I need to parse a bunch of random pages and add them to a DB. I am thinking of using regular expressions but I was wondering if there are any 'special' techniques (other than looking for content between known text/tags). The content is more(not always) like:
Some Title
Text related to Title
I guess I don't need to extract complete Text but some way to know where the Title/Paragraph and extract the content from there. The content itself may have images/links that I would like to retain.
Thanks!
Please see this answer: RegEx match open tags except XHTML self-contained tags
Use Python. http://www.python.org/
Use Beautiful Soup. http://www.crummy.com/software/BeautifulSoup/
You need to use a proper HTML parser, and extract the elements you’re interested in via the parser’s API (or via the DOM).
Since I don’t know what language you’re programming in, it’s rather difficult to recommend a parser, but some well known ones are Jericho for Java, and Beautiful Soup for Python.
Related
I have a project where my input files used to be XML. I'm now being asked to start processing HTML with embedded CSS instead, and I'd like to accomplish this as cleanly and with as few code changes as possible. I was using XML::LibXML to parse the XML files, but now that we're moving to HTML with CSS, I'm thinking I'll need to move to something else. That said, before I dig myself knee deep into silly decisions I'll likely regret, I wanted to ask here: what do you guys use for this kind of task?
The structures of the old XML and the new HTML input files are pretty similar, with both holding the same information. The HTML uses divs in place of the XML's text nodes, and holds its style information in style tags and attributes instead of separated xml attributes.
An example of the old XML is:
<text font="TimesNewRoman,BoldItalic" size="11.04" x="59" y="405" w="52"
h="12" bold="yes" italic="yes" cs="4.6" o_bbox="59,405;52,12"
o_size="11.04" o_cs="4.6">
Some text
</text>
An example of the new HTML is:
<div o="9ka" style="position:absolute;top:145;left:89;x-pdf-top:744;x-pdf-left:60;x-pdf-bottom:732;x-pdf-right:536;">
<span class="ft19" >
Some text
</span></nobr>
</div>
where "ft19" refers to a css style element from the top of the page of the format:
.ft19{ vertical-align:top;font-size:14px;x-pdf-font-size:14px;
font-family:Times;color:#000000;x-pdf-color:#000000;font-style:italic;
x-pdf-letter-spacing:0.83px;}
Basically, all I want is a parser that can read the stylistic elements of each node as attributes, so I could do something like:
my #texts_arr = $page_node->findnodes('text');
my $test_node = $texts_arr[1];
print "node\'s bold value is: " . $text_node->getAttribute('bold');
as I'm able to do with the XML. Does anything like that exist for parsing HTML? I'd really like to make sure I start this the right way instead of finding something that sort of does what I want on CPAN and realizing two months later that there was another module that was way better for what I'm trying to do.
Ideas?
The basic one I am aware of is HTML::Parser.
There is also a project that works with it, Marpa::HTML which is the work of the larger parser project Marpa, which parses any language that can be described in BNF, documented on the author's blog which is very interesting but much newer and experimental.
I also see that wildly successful WWW::Mechanize uses HTML::TokeParser, and it uses HTML::PullParser, so there's that too.
If you need something even more generic (and evil) you can look into "writing" your own using something like Text::Balanced (which has some nice methods for tags, not sure about tag properties though) or even Regexp::Grammars, but again this means reinventing the wheel somewhat, I would only choose these routes if the above don't do what you need.
Perhaps I haven't helped. Perhaps I have just done a literature search for you, but maybe one of these will work better for you than others.
Edit: one more parser for you, seems like it might do what you need HTML::Tree. Then look at methods like look_down from HTML::Element to act on the tree. I saw an example here.
It's not clear - is the Perl parsing for the purposes of doing the conversion to HTML (with embedded CSS)? If so, why not forget Perl and use XSLT which is designed to transform XML documents?
I would like to parse a html page and extract the meaningful text from it. Anyone knows some good algorithms to do this?
I develop my applications on Rails, but I think ruby is a bit slow in this, so I think if exists some good library in c for this it would be appropriate.
Thanks!!
PD: Please do not recommend anything with java
UPDATE:
I found this link text
Sadly, is in python
Use Nokogiri, which is fast and written in C, for Ruby.
(Using regexp to parse recursive expressions like HTML is notoriously difficult and error prone and I would not go down that path. I only mention this in the answer as this issue seems to crop up again and again.)
With a real parser like for instance Nokogiri mentioned above, you also get the added benefit that the structure and logic of the HTML document is preserved, and sometimes you really need those clues.
Solutions integrating with Ruby
use Nokogiri as recommended by Amigable Clark kant
Use Hpricot
External Solutions
If your HTML is well-formed, you could use the Expat XML Parser for this.
For something more targeted toward HTML-only, the W3C actually released the code for the LibWWW, which contains a simple HTML parser (documentation).
Lynx is able to do this. This is open source if you want to take a look at it.
You should strip all angle-bracketed part from text and then collapse white-spaces.
In theory the < and > should not be there in other cases. Pages contain < and > everywhere instead of them.
Collapsing whitespaces: Convert all TAB, newline, etc to spaces, then replace every sequence of spaces to a single space.
UPDATE: And you should start after finding the <body> tag.
From time to time, I see web pages whose content is solely written in XML (not HTML or XHTML). These pages usually have some style sheets (either XSLT or CSS) attached to them which makes them look like any other ordinary web page.
My question is, what are the advantages of such an approach (if any), and why would anyone choose to work this way?
EDIT: If this is a good thing, why is it not widespread?
EDIT 2: Thanks everyone for the great responses. They really enlightened me. I also found this question whose content is also related.
It's easier to generate it programmatically and reuse it for other purposes than displaying as webpage.
Update:
EDIT: If this is a good thing, why is it not widespread?
Not everyone needs to generate it programmatically or reuse it for other purposes than displaying as webpage. It's then easier to use plain HTML.
One possible advantage would be for use of the data of the page in something other than a web browser; that would (presumably) be easier to do if a page's content were well-formed XML. Of course in theory a well-formed, semantic XHTML page should be nearly as able to be parsed, as well.
It can also be easier to generate XML instead of XHTML, depending on the data source.
When you are getting XML data in to your system, and you are supposed to present this XML data then it is much easier to write some XSLT for that XML instead of parsing it using some sort of parser and then presenting the data.
That can be a valid point for using XML instead of XHTML or HTML
Update
To answer your question on why this is not widespread, is because XSTL is tedious and hard to work with. Specifically XPath, which can be for some people quite difficult to use.
Those pages use XSLT to get rendered on the client side. Not every browser (especially older ones) supports rendering XML + XSLT. XML can however be used server-side as template and get transformed to HTML by the application running on the server. I personally don't see any advantages to this approach.
There are a lot more web pages that are written solely in XML than you know. You're only seeing the ones that do the XSLT transformation on the client side. Server-side transformation of XML is not at all unusual, because there's a plethora of things that produce data in XML, and transforming XML to HTML in XSLT is straightforward. You'll never know this is happening if you just look at the HTML, which bears no signs of having been generated via XSLT.
Personally, I don't understand it either though one of the biggest problems is support in IE. I created a skeleton ecommerce site serving XML, transformed by XSLT and styled using CSS. I sorely missed the ability to use XLink and other wonderful XML features. It's also nice to be able to tag the data for what it is. I used a 'menu' tag for the restaurant menus. 'price' tags for prices and so on. If a user clicked on a link to change menus, all I had to do was send the name of the item, the price and the description instead of the complete page. iirc, a 4K or more HTML menu page was only 200 bytes of sent data.
As far as the "one error makes everything crash in XML" type comments, the same is true of any programming language so proper coding should be no bother for programmers and careful HTML/CSS types.
Before anyone says that what I did was actually XHTML...no. I served XML. I did call up XHTML namespaces when needed for links, images and HTML type things but only when necessary.
I have some html (in this case created via TinyMCE) that I would like to add to a page. However, for security reason, I don't want to just print everything the user has entered.
Does anyone know of a templatetag (a filter, preferably) that will allow only a safe subset of html to be rendered?
I realize that markdown and others do this. However, they also add additional markup syntax which could be confusing for my users, since they are using a rich text editor that doesn't know about markdown.
There's removetags, but it's a blacklisting approach which fails to remove tags when they don't look exactly like the well-formed tags Django expects, and of course since it doesn't attempt to remove attributes it is totally vulnerable to the 1,000 other ways of script-injection that don't involve the <script> tag. It's a trap, offering the illusion of safety whilst actually providing no real security at all.
HTML-sanitisation approaches based on regex hacking are almost inevitably a total fail. Using a real HTML parser to get an object model for the submitted content, then filtering and re-serialising in a known-good format, is generally the most reliable approach.
If your rich text editor outputs XHTML it's easy, just use minidom or etree to parse the document then walk over it removing all but known-good elements and attributes and finally convert back to safe XML. If, on the other hand, it spits out HTML, or allows the user to input raw HTML, you may need to use something like BeautifulSoup on it. See this question for some discussion.
Filtering HTML is a large and complicated topic, which is why many people prefer the text-with-restrictive-markup languages.
Use HTML Purifier, html5lib, or another library that is built to do HTML sanitization.
You can use removetags to specify list of tags to be remove:
{{ data|removetags:"script" }}
I have to parse a series of web pages in order to import data into an application. Each type of web page provides the same kind of data. The problem is that the HTML of each page is different, so the location of the data varies. Another problem is that the HTML code is poorly formatted, making it impossible to use a XML-like parser.
So far, the best strategy I can think of, is to define a template for each kind of page, like:
Template A:
<html>
...
<tr><td>Table column that is missing a td
<td> Another table column</td></tr>
<tr><td>$data_item_1$</td>
...
</html>
Template B:
<html>
...
<ul><li>Yet another poorly formatted page <li>$data_item_1$</td></tr>
...
</html>
This way I would only need one single parser for all the pages, that would compare each page with its template and retrieving the $data_item_1$, $data_item_2$, etc. Still, it is going to be a lot of work. Can you think of any simpler solution? Any library that can help?
Thanks
You can pass the page's source through tidy to get a valid page. You can find tidy here
. Tidy has bindings for a lot of programming languages. After you've done this, you can use your favorite parser/content extraction technique.
I'd recommend Html Agility Pack. It has the ability to work with poorly structured HTML while giving you Xml like selection using Xpath. You would still have to template items or select using different selections and analyze but it will get you past the poor structure hump.
As mentioned here and on other SO answers before, Beautiful Soup can parse weird HTML.
Beautiful Soup is a Python HTML/XML parser designed for quick turnaround projects like screen-scraping. Three features make it powerful:
Beautiful Soup won't choke if you give it bad markup. It yields a parse tree that makes approximately as much sense as your original document. This is usually good enough to collect the data you need and run away.
Beautiful Soup provides a few simple methods and Pythonic idioms for navigating, searching, and modifying a parse tree: a toolkit for dissecting a document and extracting what you need. You don't have to create a custom parser for each application.
Beautiful Soup automatically converts incoming documents to Unicode and outgoing documents to UTF-8. You don't have to think about encodings, unless the document doesn't specify an encoding and Beautiful Soup can't autodetect one. Then you just have to specify the original encoding.
Beautiful Soup parses anything you give it, and does the tree traversal stuff for you. You can tell it "Find all the links", or "Find all the links of class externalLink", or "Find all the links whose urls match "foo.com", or "Find the table heading that's got bold text, then give me that text."
Use HTML5 parser like html5lib.
Unlike HTML Tidy, this will give you error handling very close to what browsers do.
There's a couple C# specific threads on this, like Looking for C# HTML parser.
Depending on what data you need to extract regular expressions might be an option. I know a lot of people will shudder at the thought of using RegExes on structured data but the plain fact is (as you have discovered) that a lot of HTML isn't actually well structured and can be very hard to parse.
I had a similar problem to you, but in my case I only wanted one specific piece of data from the page which was easy to identify without parsing the HTML so a RegEx worked very nicely.