The Crawler object must be instantiated with a
:class:`scrapy.Spider` subclass and a
:class:`scrapy.settings.Settings` object.

.. 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`.

.. 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.

.. 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.

.. 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.

.. 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`.

.. 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.

.. 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.

.. automethod:: crawl_async

.. automethod:: crawl

.. automethod:: stop_async

.. automethod:: stop

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,
        "addon": 15,
        "project": 20,
        "spider": 30,
        "cmdline": 40,
    }

For a detailed explanation on each settings sources, see:
:ref:`topics-settings`.

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.

.. 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

.. 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

.. method:: list()

   Get the names of the available spiders in the project.

.. 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

.. method:: get_value(key, default=None)

    Return the value for the given stats key or default if it doesn't exist.

.. method:: get_stats()

    Get all stats from the currently running spider as a dict.

.. method:: set_value(key, value)

    Set the given value for the given stats key.

.. method:: set_stats(stats)

    Override the current stats with the dict passed in ``stats`` argument.

.. 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).

.. 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.

.. 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.

.. 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:

.. method:: open_spider()

    Open the spider for stats collection.

.. method:: close_spider()

    Close the spider. After this is called, no more specific stats
    can be accessed or collected.