How to sign amazon web service requests from the python app engine?

Question

I use Amazon web service api from within my Google app engine application. Amazon have said that they will only accept signed requests from Aug 15, 2009. While they have given

Answer 1

Got this to work based on code sample at http://jjinux.blogspot.com/2009/06/python-amazon-product-advertising-api.html Here is a minor improved version that lets you merge a dict of call specific params with the basic params before making the call.

keyFile = open('accesskey.secret', 'r')
# I put my secret key file in .gitignore so that it doesn't show up publicly
AWS_SECRET_ACCESS_KEY = keyFile.read()
keyFile.close()

def amz_call(self, call_params):

    AWS_ACCESS_KEY_ID = ''
    AWS_ASSOCIATE_TAG = ''

    import time
    import urllib
    from boto.connection import AWSQueryConnection
    aws_conn = AWSQueryConnection(
        aws_access_key_id=AWS_ACCESS_KEY_ID,
        aws_secret_access_key=Amz.AWS_SECRET_ACCESS_KEY, is_secure=False,
        host='ecs.amazonaws.com')
    aws_conn.SignatureVersion = '2'
    base_params = dict(
        Service='AWSECommerceService',
        Version='2008-08-19',
        SignatureVersion=aws_conn.SignatureVersion,
        AWSAccessKeyId=AWS_ACCESS_KEY_ID,
        AssociateTag=AWS_ASSOCIATE_TAG,
        Timestamp=time.strftime("%Y-%m-%dT%H:%M:%S", time.gmtime()))
    params = dict(base_params, **call_params)
    verb = 'GET'
    path = '/onca/xml'
    qs, signature = aws_conn.get_signature(params, verb, path)
    qs = path + '?' + qs + '&Signature=' + urllib.quote(signature)
    print "verb:", verb, "qs:", qs
    return aws_conn._mexe(verb, qs, None, headers={})

Sample usage:

result = self.amz_call({'Operation' : 'ItemSearch' , 'Keywords' : searchString , 'SearchIndex' : 'Books' , 'ResponseGroup' : 'Small' })
if result.status == 200:
    responseBodyText = result.read()
    # do whatever ...