gistfile1.py

def ascii_sorting(l)
 
    convert = lambda text: int(text) if text.isdigit() else text
    ascii_key = lambda key: [ convert(c) for c in re.split('([0-9]+)', key) ]
    return sorted(l, key=ascii_key )

def aws_request(operation="ItemSearch"):

 
	conf = ConfigParser.ConfigParser()
	conf.read('aws_api.conf')
	base_url = conf.get('aws_api', 'url')
	access_key= conf.get('aws_api', 'access_key')
	secret_key= conf.get('aws_api', 'secret_key')
			
	url_params = {'Operation':operation,'Service':"AWSECommerceService",
	'AWSAccessKeyId':access_key,'Version':"2009-10-01",'ItemPage':"1",'Keywords':"Amazon"}
    
    #add the timestamp
	url_params['Timestamp'] = time.strftime("%Y-%m-%dT%H:%M:%S", time.gmtime())
	# encode the url params
	values = map(lambda x:urllib.quote(x,safe='~'),url_params.values())
	keys =map(lambda x:urllib.quote(x,safe='~'),url_params.keys())
	#sort in ASCII order
	keys = ascii_sorting(keys)
	values = map(url_params.get, keys)
	# Reconstruct the URL paramters and encode them
	url_string = urllib.urlencode( zip(keys,values) )
				 
	#String to sign
	string_to_sign = """GET
	ecs.amazonaws.com
	/onca/xml
	%s""" % url_string	 

	# Sign the request
	signature = hmac.new(secret_key,string_to_sign,hashlib.sha256).digest()
	signature = base64.encodestring(signature)
	# Encode url safe the signature
	signature = urllib.quote(signature ,safe='~')
	print "%s?%s&Signature=%s" % (base_url,url_string, signature)