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 import 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.
.. module:: scrapy.linkextractors
:synopsis: Link extractors classesLink 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 LinkExtractorThere used to be other link extractor classes in previous Scrapy versions, but they are deprecated now.
.. 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 |
| 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
|
| 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 |
| type restrict_css: | str or list |
| param tags: | a tag or a list of tags to consider when extracting links.
Defaults to |
| 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 |
| type attrs: | list |
| param canonicalize: | canonicalize each extracted url (using
scrapy.utils.url.canonicalize_url). Defaults to |
| 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 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 def process_value(value):
m = re.search("javascript:goToPage\('(.*?)'", value)
if m:
return m.group(1) |
| type process_value: | callable |