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Spider Middleware
The spider middleware is a framework of hooks into Scrapy's spider processing mechanism where you can plug custom functionality to process the requests that are sent to :ref:`topics-spiders` for processing and to process the responses and item that are generated from spiders.
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Unknown interpreted text role "ref".Activating a spider middleware
To activate a spider middleware component, add it to the :setting:`SPIDER_MIDDLEWARES` setting, which is a dict whose keys are the middleware class path and their values are the middleware orders.
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Unknown interpreted text role "setting".Here's an example:
SPIDER_MIDDLEWARES = {
'myproject.middlewares.CustomSpiderMiddleware': 543,
}
The :setting:`SPIDER_MIDDLEWARES` setting is merged with the :setting:`SPIDER_MIDDLEWARES_BASE` setting defined in Scrapy (and not meant to be overridden) and then sorted by order to get the final sorted list of enabled middlewares: the first middleware is the one closer to the engine and the last is the one closer to the spider.
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Unknown interpreted text role "setting".To decide which order to assign to your middleware see the :setting:`SPIDER_MIDDLEWARES_BASE` setting and pick a value according to where you want to insert the middleware. The order does matter because each middleware performs a different action and your middleware could depend on some previous (or subsequent) middleware being applied.
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Unknown interpreted text role "setting".If you want to disable a builtin middleware (the ones defined in :setting:`SPIDER_MIDDLEWARES_BASE`, and enabled by default) you must define it in your project :setting:`SPIDER_MIDDLEWARES` setting and assign None as its value. For example, if you want to disable the off-site middleware:
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Unknown interpreted text role "setting".SPIDER_MIDDLEWARES = {
'myproject.middlewares.CustomSpiderMiddleware': 543,
'scrapy.contrib.spidermiddleware.offsite.OffsiteMiddleware': None,
}
Finally, keep in mind that some middlewares may need to be enabled through a particular setting. See each middleware documentation for more info.
Writing your own spider middleware
Writing your own spider middleware is easy. Each middleware component is a single Python class that defines one or more of the following methods:
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.. method:: process_spider_input(response, spider)
response is a :class:`~scrapy.http.Response` object spider is a :class:`~scrapy.spider.BaseSpider` object
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process_spider_input() should return either None or an iterable of :class:`~scrapy.http.Response` or :class:`~scrapy.http.Item` objects.
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Unknown interpreted text role "class".If returns None, Scrapy will continue processing this response, executing all other middlewares until, finally, the response is handled to the spider for processing.
If returns an iterable, Scrapy won't bother calling ANY other spider middleware process_spider_input() and will return the iterable back in the other direction for the process_spider_exception() and process_spider_output() methods to hook it.
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.. method:: process_spider_output(response, result, spider)
response is a :class:`~scrapy.http.Response` object result is an iterable of :class:`~scrapy.http.Request` or :class:`~scrapy.item.Item` objects spider is a :class:`~scrapy.item.BaseSpider` object
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process_spider_output() must return an iterable of :class:`~scrapy.http.Request` or :class:`~scrapy.item.Item` objects.
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.. method:: process_spider_exception(request, exception, spider)
request is a :class:`~scrapy.http.Request` object. exception is an Exception object spider is a BaseSpider object
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Unknown interpreted text role "class".Scrapy calls process_spider_exception() when a spider or process_spider_input() (from a spider middleware) raises an exception.
process_spider_exception() should return either None or an iterable of :class:`~scrapy.http.Response` or :class:`~scrapy.item.Item` objects.
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Unknown interpreted text role "class".If it returns None, Scrapy will continue processing this exception, executing any other process_spider_exception() in the middleware pipeline, until no middleware is left and the default exception handling kicks in.
If it returns an iterable the process_spider_output() pipeline kicks in, and no other process_spider_exception() will be called.
Built-in spider middleware reference
This page describes all spider middleware components that come with Scrapy. For information on how to use them and how to write your own spider middleware, see the :ref:`spider middleware usage guide <topics-spider-middleware>`.
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Unknown interpreted text role "ref".For a list of the components enabled by default (and their orders) see the :setting:`SPIDER_MIDDLEWARES_BASE` setting.
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.. module:: scrapy.contrib.spidermiddleware.depth :synopsis: Depth Spider Middleware
DepthMiddleware is a scrape middleware used for tracking the depth of each Request inside the site being scraped. It can be used to limit the maximum depth to scrape or things like that.
The :class:`DepthMiddleware` can be configured through the following settings (see the settings documentation for more info):
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:setting:`DEPTH_LIMIT` - The maximum depth that will be allowed to crawl for any site. If zero, no limit will be imposed.
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:setting:`DEPTH_STATS` - Whether to collect depth stats.
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HttpErrorMiddleware
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.. module:: scrapy.contrib.spidermiddleware.httperror :synopsis: HTTP Error Spider Middleware
Filter out unsuccessful (erroneous) HTTP responses so that spiders don't have to deal with them, which (most of the times) imposes an overhead, consumes more resources, and makes the spider logic more complex.
According to the HTTP standard, successful responses are those whose status codes are in the 200-300 range.
If you still want to process response codes outside that range, you can specify which response codes the spider is able to handle using the handle_httpstatus_list spider attribute.
For example, if you want your spider to handle 404 responses you can do this:
class MySpider(CrawlSpider): handle_httpstatus_list = [404]Keep in mind, however, that it's usually a bad idea to handle non-200 responses, unless you really know what you're doing.
For more information see: HTTP Status Code Definitions.
OffsiteMiddleware
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.. module:: scrapy.contrib.spidermiddleware.offsite :synopsis: Offiste Spider Middleware
Filters out Requests for URLs outside the domains covered by the spider.
This middleware filters out every request whose host names doesn't match :attr:`~scrapy.spider.BaseSpider.domain_name`, or the spider :attr:`~scrapy.spider.BaseSpider.domain_name` prefixed by "www.". Spider can add more domains to exclude using :attr:`~scrapy.spider.BaseSpider.extra_domain_names` attribute.
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.. module:: scrapy.contrib.spidermiddleware.requestlimit :synopsis: Request limit Spider Middleware
Limits the maximum number of requests in the scheduler for each spider. When a spider tries to schedule more than the allowed amount of requests, the new requests (returned by the spider) will be dropped.
The :class:`RequestLimitMiddleware` can be configured through the following settings (see the settings documentation for more info):
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:setting:`REQUESTS_QUEUE_SIZE` - If non zero, it will be used as an upper limit for the amount of requests that can be scheduled per domain. Can be set per spider using requests_queue_size attribute.
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RestrictMiddleware
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.. module:: scrapy.contrib.spidermiddleware.restrict :synopsis: Restrict Spider Middleware
Restricts crawling to fixed set of particular URLs.
The :class:`RestrictMiddleware` can be configured through the following settings (see the settings documentation for more info):
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:setting:`RESTRICT_TO_URLS` - Set of URLs allowed to crawl.
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UrlFilterMiddleware
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.. module:: scrapy.contrib.spidermiddleware.urlfilter :synopsis: URL Filter Spider Middleware
Canonicalizes URLs to filter out duplicated ones
UrlLengthMiddleware
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.. module:: scrapy.contrib.spidermiddleware.urllength :synopsis: URL Length Spider Middleware
Filters out requests with URLs longer than URLLENGTH_LIMIT
The :class:`UrlLengthMiddleware` can be configured through the following settings (see the settings documentation for more info):
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:setting:`URLLENGTH_LIMIT` - The maximum URL length to allow for crawled URLs.
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