Extract basic info from HTML webpages.

## Project description

==========
Extraction
==========

Extraction is a Python package for extracting titles, descriptions,
images and canonical urls from web pages. You might want to use Extraction
if you're building a link aggregator where users submit links and you
want to display them (like submitting a link to Facebook, Digg or Delicious).

Extraction is not a web crawling or content retrieval mechanism, rather
it is a tool to use on data which has always been retrieved or crawled
by a different tool.

Developed against Python 2.7, but should also work with Python 2.6+ if
you install the importlib requirement.

Hello World Usage
=================

An extremely simple example of using extraction is::

>>> import extraction
>>> import requests
>>> url = "http://lethain.com/social-hierarchies-in-engineering-organizations/"
>>> html = requests.get(url).text
>>> extracted = extraction.Extractor().extract(html, source_url=url)
>>> extracted.title
>>> "Social Hierarchies in Engineering Organizations - Irrational Exuberance"
>>> print extracted.title, extracted.description, extracted.image, extracted.url

Note that source_url is optional in extract, but is recommended
as it makes it possible to rewrite relative urls and image urls
into absolute paths. source_url is not used for fetching data,
but can be used for targetting extraction techniques to the correct
domain.

extraction mechanisms, are beneath the installation section.

Installation
============

The simplest way to install Extraction is via PyPi::

pip install extraction

If you want to develop against extraction, you can install from GitHub::

git clone
cd extraction
virtualenv env
. ./env/bin/activate
pip install -r requirements.txt
python setup.py develop

Then you can run the tests::

python tests/tests.py

All of which should pass in a sane installation.

Extraction Techniques
=====================

This section lists the current techniques used by extraction.
To rerank the techniques, remove techniques or add new techniques
of your own, look at the Using Extraction section below.

------------------------------

Every webpage's head tag contains has a title tag, and many also
This technique parses data that looks like::

<meta name="description" content="Will Larson&#39;s blog about programming and other things." />
<title>Digg v4&#39;s Architecture and Development Processes - Irrational Exuberance</title>

While the head tag is authoritative source of canonical URLs and RSS,
it's often very hit or miss for titles, descriptions and such.
At worst, it's better than nothing.

-------------------------------------------

For better or for worse, the highest quality source of page data is usually
the Facebook Opengraph meta tags <https://developers.facebook.com/docs/opengraphprotocol/>.
This technique uses Opengraph tags, which look like this::

...
<meta property="og:title" content="Something"/>
<meta property="og:url" content="http://www.example.org/something//"/>
<meta property="og:image" content="http://images.example.org/a/"/>
<meta property="og:description" content="Something amazing."/>
...

as their source of data.

extraction.techniques.HTML5SemanticTags
---------------------------------------

The HTML5 article tag, and also the video tag give us some useful
hints for extracting page information for the sites which happen to
utilize these tags.

This technique will extract information from pages formed like::

<html>
<body>
<h1>This is not a title to HTML5SemanticTags</h1>
<article>
<h1>This is a title</h1>
<p>This is a description.</p>
<p>This is not a description.</p>
</article>
<video>
<source src="this_is_a_video.mp4">
</video>
</body>
</html>

Note that HTML5SemanticTags is intentionally much more conservative than
SemanticTags, as it provides high quality information in the small number
of cases where it hits, and otherwise expects SemanticTags to run sweep
behind it for the lower quality, more abundant hits it discovers.

extraction.techniques.SemanticTags
----------------------------------

This technique relies on the basic tags themselves--for example,
all img tags include images, most h1 and h2 tags include titles,
and p tags often include text usable as descriptions::

<html>
<body>
<h1>This will be extracted as a title.</h1>
<h2>So will this, but after all H1s.</h2>
<img src="this_will_be_extracted_as_an_img.png">
<p>And this as a description.</p>
<p>This as another possible description.</p>
<p>This as a third possible description.</p>
</body>
</html>

There is a limit, defined within SemanticTags of how many
tags of a given type will be consumed, and is usually 3-5,
with the exception of images, where it is 10 (as this is
actually a valid way to detect images, unlike the others).

This is a true last resort technique.

Using Extraction
================

This section covers various ways to use extraction, both using

For more examples, please look in the extraction/examples
directory.

Basic Usage
-----------

The simplest possible example is the "Hello World" example from above::

>>> import extraction
>>> import requests
>>> url = "http://lethain.com/social-hierarchies-in-engineering-organizations/"
>>> html = requests.get(url).text
>>> extracted = extraction.Extractor().extract(html, source_url=url)
>>> extracted.title
>>> "Social Hierarchies in Engineering Organizations - Irrational Exuberance"
>>> print extracted.title, extracted.description, extracted.image, extracted.url

Using Custom Techniques and Changing Technique Ordering
-------------------------------------------------------

The order techniques are run in is significant, and the most accurate
techniques should always run first, and more general, lower quality
techniques later on.

This is because titles, descriptions, images and urls are stored
internally in a list, which is built up as techniques are run,
and the title, url, image and description properties
simply return the first item from the corresponding list.

Techniques are represented by a string with the full path to the
technique, including its class. For example "extraction.technique.FacebookOpengraphTags"
is a valid representation of a technique.

The default ordering of techniques is within the extraction.Extractor's
techniques class variable, and is::

extraction.techniques.HTML5SemanticTags
extraction.techniques.SemanticTags

You can modify the order and inclusion of techniques in three ways.
First, you can modify it by passing in a list of techniques to the
optional techniques parameter when initializing an extraction.Extractor::

>>> extractor = extraction.Extractor(techniques=techniques)

The second approach is to subclass Extractor with a different value of techniques::

from extraction import Extractor

class MyExtractor(Extractor):
techniques = ["my_module.MyTechnique"]

Finally, the third option is to directly modify the techniques class variable.
This is probably the most unpredictable technique, as it's possible for mutiple
pieces of code to perform this modification and to create havoc, if possible
use one of the previous two techniques to avoid future debugging::

>>> import extraction
>>> extraction.Extractor.techniques.insert(0, "my_module.MyAwesomeTechnique")
>>> extraction.Extractor.techniques.append("my_module.MyLastReportTechnique")

Again, please try the first two techniques instead if you value sanity.

Writing New Technique
---------------------

It may be that you're frequently parsing a given website and
aren't impressed with how the default extraction techniques are
performing. In that case, consider writng your own technique.

Let's take for example a blog entry at lethain.com <http://lethain.com/social-hierarchies-in-engineering-organizations/>,
which uses the H1 tag to represent the overall blogs title,
and always uses the first H2 tag in DIV.page for its actual
title.

A technique to properly extract this data would look like::

from extraction.techniques import Technique
from bs4 import BeautifulSoup
class LethainComTechnique(Technique):
def extract(self, html):
"Extract data from lethain.com."
soup = BeautifulSoup(html)
page_div = soup.find('div', class_='page')
text_div = soup.find('div', class_='text')
return { 'titles': [page_div.find('h2').string],
'dates': [page_div.find('span', class_='date').string],
'descriptions': [" ".join(text_div.find('p').strings)],
'tags': [x.find('a').string for x in page_div.find_all('span', class_='tag')],
'images': [x.attrs['src'] for x in text_div.find_all('img')],
}

To integrate your technique, take a look at the Using Custom Techniques and Changing Technique Ordering
section above.

Adding new techniques incorporating microformats is an interesting
area for some consideration. Most microformats have very limited
usage, but where they are in use they tend to be high quality sources
of information.

Subclassing Extracted to Extract New Types of Data
--------------------------------------------------

Your techniques can return non-standard keys in the dictionary
returned by extract, which will be available in the Extracted()._unexpected_values
dictionary. In this way you could fairly easily add support for extracting

For a contrived example, we'll extract my address from willarson.com <http://willarson.com/>,
which is in no way a realistic example of extracting an address, and is
only meant as an example of how to add a new type of extracted data.

As such, to add support for extracting address should look like (a fuller,
commented version of this example is available in extraction/examples/new_return_type.py,
I've written this as concisely as possible to fit into this doc more cleanly)::

from extraction.techniques import Technique
from extraction import Extractor, Extracted
from bs4 import BeautifulSoup

@property

"Extractor which supports addresses as first-class data."

def extract(self, html):
soup = BeautifulSoup(html)

Usage would then look like::

>>> import requests
>>> extracted = extractor.extract(requests.get("http://willarson.com/"))
"Cole Valey San Francisco, CA USA"

There you have it, extracted addresses as first class extracted data.

Passing Parameters to Techniques
--------------------------------

There isn't a mechanism for passing parameters to Techniques
when they are initialized, but it is possible to customize
the behavior of Techniques in a couple of ways.

First, you can simply subclass the Technique with the specific
behavior you want, perhaps pulling the data from Django settings
or what not.

class MyTechnique(Technique):
def __init__(self, *args, **kwargs):
if 'something' in kwargs:
self.something = kwargs['something']
del kwargs['something']
else:
self.something = "something else"
return super(MyTechnique, self).__init__(*args, **kwargs)

def extract(html, source_url=None):
print self.something
return super(MyTechnique, self).extract(html, source_url=source_url)

Second, all techniques are passed in the Extractor being used
to process them, so you can bake the customization into an
extraction.Extractor subclass::

from extraction import Extractor
from extraction.techniques import Technique

class MyExtractor(Extractor):
techniques = ["my_module.MyTechnique"]
def __init__(self, something, *args, **kwargs):
self.something = something
super(MyExtractor, self).__init__(*args, **kwargs)

class MyTechnique(Technique):
class extract(self, html, source_url=None):
print self.extractor.something
return super(MyTechnique, self).extract(html, source_url=source_url)

Between these two techniques, it should be feasible to get the
customization of behavior you need.

Implementation Details
======================

I've tried to comment the classes and modules themselves in a fairly
indepth fashion, and would recommend reading them for the most details,

extraction/tests.py
extraction/__init__.py
extraction/techniques.py

Hopefully all questions are answered therein.

Contributions, Questions, Concerns
==================================

Please open a GitHub pull-request with any improvements,
preferably with tests, and I'll be glad to merge it in.

## Project details

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