settings.rst

.. _topics-settings:

========
Settings
========

The Scrapy settings allows you to customize the behaviour of all Scrapy
components, including the core, extensions, pipelines and spiders themselves.

The infrastructure of the settings provides a global namespace of key-value mappings
that the code can use to pull configuration values from. The settings can be
populated through different mechanisms, which are described below.

The settings are also the mechanism for selecting the currently active Scrapy
project (in case you have many).

For a list of available built-in settings see: :ref:`topics-settings-ref`.

.. _topics-settings-module-envvar:

Designating the settings
========================

When you use Scrapy, you have to tell it which settings you're using. You can
do this by using an environment variable, ``SCRAPY_SETTINGS_MODULE``.

The value of ``SCRAPY_SETTINGS_MODULE`` should be in Python path syntax, e.g.
``myproject.settings``. Note that the settings module should be on the
Python `import search path`_.

.. _import search path: https://docs.python.org/2/tutorial/modules.html#the-module-search-path

Populating the settings
=======================

Settings can be populated using different mechanisms, each of which having a
different precedence. Here is the list of them in decreasing order of
precedence:

 1. Command line options (most precedence)
 2. Settings per-spider
 3. Project settings module
 4. Default settings per-command
 5. Default global settings (less precedence)

The population of these settings sources is taken care of internally, but a
manual handling is possible using API calls. See the
:ref:`topics-api-settings` topic for reference.

These mechanisms are described in more detail below.

1. Command line options
-----------------------

Arguments provided by the command line are the ones that take most precedence,
overriding any other options. You can explicitly override one (or more)
settings using the ``-s`` (or ``--set``) command line option.

.. highlight:: sh

Example::

    scrapy crawl myspider -s LOG_FILE=scrapy.log

2. Settings per-spider
----------------------

Spiders (See the :ref:`topics-spiders` chapter for reference) can define their
own settings that will take precedence and override the project ones. They can
do so by setting their :attr:`~scrapy.spiders.Spider.custom_settings` attribute::

    class MySpider(scrapy.Spider):
        name = 'myspider'

        custom_settings = {
            'SOME_SETTING': 'some value',
        }

3. Project settings module
--------------------------

The project settings module is the standard configuration file for your Scrapy
project, it's where most of your custom settings will be populated. For a
standard Scrapy project, this means you'll be adding or changing the settings
in the ``settings.py`` file created for your project.

4. Default settings per-command
-------------------------------

Each :doc:`Scrapy tool </topics/commands>` command can have its own default
settings, which override the global default settings. Those custom command
settings are specified in the ``default_settings`` attribute of the command
class.

5. Default global settings
--------------------------

The global defaults are located in the ``scrapy.settings.default_settings``
module and documented in the :ref:`topics-settings-ref` section.

How to access settings
======================

.. highlight:: python

In a spider, the settings are available through ``self.settings``::

    class MySpider(scrapy.Spider):
        name = 'myspider'
        start_urls = ['http://example.com']

        def parse(self, response):
            print("Existing settings: %s" % self.settings.attributes.keys())

.. note::
    The ``settings`` attribute is set in the base Spider class after the spider
    is initialized.  If you want to use the settings before the initialization
    (e.g., in your spider's ``__init__()`` method), you'll need to override the
    :meth:`~scrapy.spiders.Spider.from_crawler` method.

Settings can be accessed through the :attr:`scrapy.crawler.Crawler.settings`
attribute of the Crawler that is passed to ``from_crawler`` method in
extensions, middlewares and item pipelines::

    class MyExtension(object):
        def __init__(self, log_is_enabled=False):
            if log_is_enabled:
                print("log is enabled!")

        @classmethod
        def from_crawler(cls, crawler):
            settings = crawler.settings
            return cls(settings.getbool('LOG_ENABLED'))

The settings object can be used like a dict (e.g.,
``settings['LOG_ENABLED']``), but it's usually preferred to extract the setting
in the format you need it to avoid type errors, using one of the methods
provided by the :class:`~scrapy.settings.Settings` API.

Rationale for setting names
===========================

Setting names are usually prefixed with the component that they configure. For
example, proper setting names for a fictional robots.txt extension would be
``ROBOTSTXT_ENABLED``, ``ROBOTSTXT_OBEY``, ``ROBOTSTXT_CACHEDIR``, etc.


.. _topics-settings-ref:

Built-in settings reference
===========================

Here's a list of all available Scrapy settings, in alphabetical order, along
with their default values and the scope where they apply.

The scope, where available, shows where the setting is being used, if it's tied
to any particular component. In that case the module of that component will be
shown, typically an extension, middleware or pipeline. It also means that the
component must be enabled in order for the setting to have any effect.

.. setting:: AWS_ACCESS_KEY_ID

AWS_ACCESS_KEY_ID
-----------------

Default: ``None``

The AWS access key used by code that requires access to `Amazon Web services`_,
such as the :ref:`S3 feed storage backend <topics-feed-storage-s3>`.

.. setting:: AWS_SECRET_ACCESS_KEY

AWS_SECRET_ACCESS_KEY
---------------------

Default: ``None``

The AWS secret key used by code that requires access to `Amazon Web services`_,
such as the :ref:`S3 feed storage backend <topics-feed-storage-s3>`.

.. setting:: BOT_NAME

BOT_NAME
--------

Default: ``'scrapybot'``

The name of the bot implemented by this Scrapy project (also known as the
project name). This will be used to construct the User-Agent by default, and
also for logging.

It's automatically populated with your project name when you create your
project with the :command:`startproject` command.

.. setting:: CONCURRENT_ITEMS

CONCURRENT_ITEMS
----------------

Default: ``100``

Maximum number of concurrent items (per response) to process in parallel in the
Item Processor (also known as the :ref:`Item Pipeline <topics-item-pipeline>`).

.. setting:: CONCURRENT_REQUESTS

CONCURRENT_REQUESTS
-------------------

Default: ``16``

The maximum number of concurrent (ie. simultaneous) requests that will be
performed by the Scrapy downloader.

.. setting:: CONCURRENT_REQUESTS_PER_DOMAIN

CONCURRENT_REQUESTS_PER_DOMAIN
------------------------------

Default: ``8``

The maximum number of concurrent (ie. simultaneous) requests that will be
performed to any single domain.

See also: :ref:`topics-autothrottle` and its
:setting:`AUTOTHROTTLE_TARGET_CONCURRENCY` option.


.. setting:: CONCURRENT_REQUESTS_PER_IP

CONCURRENT_REQUESTS_PER_IP
--------------------------

Default: ``0``

The maximum number of concurrent (ie. simultaneous) requests that will be
performed to any single IP. If non-zero, the
:setting:`CONCURRENT_REQUESTS_PER_DOMAIN` setting is ignored, and this one is
used instead. In other words, concurrency limits will be applied per IP, not
per domain.

This setting also affects :setting:`DOWNLOAD_DELAY` and
:ref:`topics-autothrottle`: if :setting:`CONCURRENT_REQUESTS_PER_IP`
is non-zero, download delay is enforced per IP, not per domain.


.. setting:: DEFAULT_ITEM_CLASS

DEFAULT_ITEM_CLASS
------------------

Default: ``'scrapy.item.Item'``

The default class that will be used for instantiating items in the :ref:`the
Scrapy shell <topics-shell>`.

.. setting:: DEFAULT_REQUEST_HEADERS

DEFAULT_REQUEST_HEADERS
-----------------------

Default::

    {
        'Accept': 'text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8',
        'Accept-Language': 'en',
    }

The default headers used for Scrapy HTTP Requests. They're populated in the
:class:`~scrapy.downloadermiddlewares.defaultheaders.DefaultHeadersMiddleware`.

.. setting:: DEPTH_LIMIT

DEPTH_LIMIT
-----------

Default: ``0``

Scope: ``scrapy.spidermiddlewares.depth.DepthMiddleware``

The maximum depth that will be allowed to crawl for any site. If zero, no limit
will be imposed.

.. setting:: DEPTH_PRIORITY

DEPTH_PRIORITY
--------------

Default: ``0``

Scope: ``scrapy.spidermiddlewares.depth.DepthMiddleware``

An integer that is used to adjust the request priority 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)

See also: :ref:`faq-bfo-dfo` about tuning Scrapy for BFO or DFO.

.. note::

    This setting adjusts priority **in the opposite way** compared to
    other priority settings :setting:`REDIRECT_PRIORITY_ADJUST`
    and :setting:`RETRY_PRIORITY_ADJUST`.

.. setting:: DEPTH_STATS

DEPTH_STATS
-----------

Default: ``True``

Scope: ``scrapy.spidermiddlewares.depth.DepthMiddleware``

Whether to collect maximum depth stats.

.. setting:: DEPTH_STATS_VERBOSE

DEPTH_STATS_VERBOSE
-------------------

Default: ``False``

Scope: ``scrapy.spidermiddlewares.depth.DepthMiddleware``

Whether to collect verbose depth stats. If this is enabled, the number of
requests for each depth is collected in the stats.

.. setting:: DNSCACHE_ENABLED

DNSCACHE_ENABLED
----------------

Default: ``True``

Whether to enable DNS in-memory cache.

.. setting:: DNSCACHE_SIZE

DNSCACHE_SIZE
-------------

Default: ``10000``

DNS in-memory cache size.

.. setting:: DNS_TIMEOUT

DNS_TIMEOUT
-----------

Default: ``60``

Timeout for processing of DNS queries in seconds. Float is supported.

.. setting:: DOWNLOADER

DOWNLOADER
----------

Default: ``'scrapy.core.downloader.Downloader'``

The downloader to use for crawling.

.. setting:: DOWNLOADER_HTTPCLIENTFACTORY

DOWNLOADER_HTTPCLIENTFACTORY
----------------------------

Default: ``'scrapy.core.downloader.webclient.ScrapyHTTPClientFactory'``

Defines a Twisted ``protocol.ClientFactory``  class to use for HTTP/1.0
connections (for ``HTTP10DownloadHandler``).

.. note::

    HTTP/1.0 is rarely used nowadays so you can safely ignore this setting,
    unless you use Twisted<11.1, or if you really want to use HTTP/1.0
    and override :setting:`DOWNLOAD_HANDLERS_BASE` for ``http(s)`` scheme
    accordingly, i.e. to
    ``'scrapy.core.downloader.handlers.http.HTTP10DownloadHandler'``.

.. setting:: DOWNLOADER_CLIENTCONTEXTFACTORY

DOWNLOADER_CLIENTCONTEXTFACTORY
-------------------------------

Default: ``'scrapy.core.downloader.contextfactory.ScrapyClientContextFactory'``

Represents the classpath to the ContextFactory to use.

Here, "ContextFactory" is a Twisted term for SSL/TLS contexts, defining
the TLS/SSL protocol version to use, whether to do certificate verification,
or even enable client-side authentication (and various other things).

.. note::

    Scrapy default context factory **does NOT perform remote server
    certificate verification**. This is usually fine for web scraping.

    If you do need remote server certificate verification enabled,
    Scrapy also has another context factory class that you can set,
    ``'scrapy.core.downloader.contextfactory.BrowserLikeContextFactory'``,
    which uses the platform's certificates to validate remote endpoints.
    **This is only available if you use Twisted>=14.0.**

If you do use a custom ContextFactory, make sure it accepts a ``method``
parameter at init (this is the ``OpenSSL.SSL`` method mapping
:setting:`DOWNLOADER_CLIENT_TLS_METHOD`).

.. setting:: DOWNLOADER_CLIENT_TLS_METHOD

DOWNLOADER_CLIENT_TLS_METHOD
----------------------------

Default: ``'TLS'``

Use this setting to customize the TLS/SSL method used by the default
HTTP/1.1 downloader.

This setting must be one of these string values:

- ``'TLS'``: maps to OpenSSL's ``TLS_method()`` (a.k.a ``SSLv23_method()``),
  which allows protocol negotiation, starting from the highest supported
  by the platform; **default, recommended**
- ``'TLSv1.0'``: this value forces HTTPS connections to use TLS version 1.0 ;
  set this if you want the behavior of Scrapy<1.1
- ``'TLSv1.1'``: forces TLS version 1.1
- ``'TLSv1.2'``: forces TLS version 1.2
- ``'SSLv3'``: forces SSL version 3 (**not recommended**)

.. note::

    We recommend that you use PyOpenSSL>=0.13 and Twisted>=0.13
    or above (Twisted>=14.0 if you can).

.. setting:: DOWNLOADER_MIDDLEWARES

DOWNLOADER_MIDDLEWARES
----------------------

Default:: ``{}``

A dict containing the downloader middlewares enabled in your project, and their
orders. For more info see :ref:`topics-downloader-middleware-setting`.

.. setting:: DOWNLOADER_MIDDLEWARES_BASE

DOWNLOADER_MIDDLEWARES_BASE
---------------------------

Default::

    {
        'scrapy.downloadermiddlewares.robotstxt.RobotsTxtMiddleware': 100,
        'scrapy.downloadermiddlewares.httpauth.HttpAuthMiddleware': 300,
        'scrapy.downloadermiddlewares.downloadtimeout.DownloadTimeoutMiddleware': 350,
        'scrapy.downloadermiddlewares.defaultheaders.DefaultHeadersMiddleware': 400,
        'scrapy.downloadermiddlewares.useragent.UserAgentMiddleware': 500,
        'scrapy.downloadermiddlewares.retry.RetryMiddleware': 550,
        'scrapy.downloadermiddlewares.ajaxcrawl.AjaxCrawlMiddleware': 560,
        'scrapy.downloadermiddlewares.redirect.MetaRefreshMiddleware': 580,
        'scrapy.downloadermiddlewares.httpcompression.HttpCompressionMiddleware': 590,
        'scrapy.downloadermiddlewares.redirect.RedirectMiddleware': 600,
        'scrapy.downloadermiddlewares.cookies.CookiesMiddleware': 700,
        'scrapy.downloadermiddlewares.httpproxy.HttpProxyMiddleware': 750,
        'scrapy.downloadermiddlewares.chunked.ChunkedTransferMiddleware': 830,
        'scrapy.downloadermiddlewares.stats.DownloaderStats': 850,
        'scrapy.downloadermiddlewares.httpcache.HttpCacheMiddleware': 900,
    }

A dict containing the downloader middlewares enabled by default in Scrapy. Low
orders are closer to the engine, high orders are closer to the downloader. You
should never modify this setting in your project, modify
:setting:`DOWNLOADER_MIDDLEWARES` instead.  For more info see
:ref:`topics-downloader-middleware-setting`.

.. setting:: DOWNLOADER_STATS

DOWNLOADER_STATS
----------------

Default: ``True``

Whether to enable downloader stats collection.

.. setting:: DOWNLOAD_DELAY

DOWNLOAD_DELAY
--------------

Default: ``0``

The amount of time (in secs) that the downloader should wait before downloading
consecutive pages from the same website. This can be used to throttle the
crawling speed to avoid hitting servers too hard. Decimal numbers are
supported.  Example::

    DOWNLOAD_DELAY = 0.25    # 250 ms of delay

This setting is also affected by the :setting:`RANDOMIZE_DOWNLOAD_DELAY`
setting (which is enabled by default). By default, Scrapy doesn't wait a fixed
amount of time between requests, but uses a random interval between 0.5 and 1.5
* :setting:`DOWNLOAD_DELAY`.

When :setting:`CONCURRENT_REQUESTS_PER_IP` is non-zero, delays are enforced
per ip address instead of per domain.

You can also change this setting per spider by setting ``download_delay``
spider attribute.

.. setting:: DOWNLOAD_HANDLERS

DOWNLOAD_HANDLERS
-----------------

Default: ``{}``

A dict containing the request downloader handlers enabled in your project.
See :setting:`DOWNLOAD_HANDLERS_BASE` for example format.

.. setting:: DOWNLOAD_HANDLERS_BASE

DOWNLOAD_HANDLERS_BASE
----------------------

Default::

    {
        'file': 'scrapy.core.downloader.handlers.file.FileDownloadHandler',
        'http': 'scrapy.core.downloader.handlers.http.HTTPDownloadHandler',
        'https': 'scrapy.core.downloader.handlers.http.HTTPDownloadHandler',
        's3': 'scrapy.core.downloader.handlers.s3.S3DownloadHandler',
        'ftp': 'scrapy.core.downloader.handlers.ftp.FTPDownloadHandler',
    }


A dict containing the request download handlers enabled by default in Scrapy.
You should never modify this setting in your project, modify
:setting:`DOWNLOAD_HANDLERS` instead.

You can disable any of these download handlers by assigning ``None`` to their
URI scheme in :setting:`DOWNLOAD_HANDLERS`. E.g., to disable the built-in FTP
handler (without replacement), place this in your ``settings.py``::

    DOWNLOAD_HANDLERS = {
        'ftp': None,
    }

.. setting:: DOWNLOAD_TIMEOUT

DOWNLOAD_TIMEOUT
----------------

Default: ``180``

The amount of time (in secs) that the downloader will wait before timing out.

.. note::

    This timeout can be set per spider using :attr:`download_timeout`
    spider attribute and per-request using :reqmeta:`download_timeout`
    Request.meta key.

.. setting:: DOWNLOAD_MAXSIZE

DOWNLOAD_MAXSIZE
----------------

Default: `1073741824` (1024MB)

The maximum response size (in bytes) that downloader will download.

If you want to disable it set to 0.

.. reqmeta:: download_maxsize

.. note::

    This size can be set per spider using :attr:`download_maxsize`
    spider attribute and per-request using :reqmeta:`download_maxsize`
    Request.meta key.

    This feature needs Twisted >= 11.1.

.. setting:: DOWNLOAD_WARNSIZE

DOWNLOAD_WARNSIZE
-----------------

Default: `33554432` (32MB)

The response size (in bytes) that downloader will start to warn.

If you want to disable it set to 0.

.. note::

    This size can be set per spider using :attr:`download_warnsize`
    spider attribute and per-request using :reqmeta:`download_warnsize`
    Request.meta key.

    This feature needs Twisted >= 11.1.

.. setting:: DUPEFILTER_CLASS

DUPEFILTER_CLASS
----------------

Default: ``'scrapy.dupefilters.RFPDupeFilter'``

The class used to detect and filter duplicate requests.

The default (``RFPDupeFilter``) filters based on request fingerprint using
the ``scrapy.utils.request.request_fingerprint`` function. In order to change
the way duplicates are checked you could subclass ``RFPDupeFilter`` and
override its ``request_fingerprint`` method. This method should accept
scrapy :class:`~scrapy.http.Request` object and return its fingerprint
(a string).

.. setting:: DUPEFILTER_DEBUG

DUPEFILTER_DEBUG
----------------

Default: ``False``

By default, ``RFPDupeFilter`` only logs the first duplicate request.
Setting :setting:`DUPEFILTER_DEBUG` to ``True`` will make it log all duplicate requests.

.. setting:: EDITOR

EDITOR
------

Default: `depends on the environment`

The editor to use for editing spiders with the :command:`edit` command. It
defaults to the ``EDITOR`` environment variable, if set. Otherwise, it defaults
to ``vi`` (on Unix systems) or the IDLE editor (on Windows).

.. setting:: EXTENSIONS

EXTENSIONS
----------

Default:: ``{}``

A dict containing the extensions enabled in your project, and their orders.

.. setting:: EXTENSIONS_BASE

EXTENSIONS_BASE
---------------

Default::

    {
        'scrapy.extensions.corestats.CoreStats': 0,
        'scrapy.extensions.telnet.TelnetConsole': 0,
        'scrapy.extensions.memusage.MemoryUsage': 0,
        'scrapy.extensions.memdebug.MemoryDebugger': 0,
        'scrapy.extensions.closespider.CloseSpider': 0,
        'scrapy.extensions.feedexport.FeedExporter': 0,
        'scrapy.extensions.logstats.LogStats': 0,
        'scrapy.extensions.spiderstate.SpiderState': 0,
        'scrapy.extensions.throttle.AutoThrottle': 0,
    }

A dict containing the extensions available by default in Scrapy, and their
orders. This setting contains all stable built-in extensions. Keep in mind that
some of them need to be enabled through a setting.

For more information See the :ref:`extensions user guide  <topics-extensions>`
and the :ref:`list of available extensions <topics-extensions-ref>`.


.. setting:: FEED_TEMPDIR

FEED_TEMPDIR
------------

The Feed Temp dir allows you to set a custom folder to save crawler
temporary files before uploading with :ref:`FTP feed storage <topics-feed-storage-ftp>` and
:ref:`Amazon S3 <topics-feed-storage-s3>`.


.. setting:: FILES_STORE_S3_ACL

FILES_STORE_S3_ACL
------------------

Default: ``'private'``

S3-specific access control policy (ACL) for S3 files store.

.. setting:: ITEM_PIPELINES

ITEM_PIPELINES
--------------

Default: ``{}``

A dict containing the item pipelines to use, and their orders. Order values are
arbitrary, but it is customary to define them in the 0-1000 range. Lower orders
process before higher orders.

Example::

   ITEM_PIPELINES = {
       'mybot.pipelines.validate.ValidateMyItem': 300,
       'mybot.pipelines.validate.StoreMyItem': 800,
   }

.. setting:: ITEM_PIPELINES_BASE

ITEM_PIPELINES_BASE
-------------------

Default: ``{}``

A dict containing the pipelines enabled by default in Scrapy. You should never
modify this setting in your project, modify :setting:`ITEM_PIPELINES` instead.

.. setting:: LOG_ENABLED

LOG_ENABLED
-----------

Default: ``True``

Whether to enable logging.

.. setting:: LOG_ENCODING

LOG_ENCODING
------------

Default: ``'utf-8'``

The encoding to use for logging.

.. setting:: LOG_FILE

LOG_FILE
--------

Default: ``None``

File name to use for logging output. If ``None``, standard error will be used.

.. setting:: LOG_FORMAT

LOG_FORMAT
----------

Default: ``'%(asctime)s [%(name)s] %(levelname)s: %(message)s'``

String for formatting log messsages. Refer to the `Python logging documentation`_ for the whole list of available
placeholders.

.. _Python logging documentation: https://docs.python.org/2/library/logging.html#logrecord-attributes

.. setting:: LOG_DATEFORMAT

LOG_DATEFORMAT
--------------

Default: ``'%Y-%m-%d %H:%M:%S'``

String for formatting date/time, expansion of the ``%(asctime)s`` placeholder
in :setting:`LOG_FORMAT`. Refer to the `Python datetime documentation`_ for the whole list of available
directives.

.. _Python datetime documentation: https://docs.python.org/2/library/datetime.html#strftime-and-strptime-behavior

.. setting:: LOG_LEVEL

LOG_LEVEL
---------

Default: ``'DEBUG'``

Minimum level to log. Available levels are: CRITICAL, ERROR, WARNING,
INFO, DEBUG. For more info see :ref:`topics-logging`.

.. setting:: LOG_STDOUT

LOG_STDOUT
----------

Default: ``False``

If ``True``, all standard output (and error) of your process will be redirected
to the log. For example if you ``print 'hello'`` it will appear in the Scrapy
log.

.. setting:: MEMDEBUG_ENABLED

MEMDEBUG_ENABLED
----------------

Default: ``False``

Whether to enable memory debugging.

.. setting:: MEMDEBUG_NOTIFY

MEMDEBUG_NOTIFY
---------------

Default: ``[]``

When memory debugging is enabled a memory report will be sent to the specified
addresses if this setting is not empty, otherwise the report will be written to
the log.

Example::

    MEMDEBUG_NOTIFY = ['user@example.com']

.. setting:: MEMUSAGE_ENABLED

MEMUSAGE_ENABLED
----------------

Default: ``False``

Scope: ``scrapy.extensions.memusage``

Whether to enable the memory usage extension that will shutdown the Scrapy
process when it exceeds a memory limit, and also notify by email when that
happened.

See :ref:`topics-extensions-ref-memusage`.

.. setting:: MEMUSAGE_LIMIT_MB

MEMUSAGE_LIMIT_MB
-----------------

Default: ``0``

Scope: ``scrapy.extensions.memusage``

The maximum amount of memory to allow (in megabytes) before shutting down
Scrapy  (if MEMUSAGE_ENABLED is True). If zero, no check will be performed.

See :ref:`topics-extensions-ref-memusage`.

.. setting:: MEMUSAGE_CHECK_INTERVAL_SECONDS

MEMUSAGE_CHECK_INTERVAL_SECONDS
-------------------------------

.. versionadded:: 1.1

Default: ``60.0``

Scope: ``scrapy.extensions.memusage``

The :ref:`Memory usage extension <topics-extensions-ref-memusage>`
checks the current memory usage, versus the limits set by
:setting:`MEMUSAGE_LIMIT_MB` and :setting:`MEMUSAGE_WARNING_MB`,
at fixed time intervals.

This sets the length of these intervals, in seconds.

See :ref:`topics-extensions-ref-memusage`.

.. setting:: MEMUSAGE_NOTIFY_MAIL

MEMUSAGE_NOTIFY_MAIL
--------------------

Default: ``False``

Scope: ``scrapy.extensions.memusage``

A list of emails to notify if the memory limit has been reached.

Example::

    MEMUSAGE_NOTIFY_MAIL = ['user@example.com']

See :ref:`topics-extensions-ref-memusage`.

.. setting:: MEMUSAGE_REPORT

MEMUSAGE_REPORT
---------------

Default: ``False``

Scope: ``scrapy.extensions.memusage``

Whether to send a memory usage report after each spider has been closed.

See :ref:`topics-extensions-ref-memusage`.

.. setting:: MEMUSAGE_WARNING_MB

MEMUSAGE_WARNING_MB
-------------------

Default: ``0``

Scope: ``scrapy.extensions.memusage``

The maximum amount of memory to allow (in megabytes) before sending a warning
email notifying about it. If zero, no warning will be produced.

.. setting:: NEWSPIDER_MODULE

NEWSPIDER_MODULE
----------------

Default: ``''``

Module where to create new spiders using the :command:`genspider` command.

Example::

    NEWSPIDER_MODULE = 'mybot.spiders_dev'

.. setting:: RANDOMIZE_DOWNLOAD_DELAY

RANDOMIZE_DOWNLOAD_DELAY
------------------------

Default: ``True``

If enabled, Scrapy will wait a random amount of time (between 0.5 and 1.5
* :setting:`DOWNLOAD_DELAY`) while fetching requests from the same
website.

This randomization decreases the chance of the crawler being detected (and
subsequently blocked) by sites which analyze requests looking for statistically
significant similarities in the time between their requests.

The randomization policy is the same used by `wget`_ ``--random-wait`` option.

If :setting:`DOWNLOAD_DELAY` is zero (default) this option has no effect.

.. _wget: http://www.gnu.org/software/wget/manual/wget.html

.. setting:: REACTOR_THREADPOOL_MAXSIZE

REACTOR_THREADPOOL_MAXSIZE
--------------------------

Default: ``10``

The maximum limit for Twisted Reactor thread pool size. This is common
multi-purpose thread pool used by various Scrapy components. Threaded
DNS Resolver, BlockingFeedStorage, S3FilesStore just to name a few. Increase
this value if you're experiencing problems with insufficient blocking IO.

.. setting:: REDIRECT_MAX_TIMES

REDIRECT_MAX_TIMES
------------------

Default: ``20``

Defines the maximum times a request can be redirected. After this maximum the
request's response is returned as is. We used Firefox default value for the
same task.

.. setting:: REDIRECT_PRIORITY_ADJUST

REDIRECT_PRIORITY_ADJUST
------------------------

Default: ``+2``

Scope: ``scrapy.downloadermiddlewares.redirect.RedirectMiddleware``

Adjust redirect request priority relative to original request:

- **a positive priority adjust (default) means higher priority.**
- a negative priority adjust means lower priority.

.. setting:: RETRY_PRIORITY_ADJUST

RETRY_PRIORITY_ADJUST
---------------------

Default: ``-1``

Scope: ``scrapy.downloadermiddlewares.retry.RetryMiddleware``

Adjust retry request priority relative to original request:

- a positive priority adjust means higher priority.
- **a negative priority adjust (default) means lower priority.**

.. setting:: ROBOTSTXT_OBEY

ROBOTSTXT_OBEY
--------------

Default: ``False``

Scope: ``scrapy.downloadermiddlewares.robotstxt``

If enabled, Scrapy will respect robots.txt policies. For more information see
:ref:`topics-dlmw-robots`.

.. note::

    While the default value is ``False`` for historical reasons,
    this option is enabled by default in settings.py file generated
    by ``scrapy startproject`` command.

.. setting:: SCHEDULER

SCHEDULER
---------

Default: ``'scrapy.core.scheduler.Scheduler'``

The scheduler to use for crawling.

.. setting:: SCHEDULER_DEBUG

SCHEDULER_DEBUG
---------------

Default: ``False``

Setting to ``True`` will log debug information about the requests scheduler.
This currently logs(only once) if the requests cannot be serialized to disk.
Stats counter (``scheduler/unserializable``) tracks the number of times this happens.

Example entry in logs::

    1956-01-31 00:00:00+0800 [scrapy] ERROR: Unable to serialize request: <request>
    - reason: <exception> - no more unserializable requests will be logged (stats being
    collected)

.. setting:: SPIDER_CONTRACTS

SPIDER_CONTRACTS
----------------

Default:: ``{}``

A dict containing the spider contracts enabled in your project, used for
testing spiders. For more info see :ref:`topics-contracts`.

.. setting:: SPIDER_CONTRACTS_BASE

SPIDER_CONTRACTS_BASE
---------------------

Default::

    {
        'scrapy.contracts.default.UrlContract' : 1,
        'scrapy.contracts.default.ReturnsContract': 2,
        'scrapy.contracts.default.ScrapesContract': 3,
    }

A dict containing the scrapy contracts enabled by default in Scrapy. You should
never modify this setting in your project, modify :setting:`SPIDER_CONTRACTS`
instead. For more info see :ref:`topics-contracts`.

You can disable any of these contracts by assigning ``None`` to their class
path in :setting:`SPIDER_CONTRACTS`. E.g., to disable the built-in
``ScrapesContract``, place this in your ``settings.py``::

    SPIDER_CONTRACTS = {
        'scrapy.contracts.default.ScrapesContract': None,
    }

.. setting:: SPIDER_LOADER_CLASS

SPIDER_LOADER_CLASS
-------------------

Default: ``'scrapy.spiderloader.SpiderLoader'``

The class that will be used for loading spiders, which must implement the
:ref:`topics-api-spiderloader`.

.. setting:: SPIDER_MIDDLEWARES

SPIDER_MIDDLEWARES
------------------

Default:: ``{}``

A dict containing the spider middlewares enabled in your project, and their
orders. For more info see :ref:`topics-spider-middleware-setting`.

.. setting:: SPIDER_MIDDLEWARES_BASE

SPIDER_MIDDLEWARES_BASE
-----------------------

Default::

    {
        'scrapy.spidermiddlewares.httperror.HttpErrorMiddleware': 50,
        'scrapy.spidermiddlewares.offsite.OffsiteMiddleware': 500,
        'scrapy.spidermiddlewares.referer.RefererMiddleware': 700,
        'scrapy.spidermiddlewares.urllength.UrlLengthMiddleware': 800,
        'scrapy.spidermiddlewares.depth.DepthMiddleware': 900,
    }

A dict containing the spider middlewares enabled by default in Scrapy, and
their orders. Low orders are closer to the engine, high orders are closer to
the spider. For more info see :ref:`topics-spider-middleware-setting`.

.. setting:: SPIDER_MODULES

SPIDER_MODULES
--------------

Default: ``[]``

A list of modules where Scrapy will look for spiders.

Example::

    SPIDER_MODULES = ['mybot.spiders_prod', 'mybot.spiders_dev']

.. setting:: STATS_CLASS

STATS_CLASS
-----------

Default: ``'scrapy.statscollectors.MemoryStatsCollector'``

The class to use for collecting stats, who must implement the
:ref:`topics-api-stats`.

.. setting:: STATS_DUMP

STATS_DUMP
----------

Default: ``True``

Dump the :ref:`Scrapy stats <topics-stats>` (to the Scrapy log) once the spider
finishes.

For more info see: :ref:`topics-stats`.

.. setting:: STATSMAILER_RCPTS

STATSMAILER_RCPTS
-----------------

Default: ``[]`` (empty list)

Send Scrapy stats after spiders finish scraping. See
:class:`~scrapy.extensions.statsmailer.StatsMailer` for more info.

.. setting:: TELNETCONSOLE_ENABLED

TELNETCONSOLE_ENABLED
---------------------

Default: ``True``

A boolean which specifies if the :ref:`telnet console <topics-telnetconsole>`
will be enabled (provided its extension is also enabled).

.. setting:: TELNETCONSOLE_PORT

TELNETCONSOLE_PORT
------------------

Default: ``[6023, 6073]``

The port range to use for the telnet console. If set to ``None`` or ``0``, a
dynamically assigned port is used. For more info see
:ref:`topics-telnetconsole`.

.. setting:: TEMPLATES_DIR

TEMPLATES_DIR
-------------

Default: ``templates`` dir inside scrapy module

The directory where to look for templates when creating new projects with
:command:`startproject` command and new spiders with :command:`genspider`
command.

The project name must not conflict with the name of custom files or directories
in the ``project`` subdirectory.


.. setting:: URLLENGTH_LIMIT

URLLENGTH_LIMIT
---------------

Default: ``2083``

Scope: ``spidermiddlewares.urllength``

The maximum URL length to allow for crawled URLs. For more information about
the default value for this setting see: http://www.boutell.com/newfaq/misc/urllength.html

.. setting:: USER_AGENT

USER_AGENT
----------

Default: ``"Scrapy/VERSION (+http://scrapy.org)"``

The default User-Agent to use when crawling, unless overridden.


Settings documented elsewhere:
------------------------------

The following settings are documented elsewhere, please check each specific
case to see how to enable and use them.

.. settingslist::


.. _Amazon web services: https://aws.amazon.com/
.. _breadth-first order: https://en.wikipedia.org/wiki/Breadth-first_search
.. _depth-first order: https://en.wikipedia.org/wiki/Depth-first_search