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# Spiders

Spiders are classes which define how a certain site (or domain) will be scraped, including how to crawl the site and how to extract scraped items from their pages. In other words, Spiders are the place where you define the custom behaviour for crawling and parsing pages for a particular site.

For spiders, the scraping cycle goes through something like this:

1. You start by generating the initial Requests to crawl the first URLs, and specify a callback function to be called with the response downloaded from those requests.

   The first requests to perform are obtained by calling the `start_requests()` method which (by default) generates `Request` for the URLs specified in the `start_urls` and the `parse` method as callback function for the Requests.

2. In the callback function, you parse the response (web page) and return either `Item` objects, `Request` objects, or an iterable of both. Those Requests will also contain a callback (maybe the same) and will then be downloaded by Scrapy and then their response handled by the specified callback.

3. In callback functions, you parse the page contents, typically using XPath Selectors (but you can also use BeautifuSoup, lxml or whatever mechanism you prefer) and generate items with the parsed data.

4. Finally, the items returned from the spider will be typically persisted in some Item pipeline.

Even though this cycle applies (more or less) to any kind of spider, there are different kinds of default spiders bundled into Scrapy for different purposes. We will talk about those types here.

## Built-in spiders reference

Scrapy comes with some useful generic spiders that you can use, to subclass your spiders from. Their aim is to provide convenient functionality for a few common scraping cases, like following all links on a site based on certain rules, crawling from Sitemaps, or parsing a XML/CSV feed.

For the examples used in the following spiders, we’ll assume you have a project with a `TestItem` declared in a `myproject.items` module:

    from scrapy.item import Item

    class TestItem(Item):
        id = Field()
        name = Field()
        description = Field()

### BaseSpider

class `scrapy.spider.``BaseSpider`

  This is the simplest spider, and the one from which every other spider must inherit from (either the ones that come bundled with Scrapy, or the ones that you write yourself). It doesn’t provide any special functionality. It just requests the given `start_urls`/`start_requests`, and calls the spider’s method `parse` for each of the resulting responses.

  `name`

    A string which defines the name for this spider. The spider name is how the spider is located (and instantiated) by Scrapy, so it must be unique. However, nothing prevents you from instantiating more than one instance of the same spider. This is the most important spider attribute and it’s required.

    Is recommended to name your spiders after the domain that their crawl.

  `allowed_domains`

    An optional list of strings containing domains that this spider is allowed to crawl. Requests for URLs not belonging to the domain names specified in this list won’t be followed if `OffsiteMiddleware` is enabled.

  `start_urls`

    A list of URLs where the spider will begin to crawl from, when no particular URLs are specified. So, the first pages downloaded will be those listed here. The subsequent URLs will be generated successively from data contained in the start URLs.

  `start_requests`()

    This method must return an iterable with the first Requests to crawl for this spider.

    This is the method called by Scrapy when the spider is opened for scraping when no particular URLs are specified. If particular URLs are specified, the `make_requests_from_url()` is used instead to create the Requests. This method is also called only once from Scrapy, so it’s safe to implement it as a generator.

    The default implementation uses `make_requests_from_url()` to generate Requests for each url in `start_urls`.

    If you want to change the Requests used to start scraping a domain, this is the method to override. For example, if you need to start by logging in using a POST request, you could do:

        def start_requests(self):
            return [FormRequest("http://www.example.com/login",
                                formdata={'user': 'john', 'pass': 'secret'},
                                callback=self.logged_in)]

        def logged_in(self, response):
            # here you would extract links to follow and return Requests for
            # each of them, with another callback
            pass

  `make_requests_from_url`(url)

    A method that receives a URL and returns a `Request` object (or a list of `Request` objects) to scrape. This method is used to construct the initial requests in the `start_requests()` method, and is typically used to convert urls to requests.

    Unless overridden, this method returns Requests with the `parse()` method as their callback function, and with dont_filter parameter enabled (see `Request` class for more info).

  `parse`(response)

    This is the default callback used by Scrapy to process downloaded responses, when their requests don’t specify a callback.

    The `parse` method is in charge of processing the response and returning scraped data and/or more URLs to follow. Other Requests callbacks have the same requirements as the `BaseSpider` class.

    This method, as well as any other Request callback, must return an iterable of `Item` objects.

    Parameters: | response – the response to parse

  `log`(message[, level, component])

    Log a message using the `scrapy.log.msg()` function, automatically populating the spider argument with the `name` of this spider. For more information see Logging.

#### BaseSpider example

Let’s see an example:

    from scrapy import log # This module is useful for printing out debug information
    from scrapy.spider import BaseSpider

    class MySpider(BaseSpider):
        name = 'example.com'
        allowed_domains = ['example.com']
        start_urls = [
            'http://www.example.com/1.html',
            'http://www.example.com/2.html',
            'http://www.example.com/3.html',
        ]

        def parse(self, response):
            self.log('A response from %s just arrived!' % response.url)

Another example returning multiples Requests and Items from a single callback:

    from scrapy.selector import HtmlXPathSelector
    from scrapy.spider import BaseSpider
    from scrapy.http import Request
    from myproject.items import MyItem

    class MySpider(BaseSpider):
        name = 'example.com'
        allowed_domains = ['example.com']
        start_urls = [
            'http://www.example.com/1.html',
            'http://www.example.com/2.html',
            'http://www.example.com/3.html',
        ]

        def parse(self, response):
            hxs = HtmlXPathSelector(response)
            for h3 in hxs.select('//h3').extract():
                yield MyItem(title=h3)

            for url in hxs.select('//a/@href').extract():
                yield Request(url, callback=self.parse)

### CrawlSpider

class `scrapy.contrib.spiders.``CrawlSpider`

  This is the most commonly used spider for crawling regular websites, as it provides a convenient mechanism for following links by defining a set of rules. It may not be the best suited for your particular web sites or project, but it’s generic enough for several cases, so you can start from it and override it as needed for more custom functionality, or just implement your own spider.

  Apart from the attributes inherited from BaseSpider (that you must specify), this class supports a new attribute:

  `rules`

    Which is a list of one (or more) `Rule` objects. Each `Rule` defines a certain behaviour for crawling the site. Rules objects are described below. If multiple rules match the same link, the first one will be used, according to the order they’re defined in this attribute.

#### Crawling rules

class `scrapy.contrib.spiders.``Rule`(link_extractor, callback=None, cb_kwargs=None, follow=None, process_links=None, process_request=None)

  `link_extractor` is a Link Extractor object which defines how links will be extracted from each crawled page.

  `callback` is a callable or a string (in which case a method from the spider object with that name will be used) to be called for each link extracted with the specified link_extractor. This callback receives a response as its first argument and must return a list containing `Item` and/or `Request` objects (or any subclass of them).

  Warning

  When writing crawl spider rules, avoid using `parse` as callback, since the `CrawlSpider` uses the `parse` method itself to implement its logic. So if you override the `parse` method, the crawl spider will no longer work.

  `cb_kwargs` is a dict containing the keyword arguments to be passed to the callback function

  `follow` is a boolean which specifies if links should be followed from each response extracted with this rule. If `callback` is None `follow` defaults to `True`, otherwise it default to `False`.

  `process_links` is a callable, or a string (in which case a method from the spider object with that name will be used) which will be called for each list of links extracted from each response using the specified `link_extractor`. This is mainly used for filtering purposes.

  > `process_request` is a callable, or a string (in which case a method from the spider object with that name will be used) which will be called with every request extracted by this rule, and must return a request or None (to filter out the request).

#### CrawlSpider example

Let’s now take a look at an example CrawlSpider with rules:

    from scrapy.contrib.spiders import CrawlSpider, Rule
    from scrapy.contrib.linkextractors.sgml import SgmlLinkExtractor
    from scrapy.selector import HtmlXPathSelector
    from scrapy.item import Item

    class MySpider(CrawlSpider):
        name = 'example.com'
        allowed_domains = ['example.com']
        start_urls = ['http://www.example.com']

        rules = (
            # Extract links matching 'category.php' (but not matching 'subsection.php')
            # and follow links from them (since no callback means follow=True by default).
            Rule(SgmlLinkExtractor(allow=('category\.php', ), deny=('subsection\.php', ))),

            # Extract links matching 'item.php' and parse them with the spider's method parse_item
            Rule(SgmlLinkExtractor(allow=('item\.php', )), callback='parse_item'),
        )

        def parse_item(self, response):
            self.log('Hi, this is an item page! %s' % response.url)

            hxs = HtmlXPathSelector(response)
            item = Item()
            item['id'] = hxs.select('//td[@id="item_id"]/text()').re(r'ID: (\d+)')
            item['name'] = hxs.select('//td[@id="item_name"]/text()').extract()
            item['description'] = hxs.select('//td[@id="item_description"]/text()').extract()
            return item

This spider would start crawling example.com’s home page, collecting category links, and item links, parsing the latter with the `parse_item` method. For each item response, some data will be extracted from the HTML using XPath, and a `Item` will be filled with it.

### XMLFeedSpider

class `scrapy.contrib.spiders.``XMLFeedSpider`

  XMLFeedSpider is designed for parsing XML feeds by iterating through them by a certain node name. The iterator can be chosen from: `iternodes`, `xml`, and `html`. It’s recommended to use the `iternodes` iterator for performance reasons, since the `xml` and `html` iterators generate the whole DOM at once in order to parse it. However, using `html` as the iterator may be useful when parsing XML with bad markup.

  To set the iterator and the tag name, you must define the following class attributes:

  `iterator`

    A string which defines the iterator to use. It can be either:

    > - `'iternodes'` - a fast iterator based on regular expressions
    > - `'html'` - an iterator which uses HtmlXPathSelector. Keep in mind this uses DOM parsing and must load all DOM in memory which could be a problem for big feeds
    > - `'xml'` - an iterator which uses XmlXPathSelector. Keep in mind this uses DOM parsing and must load all DOM in memory which could be a problem for big feeds

    It defaults to: `'iternodes'`.

  `itertag`

    A string with the name of the node (or element) to iterate in. Example:

        itertag = 'product'

  `namespaces`

    A list of `(prefix, uri)` tuples which define the namespaces available in that document that will be processed with this spider. The `prefix` and `uri` will be used to automatically register namespaces using the `register_namespace()` method.

    You can then specify nodes with namespaces in the `itertag` attribute.

    Example:

        class YourSpider(XMLFeedSpider):

            namespaces = [('n', 'http://www.sitemaps.org/schemas/sitemap/0.9')]
            itertag = 'n:url'
            # ...

  Apart from these new attributes, this spider has the following overrideable methods too:

  `adapt_response`(response)

    A method that receives the response as soon as it arrives from the spider middleware, before the spider starts parsing it. It can be used to modify the response body before parsing it. This method receives a response and also returns a response (it could be the same or another one).

  `parse_node`(response, selector)

    This method is called for the nodes matching the provided tag name (`itertag`). Receives the response and an XPathSelector for each node. Overriding this method is mandatory. Otherwise, you spider won’t work. This method must return either a `Item` object, a `Request` object, or an iterable containing any of them.

  `process_results`(response, results)

    This method is called for each result (item or request) returned by the spider, and it’s intended to perform any last time processing required before returning the results to the framework core, for example setting the item IDs. It receives a list of results and the response which originated those results. It must return a list of results (Items or Requests).

#### XMLFeedSpider example

These spiders are pretty easy to use, let’s have a look at one example:

    from scrapy import log
    from scrapy.contrib.spiders import XMLFeedSpider
    from myproject.items import TestItem

    class MySpider(XMLFeedSpider):
        name = 'example.com'
        allowed_domains = ['example.com']
        start_urls = ['http://www.example.com/feed.xml']
        iterator = 'iternodes' # This is actually unnecesary, since it's the default value
        itertag = 'item'

        def parse_node(self, response, node):
            log.msg('Hi, this is a <%s> node!: %s' % (self.itertag, ''.join(node.extract())))

            item = Item()
            item['id'] = node.select('@id').extract()
            item['name'] = node.select('name').extract()
            item['description'] = node.select('description').extract()
            return item

Basically what we did up there was to create a spider that downloads a feed from the given `start_urls`, and then iterates through each of its `item` tags, prints them out, and stores some random data in an `Item`.

### CSVFeedSpider

class `scrapy.contrib.spiders.``CSVFeedSpider`

  This spider is very similar to the XMLFeedSpider, except that it iterates over rows, instead of nodes. The method that gets called in each iteration is `parse_row()`.

  `delimiter`

    A string with the separator character for each field in the CSV file Defaults to `','` (comma).

  `headers`

    A list of the rows contained in the file CSV feed which will be used to extract fields from it.

  `parse_row`(response, row)

    Receives a response and a dict (representing each row) with a key for each provided (or detected) header of the CSV file. This spider also gives the opportunity to override `adapt_response` and `process_results` methods for pre- and post-processing purposes.

#### CSVFeedSpider example

Let’s see an example similar to the previous one, but using a `CSVFeedSpider`:

    from scrapy import log
    from scrapy.contrib.spiders import CSVFeedSpider
    from myproject.items import TestItem

    class MySpider(CSVFeedSpider):
        name = 'example.com'
        allowed_domains = ['example.com']
        start_urls = ['http://www.example.com/feed.csv']
        delimiter = ';'
        headers = ['id', 'name', 'description']

        def parse_row(self, response, row):
            log.msg('Hi, this is a row!: %r' % row)

            item = TestItem()
            item['id'] = row['id']
            item['name'] = row['name']
            item['description'] = row['description']
            return item

### SitemapSpider

class `scrapy.contrib.spiders.``SitemapSpider`

  SitemapSpider allows you to crawl a site by discovering the URLs using Sitemaps.

  It supports nested sitemaps and discovering sitemap urls from robots.txt.

  `sitemap_urls`

    A list of urls pointing to the sitemaps whose urls you want to crawl.

    You can also point to a robots.txt and it will be parsed to extract sitemap urls from it.

  `sitemap_rules`

    A list of tuples `(regex, callback)` where:

    - `regex` is a regular expression to match urls extracted from sitemaps. `regex` can be either a str or a compiled regex object.
    - callback is the callback to use for processing the urls that match the regular expression. `callback` can be a string (indicating the name of a spider method) or a callable.

    For example:

        sitemap_rules = [('/product/', 'parse_product')]

    Rules are applied in order, and only the first one that matches will be used.

    If you omit this attribute, all urls found in sitemaps will be processed with the `parse` callback.

  `sitemap_follow`

    A list of regexes of sitemap that should be followed. This is is only for sites that use Sitemap index files that point to other sitemap files.

    By default, all sitemaps are followed.

#### SitemapSpider examples

Simplest example: process all urls discovered through sitemaps using the `parse` callback:

    from scrapy.contrib.spiders import SitemapSpider

    class MySpider(SitemapSpider):
        sitemap_urls = ['http://www.example.com/sitemap.xml']

        def parse(self, response):
            pass # ... scrape item here ...

Process some urls with certain callback and other urls with a different callback:

    from scrapy.contrib.spiders import SitemapSpider

    class MySpider(SitemapSpider):
        sitemap_urls = ['http://www.example.com/sitemap.xml']
        sitemap_rules = [
            ('/product/', 'parse_product'),
            ('/category/', 'parse_category'),
        ]

        def parse_product(self, response):
            pass # ... scrape product ...

        def parse_category(self, response):
            pass # ... scrape category ...

Follow sitemaps defined in the robots.txt file and only follow sitemaps whose url contains `/sitemap_shop`:

    from scrapy.contrib.spiders import SitemapSpider

    class MySpider(SitemapSpider):
        sitemap_urls = ['http://www.example.com/robots.txt']
        sitemap_rules = [
            ('/shop/', 'parse_shop'),
        ]
        sitemap_follow = ['/sitemap_shops']

        def parse_shop(self, response):
            pass # ... scrape shop here ...

Combine SitemapSpider with other sources of urls:

    from scrapy.contrib.spiders import SitemapSpider

    class MySpider(SitemapSpider):
        sitemap_urls = ['http://www.example.com/robots.txt']
        sitemap_rules = [
            ('/shop/', 'parse_shop'),
        ]

        other_urls = ['http://www.example.com/about']

        def start_requests(self):
            requests = list(super(MySpider, self).start_requests())
            requests += [Request(x, callback=self.parse_other) for x in self.other_urls]
            return requests

        def parse_shop(self, response):
            pass # ... scrape shop here ...

        def parse_other(self, response):
            pass # ... scrape other here ...

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