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Link Extractors

Link extractors are objects whose only purpose is to extract links from web pages (:class:`scrapy.http.Response` objects) which will be eventually followed.

There is scrapy.linkextractors.LinkExtractor available in Scrapy, but you can create your own custom Link Extractors to suit your needs by implementing a simple interface.

The only public method that every link extractor has is extract_links, which receives a :class:`~scrapy.http.Response` object and returns a list of :class:`scrapy.link.Link` objects. Link extractors are meant to be instantiated once and their extract_links method called several times with different responses to extract links to follow.

Link extractors are used in the :class:`~scrapy.spiders.CrawlSpider` class (available in Scrapy), through a set of rules, but you can also use it in your spiders, even if you don't subclass from :class:`~scrapy.spiders.CrawlSpider`, as its purpose is very simple: to extract links.

Built-in link extractors reference

.. module:: scrapy.linkextractors
   :synopsis: Link extractors classes

Link extractors classes bundled with Scrapy are provided in the :mod:`scrapy.linkextractors` module.

The default link extractor is LinkExtractor, which is the same as :class:`~.LxmlLinkExtractor`:

from scrapy.linkextractors import LinkExtractor

There used to be other link extractor classes in previous Scrapy versions, but they are deprecated now.

LxmlLinkExtractor

.. module:: scrapy.linkextractors.lxmlhtml
   :synopsis: lxml's HTMLParser-based link extractors

LxmlLinkExtractor is the recommended link extractor with handy filtering options. It is implemented using lxml's robust HTMLParser.

param allow:

a single regular expression (or list of regular expressions) that the (absolute) urls must match in order to be extracted. If not given (or empty), it will match all links.
type allow:

a regular expression (or list of)
param deny:

a single regular expression (or list of regular expressions) that the (absolute) urls must match in order to be excluded (ie. not extracted). It has precedence over the allow parameter. If not given (or empty) it won't exclude any links.
type deny:

a regular expression (or list of)
param allow_domains:

a single value or a list of string containing domains which will be considered for extracting the links
type allow_domains:

str or list
param deny_domains:

a single value or a list of strings containing domains which won't be considered for extracting the links
type deny_domains:

str or list
param deny_extensions:

a single value or list of strings containing extensions that should be ignored when extracting links. If not given, it will default to the IGNORED_EXTENSIONS list defined in the scrapy.linkextractors package.
type deny_extensions:

list
param restrict_xpaths:

is an XPath (or list of XPath's) which defines regions inside the response where links should be extracted from. If given, only the text selected by those XPath will be scanned for links. See examples below.
type restrict_xpaths:

str or list
param restrict_css:

a CSS selector (or list of selectors) which defines regions inside the response where links should be extracted from. Has the same behaviour as restrict_xpaths.
type restrict_css:

str or list
param tags:

a tag or a list of tags to consider when extracting links. Defaults to ('a', 'area').
type tags:

str or list
param attrs:

an attribute or list of attributes which should be considered when looking for links to extract (only for those tags specified in the tags parameter). Defaults to ('href',)
type attrs:

list
param canonicalize:

canonicalize each extracted url (using w3lib.url.canonicalize_url). Defaults to False. Note that canonicalize_url is meant for duplicate checking; it can change the URL visible at server side, so the response can be different for requests with canonicalized and raw URLs. If you're using LinkExtractor to follow links it is more robust to keep the default canonicalize=False.
type canonicalize:

boolean
param unique:

whether duplicate filtering should be applied to extracted links.
type unique:

boolean
param process_value:

a function which receives each value extracted from the tag and attributes scanned and can modify the value and return a new one, or return None to ignore the link altogether. If not given, process_value defaults to lambda x: x.

For example, to extract links from this code:

<a href="javascript:goToPage('../other/page.html'); return false">Link text</a>

You can use the following function in process_value:

def process_value(value):
    m = re.search("javascript:goToPage\('(.*?)'", value)
    if m:
        return m.group(1)
type process_value:

callable
param strip:

whether to strip whitespaces from extracted attributes. According to HTML5 standard, leading and trailing whitespaces must be stripped from href attributes of <a>, <area> and many other elements, src attribute of <img>, <iframe> elements, etc., so LinkExtractor strips space chars by default. Set strip=False to turn it off (e.g. if you're extracting urls from elements or attributes which allow leading/trailing whitespaces).
type strip:

boolean