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I would like to get data from from different webpages such as addresses of restaurants or dates of different events for a given location and so on. What is the best library I can use for extracting this data from a given set of sites?
If using python, take a good look at Beautiful Soup (http://crummy.com/software/BeautifulSoup).
An extremely capable library, makes scraping a breeze.
The HTML Agility Pack For .net programers is awesome. It turns webpages in XML docs that can be queried with XPath.
HtmlDocument doc = new HtmlDocument();
doc.Load("file.htm");
foreach(HtmlNode link in doc.DocumentElement.SelectNodes("//a#href")
{
HtmlAttribute att = link"href";
att.Value = FixLink(att);
}
doc.Save("file.htm");
You can find it here. http://www.codeplex.com/htmlagilitypack
I think the general answer here is to use any language + http library + html/xpath parser. I find that using ruby + hpricot gives a nice clean solution:
require 'rubygems'
require 'hpricot'
require 'open-uri'
sites = %w(http://www.google.com http://www.stackoverflow.com)
sites.each do |site|
doc = Hpricot(open(site))
# iterate over each div in the document (or use xpath to grab whatever you want)
(doc/"div").each do |div|
# do something with divs here
end
end
For more on Hpricot see http://code.whytheluckystiff.net/hpricot/
I personally like the WWW::Mechanize Perl module for these kinds of tasks. It gives you an object that is modeled after a typical web browser, (i.e. you can follow links, fill out forms, or use the "back button" by calling methods on it).
For the extraction of the actual content, you could then hook it up to HTML::TreeBuilder to transform the website you're currently visiting into a tree of HTML::Element objects, and extract the data you want (the look_down() method of HTML::Element is especially useful).
i think watir or selenium are the best choices. Most of the other mentioned libraries are actually HTML parsers, and that is not what you want... You are scraping, if the owner of the website wanted you to get to his data he'd put a dump of his database or site on a torrent and avoid all the http requests and expensive traffic.
basically, you need to parse HTML, but more importantly automate a browser. This to the point of being able to move the mouse and click, basically really mimicking a user. You need to use a screencapture program to get to the captchas and send them off to decaptcha.com (that solve them for a fraction of a cent) to circumvent that. forget about saving that captcha file by parsing the html without rendering it in a browser 'as it is supposed to be seen'. You are screenscraping, not httprequestscraping.
watir did the trick for me in combination with autoitx (for moving the mouse and entering keys in fields -> sometimes this is necessery to set of the right javascript events) and a simple screen capture utility for the captcha's. this way you will be most succesfull, it's quite useless writing a great html parser to find out that the owner of the site has turned some of the text into graphics. (Problematic? no, just get an OCR library and feed the jpeg, text will be returned). Besides i have rarely seen them go that far, although on chinese sites, there is a lot of text in graphics.
Xpath saved my day all the time, it's a great Domain Specific Language (IMHO, i could be wrong) and you can get to any tag in the page, although sometimes you need to tweak it.
What i did miss was 'reverse templates' (the robot framework of selenium has this). Perl had this in CPAN module Template::Extract, very handy.
The html parsing, or the creation of the DOM, i would leave to the browser, yes, it won't be as fast, but it'll work all the time.
Also libraries that pretend to be Useragents are useless, sites are protected against scraping nowadays, and the rendering of the site on a real screen is often necessery to get beyond the captcha's, but also javascript events that need to be triggered for information to appear etc.
Watir if you're into Ruby, Selenium for the rest i'd say. The 'Human Emulator' (or Web Emulator in russia) is really made for this kind of scraping, but then again it's a russian product from a company that makes no secret of its intentions.
i also think that one of these weeks Wiley has a new book out on scraping, that should be interesting. Good luck...
I personally find http://github.com/shuber/curl/tree/master and http://simplehtmldom.sourceforge.net/ awesome for use in my PHP spidering/scraping projects.
The Perl WWW::Mechanize library is excellent for doing the donkey work of interacting with a website to get to the actual page you need.
I would use LWP (Libwww for Perl). Here's a good little guide: http://www.perl.com/pub/a/2002/08/20/perlandlwp.html
WWW::Scraper has docs here: http://cpan.uwinnipeg.ca/htdocs/Scraper/WWW/Scraper.html
It can be useful as a base, you'd probably want to create your own module that fits your restaurant mining needs.
LWP would give you a basic crawler for you to build on.
There have been a number of answers recommending Perl Mechanize, but I think that Ruby Mechanize (very similar to Perl's version) is even better. It handles some things like forms in a much cleaner way syntactically. Also, there are a few frontends which run on top of Ruby Mechanize which make things even easier.
What language do you want to use?
curl with awk might be all you need.
You can use tidy to convert it to XHTML, and then use whatever XML processing facilities your language of choice has available.
I'd recommend BeautifulSoup. It isn't the fastest but performs really well in regards to the not-wellformedness of (X)HTML pages which most parsers choke on.
what someone said.
use ANY LANGUAGE.
as long as you have a good parser library and http library, you are set.
the tree stuff are slower, then just using a good parse library.
Related
I'm looking for a library to parse HTML files in OCaml.
Basically the equivalent of Jsoup/Beautiful Soup.
The main requirement is being able to query the DOM with CSS selectors.
Something in the form of
page.fetch("http://www.url.com")
page.find("#tag")
I had a need for something like this recently, so after seeing this question and reading the recommendations in the comments, I wrote a library "Lambda Soup" over the weekend for fun.
You will want to use a library like ocurl or Cohttp to retrieve the actual HTML. After you have it, you can do
html |> parse $ "#tag"
to do what is asked in the question. For other possibilities and the full signature, see the documentation. You may want to look at the documentation postprocessor or tests for a fairly thorough demonstration of usage and capabilities, including CSS support and extensions.
Per comments, Lambda Soup uses Ocamlnet's HTML parser. Lambda Soup uses Markup.ml. Otherwise, it has no dependencies, except OUnit if you wish to run the tests. I'm happy for any feedback, including about modifying the interface (it is at an early stage) or discussions of adding an HTTP downloader to the library (which seems iffy because it greatly alters the scope of the library as it now is, but I am happy to hear arguments).
The license is BSD.
I'm processing a variety of RSS feeds, which contain summaries, as well as the target page URL content, and trying to use a uniform transformation method.
XSLT was the first thing that occurred to me to try, as it would accomplish what I want, in a standard way, without a lot of fuss aside from adding new XSLT stylesheets to accommodate uniquely formatted sites and feed content.
Problem: XSLT libraries are considered "private" in iOS, and even linking statically against your own copy will get you rejected by the Apple Store analysis tools.
I've looked into the possibility if injecting the stylesheet and data into a UIWebView that wasn't displayed, but this seems like a really roundabout and hackish way to get at the system's underlying XSLT processor in an "approved" fashion.
What alternative techniques/libraries exist which would let me do this in a standard fashion, ie: without rolling my own.
I'm not sure I fully understand your requirements, but one possbility would be to use libxml (which is allowed in iOS) to parse the XML and if necessary manipulate the DOM. If you really need to do XML transformations this is going to be more effort than XSLT, but if you just need to extract data from the XML, that can be done fairly easily with xpath queries.
That said, I have read several people claiming they got XSLT working on iOS and had their apps approved in the app store. In particular, I've seen this stackoverflow answer claimed as a working solution by multiple people. And if that fails, another answer suggested building the libxslt library yourself with renamed symbols to bypass the app store checks. I would only suggest that as a last resort though.
You'll probably want to look into Hpple for something powerful but light weight / native. See the tutorial on getting started here: http://www.raywenderlich.com/14172/how-to-parse-html-on-ios. Good luck!
I'm going to also recommend TFHpple but I'm also going to elaborate on the solution. I've explored an app that navigates a 3rd party (well, I'm the 3rd party, they're the source but that's semantics) website/data source but there are some pitfalls. The biggest pitfall is obvious: if the data source DOM changes you need to change your app and re-release. A creative way around this would be to publish/expose a global copy of the DOM on a public server that way the end user doesn't have to update their app any time the data source changes (as long as the change isn't radical).
For instance, if your expected DOM search in TFHpple is #"//figure[#class='figure']/a" and then a week from now your data source's resource you're looking for is altered to #"//figure1[#class='figure1']/a" you just opened yourself to an App Store release... UNLESS... you publish the expected DOM searches on a web server you control in a data dictionary that your app can consume and serve out to the various DOM search elements within your app. The only problem I foresee here is that if the data source adds or removes a data element you want to consume you either have to release a build or handle the removal ahead of time (respectively).
Lastly if the data source DOM isn't well formed or consistent you may be beating your head against a wall more times than not.
I have a large pile of lecture notes in raw HTML format. I would like to add interactive content to these notes, in particular incorporating online exercises. I have some experience implementing online exercises as cgi-bin executables compiled from Haskell code running on the server, interacting with a student record file and sending suitable HTML back to the browser, using Text.Xhtml to generate the content. Now I plan to integrate the notes and the exercises.
The trouble is that I don't want to spend ages manually transforming my raw HTML into Haskell code to generate exactly the raw HTML I started with. Instead, I'd like to put my Haskell code and my HTML in the same source file, with placeholders in the latter for content generated by the former. A suitable tool should then transform this file into Haskell source code for (e.g.) a cgi-bin executable which generates the corresponding page.
Before I go hacking up such a piece of kit, I thought I'd ask if there's better technology out there already. The fixed points are the large legacy lump of HTML, the need to implement the assessment of the exercises in Haskell, and the need to interact with student records on the server. The handicap is that I need to use the departmental web server and I can't reconfigure it (ok, maybe I could ask nicely): that's one of the reasons I currently use cgi-bin executables, which are just fine on our server already, but I'm open to other possibilities.
My current plan is to write a (I mean adapt an existing) preprocessor to support a special syntax for defining functions of type
Html -> ... -> Html -> Html
that looks a lot like raw HTML with splice points. Then what I do with my existing raw HTML is indent it a bit and mark the holes.
But would that be a waste of time? Please, please tell me that this question is a duplicate!
There are Haskell frameworks like Yesod and Happstack which use templating engines like you describe.
Have you looked at the haskell wiki at http://www.haskell.org/haskellwiki/HSP or
http://www.haskell.org/haskellwiki/Web/Libraries/Templating ?
They may do what you need.
You might find someting to do the job here: Templating packages for Haskell.
And you should probably look into Snap, Yesod or Happstack for serving the content.
I have a large pile of lecture notes in raw HTML format. I would like to add interactive content to these notes, in particular incorporating online exercises.
There is already a system (called "ActiveHs"), written in Haskell, that allows to put lecture notes and interactive exercises in one file.
See:
http://pnyf.inf.elte.hu/fp/UsersGuide_en.xml
http://pnyf.inf.elte.hu/fp/Constructive_en.xml
I can really say that it is very well written code and completely open source!
I am writing a crawler in Perl, which has to extract contents of web pages that reside on the same server. I am currently using the HTML::Extract module to do the job, but I found the module a bit slow, so I looked into its source code and found out it does not use any connection cache for LWP::UserAgent.
My last resort is to grab HTML::Extract's source code and modify it to use a cache, but I really want to avoid that if I can. Does anyone know any other module that can perform the same job better? I basically just need to grab all the text in the <body> element with the HTML tags removed.
I use pQuery for my web scraping. But I've also heard good things about Web::Scraper.
Both of these along with other modules have appeared in answers on SO for similar questions to yours:
how can i screen scrape with perl
how can i extract xml of a website and save in a file using perls lwp
how do i extract an html title with perl
can you provide an example of parsing html with your favorite parser
how do I extract content from html file using perl
HTML::Extract's features look very basic and uninteresting. If the modules that draegfun mentioned don't interest you, you could do everything that HTML::Extract does using LWP::UserAgent and HTML::TreeBuilder yourself, without requiring very much code at all, and then you would be free to work in caching on your own terms.
I've been using Web::Scraper for my scraping needs. It's very nice indeed for extracting data, and because you can call ->scrape($html, $originating_uri) then it's very easy to cache the result you need as well.
Do you need to do this in real-time? How does the inefficiency affect you? Are you doing the task serially so that you have to extract one page before you move onto the next one? Why do you want to avoid a cache?
Can your crawler download the pages and pass them off to something else? Perhaps your crawler can even run in parallel, or in some distributed manner.
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I want to highlight C/C++/Java/C# etc source codes in my website.
How can I do this?
Is it a CPU intensive job to highlight the source code?
You can either do this server-side or client-side. It's not very processor intensive, but if you do it client side (using Javascript) there will be a noticeable lag. Most client side solutions revolve around Google Code's syntax highlighting engine. This seems to be the most popular one: SyntaxHighlighter
Server-side solutions tend to be more flexible, especially in the way of defining new languages and configuring how they are highlighted (e.g. colors used). I use GeSHi, which is a PHP solution with a moderately nice plugin for Wordpress. There are also a few libraries built for Java, and even some that are based upon VIM (usually requiring a Perl module to be installed from CPAN).
In short: you have quite a few options, what are your criteria? It's hard to make a solid recommendation without knowing your requirements.
I use GeSHi ("Generic Syntax Highlighter") on pastebin.com
pastebin has high traffic, so I do cache the results of the transformation, which certainly reduces the load.
Personally, I prefer offline tools: I don't see the point of parsing the code (particularly large ones) over and over, for each served page, or even worse, on each browser (for JS libraries), because as pointed above, these libraries often lag (you often see raw source before it is formatted).
There are a number of tools to do this job, some pointed above. I just use the export feature of my favorite editor (SciTE) because it just respects the choices of color I carefully set up... :-) And it can output XML, PDF, RTF and LaTeX too.
Pygment is a good Python library to generate HTML, RTF, ANSI (terminal-style) or LaTeX code. It supports a large range of languages (C, C++, Lua, Erlang, ...) and you can even write your own output formatter.
I use google-code-prettify. It is the simplest to set up and works great with all C-style languages.
If you use jEdit, you might want to use the Code2HTML plugin.
I use SyntaxHighligher on my blog.
Just run it through a tool like: http://www.gnu.org/software/src-highlite/
If you are using PHP, you can use GeSHi to highlight many different languages. I've used it before and it works quite well. A quick googling will also uncover GeSHi plugins for wordpress and drupal.
I wouldn't consider highlighting to be CPU intensive unless you are intending to display megabytes of it all at once. And even then, the CPU load would be minimal and your main problem would be transfer speed for it all.