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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 trying to figure out how to parse HTML to XML, but I cannot figure it out. I want to use the MSXML2.ServerXMLHTTP object (in an .asp file).
<%
url = "http://www.website.com/file.asp"
set xmlhttp = CreateObject("MSXML2.ServerXMLHTTP")
xmlhttp.open "POST", url, false
xmlhttp.send
Response.write xmlhttp.responseText
set xmlhttp = nothing
%>
This gives me the text, but I really don't know where to go from here.
I think problem is in HEAD of HTML file.
From MSDN: resonse should return XML ("text/xml"), but your http://www.website.com/file.asp returns HTML content, with ("text/html") mime type.
Native XML Extensions
I prefer using one of the native XML extensions since they come bundled with PHP, are usually faster than all the 3rd party libs and give me all the control I need over the markup.
DOM
The DOM extension allows you to operate on XML documents through the DOM API with PHP 5. It is an implementation of the W3C's Document Object Model Core Level 3, a platform- and language-neutral interface that allows programs and scripts to dynamically access and update the content, structure and style of documents.
DOM is capable of parsing and modifying real world (broken) HTML and it can do XPath queries. It is based on libxml.
It takes some time to get productive with DOM, but that time is well worth it IMO. Since DOM is a language-agnostic interface, you'll find implementations in many languages, so if you need to change your programming language, chances are you will already know how to use that language's DOM API then.
A basic usage example can be found in grabbing the href attribute of an A element and a general conceptual overview can be found at DOMDocument in PHP.
How to use the DOM extension has been covered extensively on StackOverflow, so if you choose to use it, you can be sure most of the issues you run into can be solved by searching/browsing StackOverflow.
XMLReader
The XMLReader extension is an XML pull parser. The reader acts as a cursor going forward on the document stream and stopping at each node on the way.
XMLReader, like DOM, is based on libxml. I am not aware of how to trigger the HTML Parser Module, so chances are using XMLReader for parsing broken HTML might be less robust than using DOM where you can explicitly tell it to use libxml's HTML parser module.
A basic usage example can be found at getting all values from h1 tags using PHP.
XML Parser
This extension lets you create XML parsers and then define handlers for different XML events. Each XML parser also has a few parameters you can adjust.
The XML Parser library is also based on libxml, and implements a SAX style XML push parser. It may be a better choice for memory management than DOM or SimpleXML, but will be more difficult to work with than the pull parser implemented by XMLReader.
SimpleXml
The SimpleXML extension provides a very simple and easily usable toolset to convert XML to an object that can be processed with normal property selectors and array iterators.
SimpleXML is an option when you know the HTML is valid XHTML. If you need to parse broken HTML, don't even consider SimpleXml because it will choke.
A basic usage example can be found at A simple program to CRUD node and node values of xml file and there is lots of additional examples in the PHP manual.
3rd Party Libraries (libxml based)
If you prefer to use a 3rd-party lib, I'd suggest using a lib that actually uses DOM/libxml underneath instead of string parsing.
FluentDom - Repo
FluentDOM provides a jQuery-like fluent XML interface for the DOMDocument in PHP. Selectors are written in XPath or CSS (using a CSS to XPath converter). Current versions extend the DOM implementing standard interfaces and add features from the DOM Living Standard. FluentDOM can load formats like JSON, CSV, JsonML, RabbitFish and others. Can be installed via Composer.
HtmlPageDom
Wa72\HtmlPageDom` is a PHP library for easy manipulation of HTML documents using It requires DomCrawler from Symfony2 components for traversing the DOM tree and extends it by adding methods for manipulating the DOM tree of HTML documents.
phpQuery (not updated for years)
phpQuery is a server-side, chainable, CSS3 selector driven Document Object Model (DOM) API based on jQuery JavaScript Library written in PHP5 and provides additional Command Line Interface (CLI).
Also see: https://github.com/electrolinux/phpquery
Zend_Dom
Zend_Dom provides tools for working with DOM documents and structures. Currently, we offer Zend_Dom_Query, which provides a unified interface for querying DOM documents utilizing both XPath and CSS selectors.
QueryPath
QueryPath is a PHP library for manipulating XML and HTML. It is designed to work not only with local files, but also with web services and database resources. It implements much of the jQuery interface (including CSS-style selectors), but it is heavily tuned for server-side use. Can be installed via Composer.
fDOMDocument
fDOMDocument extends the standard DOM to use exceptions at all occasions of errors instead of PHP warnings or notices. They also add various custom methods and shortcuts for convenience and to simplify the usage of DOM.
sabre/xml
sabre/xml is a library that wraps and extends the XMLReader and XMLWriter classes to create a simple "XML to object/array" mapping system and design pattern. Writing and reading XML is single-pass and can therefore be fast and require low memory on large XML files.
FluidXML
FluidXML is a PHP library for manipulating XML with a concise and fluent API. It leverages XPath and the fluent programming pattern to be fun and effective.
3rd-Party (not libxml-based)
The benefit of building upon DOM/libxml is that you get good performance out of the box because you are based on a native extension. However, not all 3rd-party libs go down this route. Some of them listed below.
PHP Simple HTML DOM Parser
An HTML DOM parser written in PHP5+ lets you manipulate HTML in a very easy way!
Require PHP 5+.
Supports invalid HTML.
Find tags on an HTML page with selectors just like jQuery.
Extract contents from HTML in a single line.
I generally do not recommend this parser. The codebase is horrible and the parser itself is rather slow and memory hungry. Not all jQuery Selectors (such as child selectors) are possible. Any of the libxml based libraries should outperform this easily.
PHP Html Parser
PHPHtmlParser is a simple, flexible, HTML parser which allows you to select tags using any CSS selector, like jQuery. The goal is to assist in the development of tools which require a quick, easy way to scrape HTML, whether it's valid or not! This project was original supported by sunra/php-simple-html-dom-parser but the support seems to have stopped so this project is my adaptation of his previous work.
Again, I would not recommend this parser. It is rather slow with high CPU usage. There is also no function to clear memory of created DOM objects. These problems scale particularly with nested loops. The documentation itself is inaccurate and misspelled, with no responses to fixes since 14 Apr 16.
Ganon
A universal tokenizer and HTML/XML/RSS DOM parser
Ability to manipulate elements and their attributes
Supports invalid HTML and UTF8
Can perform advanced CSS3-like queries on elements (like jQuery -- namespaces supported)
A HTML beautifier (like HTML Tidy)
Minify CSS and Javascript
Sort attributes, change character case, correct indentation, etc.
Extensible
Parsing documents using callbacks based on current character/token
Operations separated in smaller functions for easy overriding
Fast and easy
Never used it. Can't tell if it's any good.
HTML 5
You can use the above for parsing HTML5, but there can be quirks due to the markup HTML5 allows. So for HTML5 you want to consider using a dedicated parser, like:
html5lib
A Python and PHP implementations of a HTML parser based on the WHATWG HTML5 specification for maximum compatibility with major desktop web browsers.
We might see more dedicated parsers once HTML5 is finalized. There is also a blogpost by the W3's titled How-To for html 5 parsing that is worth checking out.
WebServices
If you don't feel like programming PHP, you can also use Web services. In general, I found very little utility for these, but that's just me and my use cases.
ScraperWiki
ScraperWiki's external interface allows you to extract data in the form you want for use on the web or in your own applications. You can also extract information about the state of any scraper.
Regular Expressions
Last and least recommended, you can extract data from HTML with regular expressions. In general using Regular Expressions on HTML is discouraged.
Most of the snippets you will find on the web to match markup are brittle. In most cases they are only working for a very particular piece of HTML. Tiny markup changes, like adding whitespace somewhere, or adding, or changing attributes in a tag, can make the RegEx fails when it's not properly written. You should know what you are doing before using RegEx on HTML.
HTML parsers already know the syntactical rules of HTML. Regular expressions have to be taught for each new RegEx you write. RegEx are fine in some cases, but it really depends on your use-case.
You can write more reliable parsers, but writing a complete and reliable custom parser with regular expressions is a waste of time when the aforementioned libraries already exist and do a much better job on this.
Also see Parsing Html The Cthulhu Way
Books
If you want to spend some money, have a look at
PHP Architect's Guide to Webscraping with PHP
I am not affiliated with PHP Architect or the authors.
How does one study open-source libraries code, particularly standard libraries?
The code base is often vast and hard to navigate. How to find some function or class definition?
Do I search through downloaded source files?
Do I need cvs/svn for that?
Maybe web-search?
Should I just know the structure of the standard library?
Is there any reference on it?
Or do some IDEs have such features? Or some other tools?
How to do it effectively without one?
What are the best practices of doing this in any open-source libraries?
Is there any convention of how are sources manipulated on Linux/Unix systems?
What are the differences for specific programming languages?
Broad presentation of the subject is highly encouraged.
I mark this 'community wiki' so everyone can rephrase and expand my awkward formulations!
Update: Probably didn't express the problem clear enough. What I want to, is to view just the source code of some specific library class or function. And the problem is mostly about work organization and usability - how do I navigate in the huge pile of sources to find the thing, maybe there are specific tools or approaches? It feels like there should've long existed some solution(s) for that.
One thing to note is that standard libraries are sometimes (often?) optimized more than is good for most production code.
Because they are widely used, they have to perform well over a wide variety of conditions, and may be full of clever tricks and special logic for corner cases.
Maybe they are not the best thing to study as a beginner.
Just a thought.
Well, I think that it's insane to just site down and read a library's code. My approach is to search whenever I come across the need to implement something by myself and then study the way that it's implemented in those libraries.
And there's also allot of projects/libraries with excellent documentation, which I find more important to read than the code. In Unix based systems you often find valuable information in the man pages.
Wow, that's a big question.
The short answer: it depends.
The long answer:
Some libraries provide documentation while others don't. Standard libraries are usually pretty well documented, whether your chosen implementation of the library includes documentation or not. For instance you may have found an implementation of the c standard library without documentation but the c standard has been around long enough that there are hundreds of good reference books available. Documentation with hyperlinks is a very useful way to learn a new API. In any case the first place I would look is the library's main website
For less well known libraries lacking documentation I find two different approaches very helpful.
First is a doc generator. Nearly every language I know of has one. It basically parses an source tree and creates documentation (usually as html or xml) which can be used to learn a library. Some use specially formatted comments in the code to create more complete documentation. JavaDoc is one good example of this. Doc generators for many other languages borrow from JavaDoc.
Second an IDE with a class browser. These act as a sort of on the fly documentation. Some display just the library's interface. Other's include description comments from the library's source.
Both of these will require access to the libraries source (which will come in handy if you intend actually use a library).
Many of these tools and techniques work equally well for closed/proprietary libraries.
The standard Java libraries' source code is available. For a beginning Java programmer these can be a great read. Especially the Collections framework is a good place to start. Take for instance the implementation of ArrayList and learn how you can implement a resizeable array in Java. Most of the source has even useful comments.
The best parts to read are probably whose purpose you can understand immediately. Start with the easy pieces and try to follow all the steps that are hidden behind that single call you make from your own code.
Something I do from time to time :
apt-get source foo
Then new C++ project (or whatever) in Eclipse and import.
=> Wow ! Browsable ! (use F3)
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Is DOM the only way to parse JSON?
Some JSON parsers do offer incremental ("streaming") parser; for Java, at least following parsers from json.org page offer such an interface:
Jackson (pull interface)
Json-simple (SAX-style push interface)
(in addition to Software Monkey's parser referred to by another answer)
Actually, it is kind of odd that so many JSON parsers do NOT offer this simple low-level interface -- after all, they already need to implement low-level parsing, so why not expose it.
EDIT (June 2011): Gson too has its own streaming API (with gson 1.6)
By DOM, I assume you mean that the parser reads an entire document at once before you can work with it. Note that saying DOM tends to imply XML, these days, but IMO that is not really an accurate inference.
So, in answer to your questions - "Yes", there are streaming API's and "No", DOM is not the only way. That said, processing a JSON document as a stream is often problematic in that many objects are not simple field/value pairs, but contain other objects as values, which you need to parse to process, and this tends to end up a recursive thing. But for simple messages you can do useful things with a stream/event based parser.
I have written a pull-event parser for JSON (it was one class, about 700 lines). But most of the others I have seen are document oriented. One of the layers I have built on top of my parser is a document reader, which took about 30 LOC. I have only ever used my parser in practice as a document loader (for the above reason).
I am sure if you search the net you will find pull and push based parsers for JSON.
EDIT: I have posted the parser to my site for download. A working compilable class and a complete example are included.
EDIT2: You'll also want to look at the JSON website.
As stefanB mentioned, http://lloyd.github.com/yajl/ is a C library for stream parsing JSON. There are also many wrappers mentioned on that page for other languages:
yajl-ruby - ruby bindings for YAJL
yajl-objc - Objective-C bindings for YAJL
YAJL IO bindings (for the IO language)
Python bindings come in two flavors, py-yajl OR yajl-py
yajl-js - node.js bindings (mirrored to github).
lua-yajl - lua bindings
ooc-yajl - ooc bindings
yajl-tcl - tcl bindings
some of them may not allow streaming, but many of them certainly do.
If you want to use pure javascript and a library that runs both in node.js and in the browser you can try clarinet:
https://github.com/dscape/clarinet
The parser is event-based, and since it’s streaming it makes dealing with huge files possible. The API is very close to sax and the code is forked from sax-js.
Disclaimer: I'm suggesting my own project.
I maintain a streaming JSON parser in Javascript which combines some of the features of SAX and DOM:
Oboe.js website
The idea is to allow streaming parsing, but not require the programmer to listen to lots of different events like with raw SAX. I like SAX but it tends to be quite low level for what most people need. You can listen for any interesting node from the JSON stream by registering JSONPath patterns.
The code is on Github here:
Oboe.js Github page
LitJSON supports a streaming-style API. Quoting from the manual:
"An alternative interface to handling JSON data that might be familiar to some developers is through classes that make it possible to read and write data in a stream-like fashion. These classes are JsonReader and JsonWriter.
"These two types are in fact the foundation of this library, and the JsonMapper type is built on top of them, so in a way, the developer can think of the reader and writer classes as the low-level programming interface for LitJSON."
If you are looking specifically for Python, then ijson claims to support it. However, it is only a parser, so I didn't come across anything for Python that can generate json as a stream.
For C++ there is rapidjson that claims to support both parsing and generation in a streaming manner.
Here's a NodeJS NPM library for parsing and handling streams of JSON:
https://npmjs.org/package/JSONStream
For Python, an alternative (apparently lighter and more efficient) to ijson is jsaone (see that link for rough benchmarks, showing that jsaone is approximately 3x faster).
DISCLAIMER: I'm the author of jsaone, and the tests I made are very basic... I'll be happy to be proven wrong!
Answering the question title: YAJL a JSON parser library in C:
YAJL remembers all state required to
support restarting parsing. This
allows parsing to occur incrementally
as data is read off a disk or network.
So I guess using yajl to parse JSON can be considered as processing stream of data.
In reply to your 2nd question, no, many languages have JSON parsers. PHP, Java, C, Ruby and many others. Just Google for the language of your choice plus "JSON parser".
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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.