Lookup books on Amazon's API.

aws.py

from django.conf import settings
from datetime import datetime
from urllib import urlencode
from httplib import HTTPConnection
from xml.dom.minidom import parse
import hmac, hashlib, base64

ACCESS_ID = getattr(settings, 'AWS')['ID']
ACCESS_SECRET = getattr(settings, 'AWS')['SECRET']

class AWSException(Exception):
    """ Abstract this to deal with AWS error callbacks from the API """
    pass

class ResponseNode(object):

    def __init__(self, node):
        self.node = node

    def __repr__(self):
        return "<%s %s>" % (self.__class__.__name__, self.node.nodeName)

    def __str__(self):
        if len(self.node.childNodes) == 1 and self.node.firstChild.nodeType == self.node.TEXT_NODE:
            return self.node.firstChild.data
        else:
            return self.node.nodeName

    def __getattr__(self, name):
        nodes = [ResponseNode(n) for n in self.node.childNodes if n.nodeName == name]
        if len(nodes) == 0:
            return None
        elif len(nodes) == 1:
            if str(nodes[0]) == name:
                return nodes[0]
            else:
                return str(nodes[0])
        else:
            return nodes

    def __len__(self):
        return len(self.node.childNodes)

    def __index__(self, i):
        return ResponseNode(self.node.childNodes[i])

    def __iter__(self):
        for node in self.node.childNodes:
            yield ResponseNode(node)

    def __contains__(self, name):
        if getattr(self, name) is not None:
            return True
        return False

    def __eq__(self, other):
        if str(self) == str(other):
            return True
        return False

    def children(self):
        return [n.nodeName for n in self.node.childNodes]

    def toxml(self):
        return self.node.toxml( )

    def toprettyxml(self):
        return self.node.toprettyxml( )

class ResponseParser(ResponseNode):
    """
    A factory class that returns Django objects from an AWS response XML.
    """

    def __init__(self, dom):
        super(ResponseParser, self).__init__(dom.documentElement)
        if str(self.Items.Request.IsValid) == "False":
            raise AWSException("Request Invalid")
        elif "Errors" in self.Items.Request:
            raise AWSException(self.Items.Request.Errors.Error.Message)

    def books(self):
        """ Constructs a dictionary of book attributes and returns them, temporary method for now """
        
        def findIsbn(obj):
            tags = ['EAN', 'EISBN', 'ISBN', 'ASIN']
            for t in tags:
                if getattr(obj, t, None) is not None:
                    return getattr(obj, t)
            raise AWSException('ISBN not found!')
        
        def findAuthors(obj):
            if 'Author' in obj:
                if isinstance(getattr(obj, 'Author'), (str, unicode)):
                    return getattr(obj, 'Author')
                else:
                    return ', '.join([str(a) for a in getattr(obj, 'Author')])
            raise AWSException('Author(s) not found!')

        if self.Items is not None:

            for item in self.Items:
                
                if item in ['Request', ]: continue

                """ For Simplicity, I'm just grabbing the vars I hope are there... we'll do it more generically later. """
                yield {
                    'isbn': findIsbn(item.ItemAttributes),
                    'title': item.ItemAttributes.Title,
                    'pubdate': item.ItemAttributes.PublicationDate,
                    'publisher': item.ItemAttributes.Publisher,
                    'pages': item.ItemAttributes.NumberOfPages,
                    'authors': findAuthors(item.ItemAttributes),
                    'coverURL': item.LargeImage.URL,
                    'binding': item.ItemAttributes.Binding,
                    'amazonUrl': item.DetailPageURL,
                }


class AWS(object):
    
    VERB = 'GET'
    HOST = 'ecs.amazonaws.com'
    URI = '/onca/xml'

    def __init__(self, **kwargs):
        
        self.Service = 'AWSECommerceService'
        self.Version = '2010-11-01'
        self.AWSAccessKeyId = ACCESS_ID
        self.Operation = None
        self.ResponseGroup = ','.join(['Images','ItemAttributes',])

        # Will add any additional parameters to query or override defaults:
        for (k,v) in kwargs.iteritems( ):
            setattr(self, k, v)

    @property
    def Timestamp(self):
        ts = datetime.utcnow( )
        return ts.strftime('%Y-%m-%dT%H:%M:%SZ')

    def _signParams(self, params):
        keys = params.keys( )
        keys.sort( ) # Sort in byte-order as required by the ECS API
        sortedQuery = urlencode([(k, params[k]) for k in keys]) 
        signature = '\n'.join([self.VERB, self.HOST, self.URI, sortedQuery])
        dig = hmac.new(ACCESS_SECRET, msg=signature, digestmod=hashlib.sha256).digest( )
        params['Signature'] = base64.b64encode(dig).decode( )
        return params

    def _requiredParams(self):
        params = { }
        # Add required parameters as stored in object:
        for (k,v) in self.__dict__.iteritems( ):
            params[k] = v
        # Add dynamic required parameters:
        params['Timestamp'] = self.Timestamp
        return params

    def _get(self, params):
        # Create parameters string:
        params.update(self._requiredParams( )) # Update with required params
        params = self._signParams(params) # Sign the parameters
        params = urlencode(params) # Urlencode the parameters
        
        # Create the HTTP Connection
        conn = HTTPConnection(self.HOST)
        conn.request(self.VERB, '?'.join([self.URI, params]))
        response = conn.getresponse( )
        data = parse(response)
        conn.close( )

        return data

    def itemLookup(self, isbn):
        self.Operation = 'ItemLookup'
        lookupParams = {'IdType':'ISBN', 'ItemId':isbn, 'SearchIndex':'Books'}
        try:
            return ResponseParser(self._get(lookupParams))
        except Exception as e:
            raise AWSException(str(e))

Hey, I'm quite new to python and django as a whole. Can you please explain how to use this? I'm interested in getting book info from ISBN.