Web Scraper Shibuya.pm tech talk #8

Practical Web Scraping with Web::Scraper Tatsuhiko Miyagawa [email_address] Six Apart, Ltd. / Shibuya Perl Mongers Shibuya.pm Tech Talks #8

Practical Web Scraping
with Web::Scraper

Web pages are built using text-based mark-up languages ( HTML and XHTML ), and frequently contain a wealth of useful data in text form. However, most web pages are designed for human consumption, and frequently mix content with presentation. Thus, screen scrapers were reborn in the web era to extract machine-friendly data from HTML and other markup. http://en.wikipedia.org/wiki/Screen_scraping

"Screen-scraping
is so 1999!"

RSS is a metadata
not a complete
HTML replacement

with Web::Scraper

What's wrong with
LWP & Regexp?

<td>Current UTC (or GMT/Zulu)-time used: Monday, August 27, 2007 at 12:49:46

<td>Current UTC (or GMT/Zulu)-time used: Monday, August 27, 2007 at 12:49:46 > perl -MLWP::Simple -le '$c = get("http://timeanddate.com/worldclock/"); $c =~ m@(.*?)@ and print $1' Monday, August 27, 2007 at 12:49:46

It works!

WWW::MySpace 0.70

WWW::Search::Ebay 2.231

WWW::Mixi 0.50

It works …

There are
3 problems
(at least)

(1)
Fragile
Easy to break even with slight HTML changes
(like newlines, order of attributes etc.)

(2)
Hard to maintain
Regular expression based scrapers are good
Only when they're used in write-only scripts

(3)
Improper
HTML & encoding
handling

I &hearts; Shibuya > perl –e '$c =~ m@(.*?)@ and print $1' I &hearts; Shibuya

I &hearts; Shibuya > perl –MHTML::Entities –e '$c =~ m@(.*?)@ and print decode_entities ($1)' I ♥ Shibuya

Perl が大好き！ > perl –MHTML::Entities –MEncode –e '$c =~ m@(.*?)@ and print decode_entities( decode_utf8 ($1))' Wide character in print at –e line 1. Perl が大好き！

The "right" way
of screen-scraping

(1), (2)
Maintainable
Less fragile

Use XPath
and CSS Selectors

XPath
HTML::TreeBuilder::XPath
XML::LibXML

XPath <td>Current UTC (or GMT/Zulu)-time used: Monday, August 27, 2007 at 12:49:46 use HTML::TreeBuilder::XPath; my $tree = HTML::TreeBuilder::XPath->new_from_content($content); print $tree->findnodes ('//strong[@id="ctu"]') ->shift->as_text; # Monday, August 27, 2007 at 12:49:46

CSS Selectors
"XPath for HTML coders"
"XPath for people who hates XML"

CSS Selectors
body { font-size: 12px; }
div.article { padding: 1em }
span#count { color: #fff }

XPath:
//strong[@id="ctu"]
CSS Selector:
strong#ctu

CSS Selectors <td>Current UTC (or GMT/Zulu)-time used: Monday, August 27, 2007 at 12:49:46 use HTML::TreeBuilder::XPath; use HTML::Selector::XPath qw(selector_to_xpath); my $tree = HTML::TreeBuilder::XPath->new_from_content($content); my $xpath = selector_to_xpath "strong#ctu"; print $tree->findnodes($xpath)->shift->as_text; # Monday, August 27, 2007 at 12:49:46

Complete Script #!/usr/bin/perl use strict; use warnings; use Encode; use LWP::UserAgent; use HTTP::Response::Encoding; use HTML::TreeBuilder::XPath; use HTML::Selector::XPath qw(selector_to_xpath); my $ua = LWP::UserAgent->new; my $res = $ua->get("http://www.timeanddate.com/worldclock/"); if ($res->is_error) { die "HTTP GET error: ", $res->status_line; } my $content = decode $res->encoding, $res->content; my $tree = HTML::TreeBuilder::XPath->new_from_content($content); my $xpath = selector_to_xpath("strong#ctu"); my $node = $tree->findnodes($xpath)->shift; print $node->as_text;

Robust,
Maintainable,
and
Sane character handling

Exmaple (before) <td>Current UTC (or GMT/Zulu)-time used: Monday, August 27, 2007 at 12:49:46 > perl -MLWP::Simple -le '$c = get("http://timeanddate.com/worldclock/"); $c =~ m@(.*?)@ and print $1' Monday, August 27, 2007 at 12:49:46

Example (after) #!/usr/bin/perl use strict; use warnings; use Encode; use LWP::UserAgent; use HTTP::Response::Encoding; use HTML::TreeBuilder::XPath; use HTML::Selector::XPath qw(selector_to_xpath); my $ua = LWP::UserAgent->new; my $res = $ua->get("http://www.timeanddate.com/worldclock/"); if ($res->is_error) { die "HTTP GET error: ", $res->status_line; } my $content = decode $res->encoding, $res->content; my $tree = HTML::TreeBuilder::XPath->new_from_content($content); my $xpath = selector_to_xpath("strong#ctu"); my $node = $tree->findnodes($xpath)->shift; print $node->as_text;

but …
long and boring

with Web::Scraper

Web scraping toolkit
inspired by scrapi.rb
DSL-ish

Example (before) #!/usr/bin/perl use strict; use warnings; use Encode; use LWP::UserAgent; use HTTP::Response::Encoding; use HTML::TreeBuilder::XPath; use HTML::Selector::XPath qw(selector_to_xpath); my $ua = LWP::UserAgent->new; my $res = $ua->get("http://www.timeanddate.com/worldclock/"); if ($res->is_error) { die "HTTP GET error: ", $res->status_line; } my $content = decode $res->encoding, $res->content; my $tree = HTML::TreeBuilder::XPath->new_from_content($content); my $xpath = selector_to_xpath("strong#ctu"); my $node = $tree->findnodes($xpath)->shift; print $node->as_text;

Example (after)
#!/usr/bin/perl
use strict;
use warnings;
use Web::Scraper;
use URI;
my $s = scraper {
process "strong#ctu", time => 'TEXT';
result 'time';
};
my $uri = URI->new("http://timeanddate.com/worldclock/");
print $s->scrape($uri);

Basics
use Web::Scraper;
my $s = scraper {
# DSL goes here
};
my $res = $s->scrape($uri);

process
process $selector,
$key => $what,
… ;

$selector:
CSS Selector
or
XPath (start with /)

$key:
key for the result hash
append "[]" for looping

$what:
'@attr'
'TEXT'
'RAW'
Web::Scraper
sub { … }
Hash reference

<ul class="sites"> <li><a href="http://vienna.openguides.org/">OpenGuides</a></li> <li><a href="http://vienna.yapceurope.org/">YAPC::Europe</a></li> </ul>

process "ul.sites > li > a",
'urls[]' => ' @href ';
# { urls => [ … ] }
<ul class="sites"> <li><a href=" http://vienna.openguides.org/ ">OpenGuides</a></li> <li><a href=" http://vienna.yapceurope.org/ ">YAPC::Europe</a></li> </ul>

process '//ul[@class="sites"]/li/a',
'names[]' => ' TEXT ';
# { names => [ 'OpenGuides', … ] }
<ul class="sites"> <li><a href="http://vienna.openguides.org/"> OpenGuides </a></li> <li><a href="http://vienna.yapceurope.org/"> YAPC::Europe </a></li> </ul>

process "ul.sites > li",
'sites[]' => scraper {
process 'a',
link => '@href', name => 'TEXT';
};
# { sites => [ { link => …, name => … },
# { link => …, name => … } ] };

'sites[]' => sub {
# $_ is HTML::Element
+{ link => $_->attr('href'), name => $_->as_text };
};
# { sites => [ { link => …, name => … },
# { link => …, name => … } ] };

'sites[]' => {
link => '@href', name => 'TEXT';
};
# { sites => [ { link => …, name => … },
# { link => …, name => … } ] };

result
result;
# get stash as hashref (default)
result @keys;
# get stash as hashref containing @keys
result $key;
# get value of stash $key;
my $s = scraper { process …; process …; result 'foo', 'bar'; };

Live Demo

> cpan Web::Scraper
comes with 'scraper' CLI

> scraper http://example.com/
scraper> process "a", "links[]" => '@href';
scraper> d
$VAR1 = {
links => [
'http://example.org/',
'http://example.net/',
],
};
scraper> y
---
links:
- http://example.org/
- http://example.net/

> scraper /path/to/foo.html
> GET http://example.com/ | scraper

Recent Updates

0.13
'c' and 'c all'
WARN in scraper

0.14
automatic absolute URI for link elements (a@href, img@src)

0.14 (cont.)
'RAW' and 'HTML'

0.15
$Web::Scraper::UserAgent
$scraper->user_agent

0.19
support encoding detection w/ META tags

Web::Scraper
Needs documentation

More examples
to put in eg/ directory

Alternative API
inspired by scRUBYt!

OO Backend API
if you don't like the DSL

integrate with
WWW::Mechanize
and Test::WWW::Declare

XPath Auto-suggestion
off of DOM + element
DOM + XPath => Element
DOM + Element => XPath?
(Template::Extract?)

generic XML support
(e.g. RSS/Atom feeds)

extensible text filter
date, geo, hCards (microformats)
October 1st, 2007 17:13:31 +0900 process ".entry-date", date => 'TEXT :rfc822 ';

Summary

Web::Scraper
inspired by scrapi

easy, fun, maintainable
& less fragile

CSS selector
XPath

Questions?

Thank you
http://search.cpan.org/dist/Web-Scraper
http://www.slideshare.net/miyagawa/webscraper

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Web Scraper Shibuya.pm tech talk #8

by Tatsuhiko Miyagawa on Oct 01, 2007

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Web Scraper Shibuya.pm tech talk #8 — Presentation Transcript