8.1 KiB
Core API
This section documents the Scrapy core API, and it's intended for developers of extensions and middlewares.
Crawler API
The main entry point to Scrapy API is the :class:`~scrapy.crawler.Crawler` object, passed to extensions through the from_crawler class method. This object provides access to all Scrapy core components, and it's the only way for extensions to access them and hook their functionality into Scrapy.
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.. module:: scrapy.crawler :synopsis: The Scrapy crawler
The Extension Manager is responsible for loading and keeping track of installed extensions and it's configured through the :setting:`EXTENSIONS` setting which contains a dictionary of all available extensions and their order similar to how you :ref:`configure the downloader middlewares <topics-downloader-middleware-setting>`.
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.. attribute:: request_fingerprinter
The request fingerprint builder of this crawler.
This is used from extensions and middlewares to build short, unique
identifiers for requests. See :ref:`request-fingerprints`.
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.. attribute:: settings
The settings manager of this crawler.
This is used by extensions & middlewares to access the Scrapy settings
of this crawler.
For an introduction on Scrapy settings see :ref:`topics-settings`.
For the API see :class:`~scrapy.settings.Settings` class.
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.. attribute:: signals
The signals manager of this crawler.
This is used by extensions & middlewares to hook themselves into Scrapy
functionality.
For an introduction on signals see :ref:`topics-signals`.
For the API see :class:`~scrapy.signalmanager.SignalManager` class.
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.. attribute:: stats
The stats collector of this crawler.
This is used from extensions & middlewares to record stats of their
behaviour, or access stats collected by other extensions.
For an introduction on stats collection see :ref:`topics-stats`.
For the API see :class:`~scrapy.statscollectors.StatsCollector` class.
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.. attribute:: extensions
The extension manager that keeps track of enabled extensions.
Most extensions won't need to access this attribute.
For an introduction on extensions and a list of available extensions on
Scrapy see :ref:`topics-extensions`.
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.. attribute:: engine
The execution engine, which coordinates the core crawling logic
between the scheduler, downloader and spiders.
Some extension may want to access the Scrapy engine, to inspect or
modify the downloader and scheduler behaviour, although this is an
advanced use and this API is not yet stable.
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.. attribute:: spider
Spider currently being crawled. This is an instance of the spider class
provided while constructing the crawler, and it is created after the
arguments given in the :meth:`crawl` method.
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.. method:: crawl(*args, **kwargs)
Starts the crawler by instantiating its spider class with the given
``args`` and ``kwargs`` arguments, while setting the execution engine in
motion.
Returns a deferred that is fired when the crawl is finished.
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.. automethod:: stop
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.. autoclass:: CrawlerRunner :members:
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.. autoclass:: CrawlerProcess :show-inheritance: :members: :inherited-members:
Settings API
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.. module:: scrapy.settings :synopsis: Settings manager
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.. attribute:: SETTINGS_PRIORITIES
Dictionary that sets the key name and priority level of the default
settings priorities used in Scrapy.
Each item defines a settings entry point, giving it a code name for
identification and an integer priority. Greater priorities take more
precedence over lesser ones when setting and retrieving values in the
:class:`~scrapy.settings.Settings` class.
.. code-block:: python
SETTINGS_PRIORITIES = {
"default": 0,
"command": 10,
"project": 20,
"spider": 30,
"cmdline": 40,
}
For a detailed explanation on each settings sources, see:
:ref:`topics-settings`.
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.. autofunction:: get_settings_priority
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.. autoclass:: Settings :show-inheritance: :members:
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.. autoclass:: BaseSettings :members:
SpiderLoader API
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.. module:: scrapy.spiderloader :synopsis: The spider loader
This class is in charge of retrieving and handling the spider classes defined across the project.
Custom spider loaders can be employed by specifying their path in the :setting:`SPIDER_LOADER_CLASS` project setting. They must fully implement the :class:`scrapy.interfaces.ISpiderLoader` interface to guarantee an errorless execution.
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.. method:: from_settings(settings) This class method is used by Scrapy to create an instance of the class. It's called with the current project settings, and it loads the spiders found recursively in the modules of the :setting:`SPIDER_MODULES` setting. :param settings: project settings :type settings: :class:`~scrapy.settings.Settings` instance
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.. method:: load(spider_name) Get the Spider class with the given name. It'll look into the previously loaded spiders for a spider class with name ``spider_name`` and will raise a KeyError if not found. :param spider_name: spider class name :type spider_name: str
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.. method:: list() Get the names of the available spiders in the project.
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.. method:: find_by_request(request) List the spiders' names that can handle the given request. Will try to match the request's url against the domains of the spiders. :param request: queried request :type request: :class:`~scrapy.Request` instance
Signals API
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.. automodule:: scrapy.signalmanager
:synopsis: The signal manager
:members:
:undoc-members:
Stats Collector API
There are several Stats Collectors available under the :mod:`scrapy.statscollectors` module and they all implement the Stats Collector API defined by the :class:`~scrapy.statscollectors.StatsCollector` class (which they all inherit from).
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.. module:: scrapy.statscollectors :synopsis: Stats Collectors
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.. method:: get_value(key, default=None)
Return the value for the given stats key or default if it doesn't exist.
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.. method:: get_stats()
Get all stats from the currently running spider as a dict.
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.. method:: set_value(key, value)
Set the given value for the given stats key.
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.. method:: set_stats(stats)
Override the current stats with the dict passed in ``stats`` argument.
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.. method:: inc_value(key, count=1, start=0)
Increment the value of the given stats key, by the given count,
assuming the start value given (when it's not set).
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.. method:: max_value(key, value)
Set the given value for the given key only if current value for the
same key is lower than value. If there is no current value for the
given key, the value is always set.
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.. method:: min_value(key, value)
Set the given value for the given key only if current value for the
same key is greater than value. If there is no current value for the
given key, the value is always set.
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.. method:: clear_stats()
Clear all stats.
The following methods are not part of the stats collection api but instead used when implementing custom stats collectors:
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.. method:: open_spider(spider)
Open the given spider for stats collection.
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.. method:: close_spider(spider)
Close the given spider. After this is called, no more specific stats
can be accessed or collected.