/3 (<stdin>, line 72)
Unknown directive type "function".
.. function:: item_passed(item, spider, output)
Sent after an item has passed all the :ref:`topics-item-pipeline` stages without
being dropped.
:param item: the item which passed the pipeline
:type item: :class:`~scrapy.item.Item` object
:param spider: the spider which scraped the item
:type spider: :class:`~scrapy.spider.BaseSpider` object
:param output: the output of the item pipeline. This is typically the
same :class:`~scrapy.item.Item` object received in the ``item``
parameter, unless some pipeline stage created a new item.
item_dropped
System Message: ERROR/3 (<stdin>, line 90)
Unknown directive type "signal".
.. signal:: item_dropped
System Message: ERROR/3 (<stdin>, line 91)
Unknown directive type "function".
.. function:: item_dropped(item, spider, exception)
Sent after an item has been dropped from the :ref:`topics-item-pipeline`
when some stage raised a :exc:`~scrapy.core.exceptions.DropItem` exception.
:param item: the item dropped from the :ref:`topics-item-pipeline`
:type item: :class:`~scrapy.item.Item` object
:param spider: the spider which scraped the item
:type spider: :class:`~scrapy.spider.BaseSpider` object
:param exception: the exception (which must be a
:exc:`~scrapy.core.exceptions.DropItem` subclass) which caused the item
to be dropped
:type exception: :exc:`~scrapy.core.exceptions.DropItem` exception
spider_closed
System Message: ERROR/3 (<stdin>, line 110)
Unknown directive type "signal".
.. signal:: spider_closed
System Message: ERROR/3 (<stdin>, line 111)
Unknown directive type "function".
.. function:: spider_closed(spider, reason)
Sent after a spider has been closed. This can be used to release per-spider
resources reserved on :signal:`spider_opened`.
:param spider: the spider which has been closed
:type spider: :class:`~scrapy.spider.BaseSpider` object
:param reason: a string which describes the reason why the spider was closed. If
it was closed because the spider has completed scraping, it the reason
is ``'finished'``. Otherwise, if the spider was manually closed by
calling the ``close_spider`` engine method, then the reason is the one
passed in the ``reason`` argument of that method (which defaults to
``'cancelled'``). If the engine was shutdown (for example, by hitting
Ctrl-C to stop it) the reason will be ``'shutdown'``.
:type reason: str
spider_opened
System Message: ERROR/3 (<stdin>, line 131)
Unknown directive type "signal".
.. signal:: spider_opened
System Message: ERROR/3 (<stdin>, line 132)
Unknown directive type "function".
.. function:: spider_opened(spider)
Sent after a spider has been opened for crawling. This is typically used to
reserve per-spider resources, but can be used for any task that needs to be
performed when a spider is opened.
:param spider: the spider which has been opened
:type spider: :class:`~scrapy.spider.BaseSpider` object
spider_idle
System Message: ERROR/3 (<stdin>, line 144)
Unknown directive type "signal".
.. signal:: spider_idle
System Message: ERROR/3 (<stdin>, line 145)
Unknown directive type "function".
.. function:: spider_idle(spider)
Sent when a spider has gone idle, which means the spider has no further:
* requests waiting to be downloaded
* requests scheduled
* items being processed in the item pipeline
If the idle state persists after all handlers of this signal have finished,
the engine starts closing the spider. After the spider has finished
closing, the :signal:`spider_closed` signal is sent.
You can, for example, schedule some requests in your :signal:`spider_idle`
handler to prevent the spider from being closed.
:param spider: the spider which has gone idle
:type spider: :class:`~scrapy.spider.BaseSpider` object
request_received
System Message: ERROR/3 (<stdin>, line 166)
Unknown directive type "signal".
.. signal:: request_received
System Message: ERROR/3 (<stdin>, line 167)
Unknown directive type "function".
.. function:: request_received(request, spider)
Sent when the engine receives a :class:`~scrapy.http.Request` from a spider.
:param request: the request received
:type request: :class:`~scrapy.http.Request` object
:param spider: the spider which generated the request
:type spider: :class:`~scrapy.spider.BaseSpider` object
request_uploaded
System Message: ERROR/3 (<stdin>, line 180)
Unknown directive type "signal".
.. signal:: request_uploaded
System Message: ERROR/3 (<stdin>, line 181)
Unknown directive type "function".
.. function:: request_uploaded(request, spider)
Sent right after the download has sent a :class:`~scrapy.http.Request`.
:param request: the request uploaded/sent
:type request: :class:`~scrapy.http.Request` object
:param spider: the spider which generated the request
:type spider: :class:`~scrapy.spider.BaseSpider` object
response_received
System Message: ERROR/3 (<stdin>, line 194)
Unknown directive type "signal".
.. signal:: response_received
System Message: ERROR/3 (<stdin>, line 195)
Unknown directive type "function".
.. function:: response_received(response, spider)
:param response: the response received
:type response: :class:`~scrapy.http.Response` object
:param spider: the spider for which the response is intended
:type spider: :class:`~scrapy.spider.BaseSpider` object
Sent when the engine receives a new :class:`~scrapy.http.Response` from the
downloader.
response_downloaded
System Message: ERROR/3 (<stdin>, line 209)
Unknown directive type "signal".
.. signal:: response_downloaded
System Message: ERROR/3 (<stdin>, line 210)
Unknown directive type "function".
.. function:: response_downloaded(response, spider)
Sent by the downloader right after a ``HTTPResponse`` is downloaded.
:param response: the response downloaded
:type response: :class:`~scrapy.http.Response` object
:param spider: the spider for which the response is intended
:type spider: :class:`~scrapy.spider.BaseSpider` object