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):
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
parameter). Defaults to (‘href’,)
- canonicalize (boolean) – canonicalize each extracted url (using
scrapy.utils.url.canonicalize_url). Defaults to .
- unique (boolean) – whether duplicate filtering should be applied to extracted
links.
- process_value (callable) – see process_value argument of
BaseSgmlLinkExtractor 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
parameter). Defaults to (‘href’,)
- canonicalize (boolean) – canonicalize each extracted url (using
scrapy.utils.url.canonicalize_url). Defaults to .
- unique (boolean) – whether duplicate filtering should be applied to extracted
links.
- process_value (callable) – see process_value argument of
BaseSgmlLinkExtractor 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 if links should be extracted from
that tag, or False if they shouldn’t. Defaults to . 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 if
links should be extracted from it, or False if they shouldn’t.
Defaults to .
- 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 to ignore the link altogether. If not
given, process_value defaults to lambda .
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:
process_valuevalue
search"javascript:goToPage\('(.*?)'" value
return group
|