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

Tools

> 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

TODO

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

Web Scraper Shibuya.pm tech talk #8

1 comments

Notes on slide 1

5 Favorites & 3 Groups