In the first part of this series, you see how ruby and python retrieve data from given URL and then parse the results using regular expression. In part two, the code is extended to query prices from Amazon through Amazon Web Services.

1. Specify executable
   Ruby

   #!/usr/bin/ruby

   Python

   #!/usr/bin/python

2. Import modules
   Ruby

   require ’net/http’
   require ’rexml/document’

   Python

   import sys
   import re
   import urllib
   from xml.dom.ext.reader import Sax2
   from xml.dom.ext import Print
   from xml import xpath

3. Validate argument
   Ruby

   if ARGV.length == 0
     puts "#{$0}: You must enter at least one argument"
     exit
   end

   Python

   if len(sys.argv) == 1:
       print "%s: You must enter at least one argument." % sys.argv[0]
       sys.exit()

4. Initialize output and regular expressions
   Ruby

   output = ""
    
   not_in_collection_re = /class="yourEntryWouldBeHereData"/ix
   on_shelf_re = /CHECK SHELF/ix
   checked_out_re = /DUE /ix

   Python

   output = ’’
    
   not_in_collection_re = re.compile(r’class="yourEntryWouldBeHereData"’,re.I)
   on_shelf_re = re.compile(r’CHECK SHELF’,re.I)
   checked_out_re = re.compile(r’DUE ’,re.I)

5. Start loop
   Ruby

   ARGV.each do |isbn|

   Python

   for isbn in sys.argv[1:]:

6. Validate input
   Ruby

     if not isbn.match(/[0-9xX]{10}/)
       output << "ISBN #{isbn} is invalid.\n"
       next
     end
    
     output << "ISBN: #{isbn}\n"

   Python

       if not re.match(r’[0-9xX]{10}’,isbn):
           output += ’ISBN %s is invalid.\n’ % isbn
           continue
    
       output += ’ISBN: %s\n’ % isbn

7. Query AWS
   Ruby

     amazon_params = {’Service’ => ’AWSECommerceService’,
                      ’Operation’ => ’ItemLookup’,
                      ’AWSAccessKeyId’ => ’XXXXXXXXXXXXXXXXXXX’,
                      ’ItemId’ => isbn,
                      ’ResponseGroup’ => ’Medium,OfferFull’,
                      ’MerchantId’ => ’All’}.map{|key,value|"#{key}=#{value}"}.join("&")
    
     amazon_response = Net::HTTP.get_response(’webservices.amazon.com’,
                                              ’/onca/xml?’ << amazon_params)

   Python

       amazon_params = {
           ’Service’: ’AWSECommerceService’,
           ’Operation’: ’ItemLookup’,
           ’AWSAccessKeyId’: ’XXXXXXXXXXXXXXXXXXX’,
           ’ItemId’: isbn,
           ’ResponseGroup’: ’Medium,OfferFull’,
           ’MerchantId’: ’All’,
       }
    
       amazon_response = urllib.urlopen(’http://webservices.amazon.com/onca/xml’,urllib.urlencode(amazon_params))

8. Parse XML
   Ruby

     xml = REXML::Document.new(amazon_response.body)

   Python

       xml = Sax2.FromXmlStream(amazon_response).documentElement

9. Extract information from the XML
   Ruby

     new_price = xml.root.elements["Items/Item/OfferSummary/LowestNewPrice/FormattedPrice"]
     if new_price.nil?
       output << "\tNew: None available\n"
     else
       output << "\tNew: #{new_price.text}\n"
     end
    
     used_price = xml.root.elements["Items/Item/OfferSummary/LowestUsedPrice/FormattedPrice"]
     if used_price.nil?
       output << "\tUsed: None available\n"
     else
       output << "\tUsed: #{used_price.text}\n"
     end
    
     collectible_price = xml.root.elements["Items/Item/OfferSummary/LowestCollectiblePrice/FormattedPrice"]
     if collectible_price.nil?
       output << "\tCollectible: None available\n"
     else
       output << "\tCollectible: #{collectible_price.text}\n"
     end

   Python

       try:
           new_price = xpath.Evaluate(’Items/Item/OfferSummary/LowestNewPrice/FormattedPrice’,xml)[0]
           output += ’\tNew: %s\n’ % new_price.childNodes[0].nodeValue
       except:
           output += ’\tNew: None\n’
    
       try:
           used_price = xpath.Evaluate(’Items/Item/OfferSummary/LowestUsedPrice/FormattedPrice’,xml)[0]
           output += ’\tUsed: %s\n’ % used_price.childNodes[0].nodeValue
       except:
           output += ’\tUsed: None\n’
    
       try:
           collectible_price = xpath.Evaluate(’Items/Item/OfferSummary/LowestCollectiblePrice/FormattedPrice’,xml)[0]
           output += ’\tCollectible: %s\n’ % collectible_price.childNodes[0].nodeValue
       except:
           output += ’\tCollectible: None\n’

10. Query Skokie
    Ruby

      response = Net::HTTP.get_response(’catalog.skokielibrary.info’,
                                        "/search~S4/i?SEARCH=#{isbn}")

    Python

        response = urllib.urlopen(’http://catalog.skokielibrary.info/search~S4/i’,’SEARCH=%s’ % isbn)
        body = response.read()

11. Parse the result
    Ruby

      if not_in_collection_re.match(response.body)
        output << "ISBN #{isbn} is not in the Skokie collection.\n"
      elsif on_shelf_re.match(response.body)
        output << "ISBN #{isbn} is on the shelf.\n"
      elsif checked_out_re.match(response.body)
        output << "ISBN #{isbn} is currently checked out.\n"
      else
        output << "ISBN #{isbn} response: Unparseable!.\n"
      end

    Python

        if not_in_collection_re.search(body):
            output += ’ISBN %s is not in the Skokie collection.\n’ % isbn
        elif on_shelf_re.search(body):
            output += ’ISBN %s is on the shelf.\n’ % isbn
        elif checked_out_re.search(body):
            output += ’ISBN %s is currently checked out.\n’ % isbn
        else:
            output += ’ISBN %s response: Unparseable!\n’ % isbn

12. End loop
    Ruby

    end

    Python

13. Print output
    Ruby

    puts output

    Python

    print output

Not too bad! Python can do what Ruby do but slightly longer due to too simple syntax, especially, XML APIs. Ruby comes with rexml while Python has pyxml as an external package. So choosing Ruby and Python cannot be done based on just syntax or features. It is up to you. Do you like short and compact code? Do you like clean and clear code?

Don't forget to read part 1, 2, 3.

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