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Automatically Scraping Webpages using Python 2.7

Written by SPK Blog Post
Published on July 17, 2013

In today’s Internet, it takes specific skills to efficiently find the “Data You Want” inside of the “Data You’re Given”. I was reminded of this the other day watching a colleague struggle through data collection, clicking buttons and getting diverted by advertisements that look like more buttons.

If you want specific data from a webpage, here’s a snippet of code that will do it for you using urllib and Regex. This was written to collect bulk data from the European Bioinformatics Institute (EBI) PDBePISA website; download the full, functional code as an attachment here. It was written to be executed using Python 2.7 — try the web app-based training at Codecademy.com if you’d like a great and easy crash-course on programming!

# The snippet of code below does not run; it is modified for

# readability. Download the attachment for the full code!

import urllib, urllib2, re

 

# …

 

for item in pdb_list:

    #

    #Build URL call, refer to URLLIB and URLLIB2 documentation”

    #

    url = “http://www.ebi.ac.uk/msd-srv/pisa/cgi-bin/piserver”

    values = { ‘page_key’ : ‘sform_page’,

              ‘action_key’ : ‘act_submit_pdb’,

              ‘dir_key’ : ‘632-4B-2AF’,

              ‘session_point’ : ‘2’,

              ‘radio_sf_session_type’ : ‘id_sf_dbsearch’,

              ‘radio_source’ : ‘id_pdbentry’,

              ‘entry0’ : item,

              ‘entry1’ : item,

              ‘edt_pdbcode’ : item }

    post = urllib.urlencode(values)

    request = urllib2.Request(url,post)

    response = urllib2.urlopen(request)

    html = response.read()

The above lines are used to build the POST request. Read about “HTML Forms” to get more background on this – this is how a website receives information from the text boxes when you click on the “Submit” button. Sometimes, you can leave all the values blank and just open a URL.

The result is a variable html that contains a long string of HTML code…

html = ‘\n<!doctype html>\n<!– paulirish.com/2008/conditional-stylesheets-vs-css-hacks-answer-neither/ –>\n<!–[if lt IE 7]> <html class=”no-js ie6 oldie” lang=”en”> <![endif]–>\n<!–[if IE 7]…

Next, I need to parse the string for the information I want. I use Regex for this:

    #

    #Use REGULAR EXPRESSION (REGEX) to find the text

    #and values that we want

    #

    search = re.findall(r‘Analysis: <strong><input style=”color:blue;bgcolor:white; border:0;” size=”64″ value=”(.*)” …’,html)

    if len(search)==1:

        analysis = search[0]

        print item +“:\tAnalysis:\t\t”+analysis

    else:

        analysis = “???”

        print item+“: \t*Error finding Analysis for “+item

 

I won’t go into the details of using RegEx, but you can read Regular-Expressions.info and download Kodos (Windows) to play with it. As an alternative, save the entire html string to a log file or check to see if a substring is inside the larger string.

Once you have the above working, you can really empower your computer to do your job for you:

  1. Run the program on a timer using Crontab or Windows Scheduled Tasks, have it “watch” a webpage for you.
  2. Use it to record information, such as license usage, for generating reports and graphs later.
  3. Alert yourself by email or SMS when a trigger appears on a target webpage.

Remember to download the attached batch_pisa_v2.py file to modify or run on your own. If you master this, I’m certain that you’ll be able to save yourself hours on a regular basis and, even more importantly, you’ll be able to provide creative solutions even after others have conceded defeat!

scraping

I’ve already told you that no problem in unsolvable – next, I’ll show you how to solve your problems faster.

Next Steps:

Edwin Chung
Client Program Manager, SPK & Associates

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