Link Extractors¶
LinkExtractors are objects whose only purpose is to extract links from web
pages (scrapy.http.Response
objects) which will be eventually
followed.
There are two Link Extractors available in Scrapy by default, but you create your own custom Link Extractors to suit your needs by implementing a simple interface.
The only public method that every LinkExtractor has is extract_links
,
which receives a Response
object and returns a list
of 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 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
CrawlSpider
, as its purpose is very simple: to
extract links.
Built-in link extractors reference¶
All available link extractors classes bundled with Scrapy are provided in the
scrapy.contrib.linkextractors
module.
If you don’t know what link extractor to choose, just use the default which is the same as LxmlLinkExtractor (see below):
from scrapy.contrib.linkextractors import LinkExtractor
LxmlLinkExtractor¶
-
class
scrapy.contrib.linkextractors.lxmlhtml.
LxmlLinkExtractor
(allow=(), deny=(), allow_domains=(), deny_domains=(), deny_extensions=None, restrict_xpaths=(), tags=('a', 'area'), attrs=('href', ), canonicalize=True, unique=True, process_value=None)¶ LxmlLinkExtractor is the recommended link extractor with handy filtering options. It is implemented using lxml’s robust HTMLParser.
Parameters: - allow (a regular expression (or list of)) – 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.
- deny (a regular expression (or list of)) – 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. - allow_domains (str or list) – a single value or a list of string containing domains which will be considered for extracting the links
- deny_domains (str or list) – a single value or a list of strings containing domains which won’t be considered for extracting the links
- deny_extensions (list) – 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.linkextractor module. - restrict_xpaths (str or list) – is a 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.
- tags (str or list) – a tag or a list of tags to consider when extracting links.
Defaults to
('a', 'area')
. - attrs (list) – 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',)
- canonicalize (boolean) – canonicalize each extracted url (using
scrapy.utils.url.canonicalize_url). Defaults to
True
. - unique (boolean) – whether duplicate filtering should be applied to extracted links.
- process_value (callable) – see
process_value
argument ofBaseSgmlLinkExtractor
class constructor
SgmlLinkExtractor¶
Warning
SGMLParser based link extractors are unmantained and its usage is discouraged.
It is recommended to migrate to LxmlLinkExtractor
if you are still
using SgmlLinkExtractor
.
-
class
scrapy.contrib.linkextractors.sgml.
SgmlLinkExtractor
(allow=(), deny=(), allow_domains=(), deny_domains=(), deny_extensions=None, restrict_xpaths=(), tags=('a', 'area'), attrs=('href'), canonicalize=True, unique=True, process_value=None)¶ The SgmlLinkExtractor is built upon the base
BaseSgmlLinkExtractor
and provides additional filters that you can specify to extract links, including regular expressions patterns that the links must match to be extracted. All those filters are configured through these constructor parameters:Parameters: - allow (a regular expression (or list of)) – 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.
- deny (a regular expression (or list of)) – 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. - allow_domains (str or list) – a single value or a list of string containing domains which will be considered for extracting the links
- deny_domains (str or list) – a single value or a list of strings containing domains which won’t be considered for extracting the links
- deny_extensions (list) – 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.linkextractor module. - restrict_xpaths (str or list) – is a 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.
- tags (str or list) – a tag or a list of tags to consider when extracting links.
Defaults to
('a', 'area')
. - attrs (list) – 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',)
- canonicalize (boolean) – canonicalize each extracted url (using
scrapy.utils.url.canonicalize_url). Defaults to
True
. - unique (boolean) – whether duplicate filtering should be applied to extracted links.
- process_value (callable) – see
process_value
argument ofBaseSgmlLinkExtractor
class constructor
BaseSgmlLinkExtractor¶
-
class
scrapy.contrib.linkextractors.sgml.
BaseSgmlLinkExtractor
(tag="a", attr="href", unique=False, process_value=None)¶ The purpose of this Link Extractor is only to serve as a base class for the
SgmlLinkExtractor
. You should use that one instead.The constructor arguments are:
Parameters: - tag (str or callable) – either a string (with the name of a tag) or a function that
receives a tag name and returns
True
if links should be extracted from that tag, orFalse
if they shouldn’t. Defaults to'a'
. request (once it’s downloaded) as its first parameter. For more information, see Passing additional data to callback functions. - attr (str or callable) – either string (with the name of a tag attribute), or a
function that receives an attribute name and returns
True
if links should be extracted from it, orFalse
if they shouldn’t. Defaults tohref
. - unique (boolean) – is a boolean that specifies if a duplicate filtering should be applied to links extracted.
- process_value (callable) –
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 tolambda 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)
- tag (str or callable) – either a string (with the name of a tag) or a function that
receives a tag name and returns