Perl Bloom::Filter与Web::Scraper

安装Bloom::Filter之前要先安装Digest::SHA1

#!/usr/bin/perl
use Bloom::Filter;
my $bf=Bloom::Filter->new(capacity => 10,error_rate => .001);
my @keys=qw/a s d f g h j k l z/;
$bf->add(@keys);
while(<>){
??? chomp;
??? print "Found $_n" if $bf->check($_);
}

$bf=Bloom::Filter->new(capacity => 10,error_rate => .001);

创建一个Bloom::Filter，其最大容量为10,判断某一个元素是否在容器中的最大出错概率为0.001。

$bf->add(@keys); 向容器中添加元素。

$bf->check($_)

判断某一个元素是否在容器中。

<<===========================================================================>>

快速掠一下下面的代码，初次看是很难看懂。

use URI;
use Web::Scraper;

# First,create your scraper block
my $tweets = scraper {
???? # Parse all LIs with the class "status",store them into a resulting
???? # array 'tweets'.? We embed another scraper for each tweet.
???? process "li.status","tweets[]" => scraper {
???????? # And,in that array,pull in the elementy with the class
???????? # "entry-content","entry-date" and the link
???????? process ".entry-content",body => 'TEXT';
???????? process ".entry-date",when => 'TEXT';
???????? process 'a[rel="bookmark"]',link => '@href';
???? };
?};

?my $res = $tweets->scrape( URI->new("http://twitter.com/miyagawa") );

?# The result has the populated tweets array
?for my $tweet (@{$res->{tweets}}) {
???? print "$tweet->{body} $tweet->{when} (link: $tweet->{link})n";
?}

The structure would resemble this (visually)
?{
?? tweets => [
???? { body => $body,when => $date,link => $uri },
???? { body => $body,
?? ]
?}

Web::Scaper是一组用来提取HTML文档中元素内容的工具集，它能够理解HTML和CSS选择器以及XPath表达式。

$res = $scraper->scrape(URI->new($uri));
$res = $scraper->scrape($html_content);?
$res = $scraper->scrape($html_content);?
$res = $scraper->scrape($http_response);?
$res = $scraper->scrape($html_element);

如果你传入的参数是URI或HTTP response，那Web::Scaper自动去寻找Content-Type header和META标签以判断文件编码。否则你压根先把HTML内容解码为Unicode后再传给scape函数。

当你把HTML内容作为参数传给scrape函数时，你还要考虑一个问题：HTML文档中出现?相对路径怎么办？所以这个时候你可以把base url一并作为参数传进去。

$res = $scraper->scrape($html_content,"http://example.com/foo");

process函数用来根据给定的HTML或CSS选择器或XPath表达式来匹配元素，把text或attributes抽取到result中。

scraper { process "tag.class",key => 'TEXT';

　　　　process '//tag[contains(@foo,"bar")]',key2 => '@attr';

};

它有两个参数，当第一个参数以"//"或"id("开头时作为XPath对待；否则作为HTML或CSS选择器对待。

# <span class="date">2008/12/21</span># date => "2008/12/21"process ".date",date => 'TEXT';　　　　# CSS的class是date# <div class="body"><a href="http://example.com/">foo</a></div># link => URI->new("http://example.com/")process ".body > a",link => '@href';　　　　# href是个属性# <div class="body"><a href="http://example.com/">foo</a></div># link => URI->new("http://example.com/"),text => "foo"process ".body > a",link => '@href',text => 'TEXT';　　# TEXT指标签内真正的内容# <ul><li>foo</li><li>bar</li></ul># list => [ "foo","bar" ]process "li","list[]" => "TEXT";　　　　# []返回数组# <ul><li id="1">foo</li><li id="2">bar</li></ul># list => [ { id => "1",text => "foo" },{ id => "2",text => "bar" } ];process "li","list[]" => { id => '@id',text => "TEXT" };　　　　#返回散列数组