basiccrawler 0.3.3
Basic web crawler that automates website exploration and producing web resource trees.
License: MIT license
Keywords: basiccrawler

BasicCrawler
============

Semi-automated crawling bot with special features for extracting website
structure automatically.

::

    from basiccrawler.crawler import BasicCrawler

    SOURCE_DOMAIN='http://learningequality.org'
    start_page = 'http://learningequality.org/kolibri/'

    class LECrawler(BasicCrawler):
        pass

    crawler = LECrawler(main_source_domain=SOURCE_DOMAIN,
                        start_page=start_page)

    web_resource_tree = crawler.crawl()

The crawler concludes will summary of the findings (according to crude
heuristics).

::

    # CRAWLER RECOMMENDATIONS BASED ON URLS ENCOUNTERED:
    ################################################################################
    1. These URLs are very common and look like global navigation links:
      -  http://learningequality.org/about/team/
      -  http://learningequality.org/about/board/
      -  http://learningequality.org/about/supporters/
      -  ...
    2. These are common path fragments found in URLs paths, so could correspond to site struture:
      -  ...
    ################################################################################

The web resource tree contains the information about the site structure
at a high level (``print_depth=3``) or in full detail
(``print_depth=100``). For example:

::

    crawler.print_tree(web_resource_tree, print_depth=4)

         - path: /kolibri/  (PageWebResource) 
           children:
            - path: /  (PageWebResource) 
              children:
               - path: /media/Rapport-Etude-Cameroun_KL_ENG.pdf  (MediaWebResource) 
            - path: /about/  (PageWebResource) 
              children:
               - path: /ka-lite/map/  (PageWebResource) 
            - path: /about/values/  (PageWebResource) 
            - path: /about/team/  (PageWebResource) 
            - path: /about/board/  (PageWebResource) 
            - path: /about/supporters/  (PageWebResource) 
            - path: /about/press/  (PageWebResource) 
            - path: /about/jobs/  (PageWebResource) 
            - path: /about/internships/  (PageWebResource) 
              children:
               - path: https://learningequality.org/about/jobs/?gh_jid=533166  (PageWebResource) 
            - path: /download/  (PageWebResource) 
            - path: /documentation/  (PageWebResource) 
            - path: /hardware_grant/  (PageWebResource) 
            - path: /ka-lite/  (PageWebResource) 
              children:
               - path: /ka-lite/infographic/  (PageWebResource) 
            - path: /translate/  (PageWebResource) 
            - path: https://blog.learningequality.org/?gi=2589e076ea04  (PageWebResource) 
            - path: /ka-lite/map/add/  (PageWebResource) 
            - path: /donate/  (PageWebResource) 
              children:
               - path: /static/doc/learning_equality_irs_determination_letter.pdf  (MediaWebResource) 
            - path: /cdn-cgi/l/email-protection  (PageWebResource) 

For this crawl, we didn’t find too many educational materials
(docs/videos/audio/webapps), but at least we get some idea of the links
on that page. Try it on another website.

Example usage
-------------

https://github.com/learningequality/sushi-chef-tessa/blob/master/tessa_cralwer.py#L229

TODO
----

-  Update examples + notebooks
-  path to url / vice versa (and possibly elsewhere): consider
   ``urllib.urlparse``? [e.g. ``url.startwith(source_domain)`` could be
   ``source_domain in url.domain`` to make it more flexible with
   subdomains

   -  Additional valid domains can be specified but ``url_to_path_list``
      assumes adding CHANNEL_ROOT_DOMAIN [we may wish to expand all
      links based on parent URL]
   -  refactor and remove need for MAIN_SOURCE_DOMAIN and use only
      SOURCE_DOMAINS instead

Future feature ideas
--------------------

-  Asynchronous download (not necessary but might be good for
   performance on large sites)

   -  don’t block for HTTP
   -  allow multiple workers getting from queue

-  content_selector hints for default ``on_page`` handler to follow
   links only within a certain subset of the HTML tree. Can have:

   -  site-wide selector at class level
   -  pass in additional ``content_selector`` from referring page via
      context dict

-  Automatically detect standard embed tags (audio, video, pdfs) and add
   links to web resource tree in default ``on_page`` handler.

Crawler API
-----------

The goal of the ``BasicCrawler`` class is to help with the initial
exploration of the source website. It is your responsibility to write a
subclass that uses the HTML, URL structure, and content to guide the
crawling and produce the web resource tree.

Your crawler should inherit from ``BasicCrawler`` and define:

1. What site we’re crawling and where to start:

   -  set the following attributes

      -  ``MAIN_SOURCE_DOMAIN`` e.g. ``'https://learningequality.org'``
         or pass as arg ``main_source_domain`` at creation time.
      -  ``START_PAGE`` e.g. ``'https://learningequality.org/'`` or pass
         at creation time as ``start_page``.

   -  ``IGNORE_URLS=[]``: crawler will ignore these URLs (can be
      specified as str, re, or callable)
   -  ``CRAWLING_STAGE_OUTPUT='chefdata/trees/web_resource_tree.json'``:
      where the output of the crawling will be stored

2. Run for the first time by calling ``crawler.crawl()`` or as a command
   line script

-  The BasicCrawler has logic for visiting pages and will print out on
   the a summary of the auto inferred site stricture findings and
   recommendations based on the URL structure observed during the
   initial crawl.
-  Based on the number of times a link appears on different pages of the
   site the crawler will suggest to you candidates for global navigation
   links. Most websites have an /about page, /contact us, and other such
   non-content-containing pages, which we do not want to include in the
   web resource tree. You should inspect these suggestions and decide
   which should be ignored (i.e. not crawled or included in the
   web_resource_tree output). To ignore URLs you can edit the
   attributes:

   -  ``IGNORE_URLS``: crawler will ignore these URLs Edit your crawler
      subclass’ code and append to ``IGNORE_URLS`` the URLs you want to
      skip (anything that is not likely to contain content).

3. Run the crawler again, this time there should be less noise in the
   output.

-  Note the suggestion for different paths that you might want to handle
   specially (e.g. ``/course``, ``/lesson``, ``/content``, etc.) You can
   define class methods to handle each of these URL types:

   ::

        def on_course(self, url, page, context):
            # what do you want the crawler to do when it visits the  course with `url`
            # in the `context` (used for extra metadata; contains reference to parent)
            # The BeautifulSoup parsed contents of the `url` are provided as `page`.

        def on_lesson(self, url, page, context):
            # what do you want the crawler to do when it visits the lesson

        def on_content(self, url, page, context):
            # what do you want the crawler to do when it visits the content url

Check out the default ``on_page`` method so see how a web resource tree
is constructed:
https://github.com/learningequality/BasicCrawler/blob/master/basiccrawler/crawler.py#L212