<?php
 require('../AmazonApi.php');
 require_once ('../app/Mage.php');
 Mage::app();

 //Create API access object
 $public_key = '*************';
 $secret_key = '*************';
 $associate_tag = '**********-21';
 $amazon_api = new AmazonAPI($public_key, $secret_key, $associate_tag);


$products = Mage::getModel('catalog/product')
->getCollection()
->addAttributeToSelect('asin')
->addAttributeToSelect('description');

//Array of request parameters
foreach($products as $product)
{
$asin = $product->getAsin();
$product->setDescription($response);
$product->getResource()->saveAttribute($product, 'description');
$params_array = array(
'Operation' => 'ItemLookup',
'IdType' => 'ASIN',
'ItemId' => $asin ,
'ResponseGroup' => 'Tracks');

// returns a list of items for the search query 'Slow Magic'
$response = $amazon_api->sendRequest($params_array);

foreach ($response as $restponse)
{
sleep(1);
}

echo '<pre>';
print_r($response);
echo '</pre>';
}

foreach($parsed_xml->OperationRequest->Errors->Error as $error){
 echo "Error code: " . $error->Code . "rn";
 echo $error->Message . "rn";
 echo "rn";
 }

$product->setDescription($response);
$product->save();

$product->setDescription($response);
 $product->getResource()->saveAttribute($product, 'description')

$products = Mage::getModel('catalog/product')
->getCollection()
->addAttributeToSelect('asin')
->addAttributeToSelect('description')
->load($productId);

$products = Mage::getModel('catalog/product')
->getCollection()
->addAttributeToSelect('asin')
->addAttributeToSelect('description');