# Core API

New in version 0.15.

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 `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.

The Extension Manager is responsible for loading and keeping track of installed extensions and it’s configured through the `EXTENSIONS` setting which contains a dictionary of all available extensions and their order similar to how you configure the downloader middlewares.

class `scrapy.crawler.``Crawler`(spidercls, settings)

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

  `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 Settings.

    For the API see `Settings` class.

  `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 Signals.

    For the API see `SignalManager` class.

  `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 Stats Collection.

    For the API see `StatsCollector` class.

  `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 Extensions.

  `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.

  `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 `crawl()` 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.

## Settings API

`scrapy.settings.``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 `Settings` class.

      SETTINGS_PRIORITIES = {
          'default': 0,
          'command': 10,
          'project': 20,
          'spider': 30,
          'cmdline': 40,
      }

  For a detailed explanation on each settings sources, see: Settings.

class `scrapy.settings.``Settings`(values={}, priority='project')

  This object stores Scrapy settings for the configuration of internal components, and can be used for any further customization.

  After instantiation of this class, the new object will have the global default settings described on Built-in settings reference already populated.

  Additional values can be passed on initialization with the `values` argument, and they would take the `priority` level. If the latter argument is a string, the priority name will be looked up in `SETTINGS_PRIORITIES`. Otherwise, a expecific integer should be provided.

  Once the object is created, new settings can be loaded or updated with the `set()` method, and can be accessed with the square bracket notation of dictionaries, or with the `get()` method of the instance and its value conversion variants. When requesting a stored key, the value with the highest priority will be retrieved.

  `set`(name, value, priority='project')

    Store a key/value attribute with a given priority.

    Settings should be populated before configuring the Crawler object (through the `configure()` method), otherwise they won’t have any effect.

    Parameters:

    - name (string) – the setting name
    - value (any) – the value to associate with the setting
    - priority (string or int) – the priority of the setting. Should be a key of `SETTINGS_PRIORITIES` or an integer

  `setdict`(values, priority='project')

    Store key/value pairs with a given priority.

    This is a helper function that calls `set()` for every item of `values` with the provided `priority`.

    Parameters:

    - values (dict) – the settings names and values
    - priority (string or int) – the priority of the settings. Should be a key of `SETTINGS_PRIORITIES` or an integer

  `setmodule`(module, priority='project')

    Store settings from a module with a given priority.

    This is a helper function that calls `set()` for every globally declared uppercase variable of `module` with the provided `priority`.

    Parameters:

    - module (module object or string) – the module or the path of the module
    - priority (string or int) – the priority of the settings. Should be a key of `SETTINGS_PRIORITIES` or an integer

  `get`(name, default=None)

    Get a setting value without affecting its original type.

    Parameters:

    - name (string) – the setting name
    - default (any) – the value to return if no setting is found

  `getbool`(name, default=False)

    Get a setting value as a boolean. For example, both `1` and `'1'`, and `True` return `True`, while `0`, `'0'`, `False` and `None` return `False```

    For example, settings populated through environment variables set to `'0'` will return `False` when using this method.

    Parameters:

    - name (string) – the setting name
    - default (any) – the value to return if no setting is found

  `getint`(name, default=0)

    Get a setting value as an int

    Parameters:

    - name (string) – the setting name
    - default (any) – the value to return if no setting is found

  `getfloat`(name, default=0.0)

    Get a setting value as a float

    Parameters:

    - name (string) – the setting name
    - default (any) – the value to return if no setting is found

  `getlist`(name, default=None)

    Get a setting value as a list. If the setting original type is a list, a copy of it will be returned. If it’s a string it will be split by ”,”.

    For example, settings populated through environment variables set to `'one,two'` will return a list [‘one’, ‘two’] when using this method.

    Parameters:

    - name (string) – the setting name
    - default (any) – the value to return if no setting is found

  `getdict`(name, default=None)

    Get a setting value as a dictionary. If the setting original type is a dictionary, a copy of it will be returned. If it’s a string it will evaluated as a json dictionary.

    Parameters:

    - name (string) – the setting name
    - default (any) – the value to return if no setting is found

  `copy`()

    Make a deep copy of current settings.

    This method returns a new instance of the `Settings` class, populated with the same values and their priorities.

    Modifications to the new object won’t be reflected on the original settings.

  `freeze`()

    Disable further changes to the current settings.

    After calling this method, the present state of the settings will become immutable. Trying to change values through the `set()` method and its variants won’t be possible and will be alerted.

  `frozencopy`()

    Return an immutable copy of the current settings.

    Alias for a `freeze()` call in the object returned by `copy()`

## SpiderLoader API

class `scrapy.loader.``SpiderLoader`

  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 `SPIDER_LOADER_CLASS` project setting. They must fully implement the `scrapy.interfaces.ISpiderLoader` interface to guarantee an errorless execution.

  `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 in the modules of the `SPIDER_MODULES` setting.

    Parameters: | settings (`Settings` instance) – project settings

  `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.

    Parameters: | spider_name (str) – spider class name

  `list`()

    Get the names of the available spiders in the project.

  `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.

    Parameters: | request (`Request` instance) – queried request

## Signals API

class `scrapy.signalmanager.``SignalManager`
  `connect`(receiver, signal)

    Connect a receiver function to a signal.

    The signal can be any object, although Scrapy comes with some predefined signals that are documented in the Signals section.

    Parameters:

    - receiver (callable) – the function to be connected
    - signal (object) – the signal to connect to

  `send_catch_log`(signal, **kwargs)

    Send a signal, catch exceptions and log them.

    The keyword arguments are passed to the signal handlers (connected through the `connect()` method).

  `send_catch_log_deferred`(signal, **kwargs)

    Like `send_catch_log()` but supports returning deferreds from signal handlers.

    Returns a deferred that gets fired once all signal handlers deferreds were fired. Send a signal, catch exceptions and log them.

    The keyword arguments are passed to the signal handlers (connected through the `connect()` method).

  `disconnect`(receiver, signal)

    Disconnect a receiver function from a signal. This has the opposite effect of the `connect()` method, and the arguments are the same.

  `disconnect_all`(signal)

    Disconnect all receivers from the given signal.

    Parameters: | signal (object) – the signal to disconnect from

## Stats Collector API

There are several Stats Collectors available under the `scrapy.statscollectors` module and they all implement the Stats Collector API defined by the `StatsCollector` class (which they all inherit from).

class `scrapy.statscollectors.``StatsCollector`
  `get_value`(key, default=None)

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

  `get_stats`()

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

  `set_value`(key, value)

    Set the given value for the given stats key.

  `set_stats`(stats)

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

  `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).

  `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.

  `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.

  `clear_stats`()

    Clear all stats.

  The following methods are not part of the stats collection api but instead used when implementing custom stats collectors:

  `open_spider`(spider)

    Open the given spider for stats collection.

  `close_spider`(spider)

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