title: aws cli dynamo db (ValidationException) Error
body: <p>I'm looking to batch write item to dynamodb using python's boto3 module and i'm getting this. This is the first time i've ever worked with aws cli or boto3. The documentation says validation exception errors occur when there are empty values and possible incorrect data types, but i've played with all those and it doesn't seem to be working. </p>
  
  <p>Does dynamodb only like to have 25 items written to it at a time? how can i control those batches if so? </p>
  
  <p>My request:</p>
  
  <pre><code>client = boto3.client('dynamodb')
  response = client.batch_write_item(RequestItems=batch_dict)
  </code></pre>
  
  <p>Top of batch_dict:</p>
  
  <pre><code>{'scraper_exact_urls': [{'PutRequest': {'Item': {'Sku': {'S': 'T104P3'},
   'pps_id': {'N': '427285976'},
   'scraper_class_name': {'S': 'scraper_class_name'},
   'store_id': {'N': '1197386754'},
   'updated_by': {'S': 'user'},
   'updated_on': {'N': '1480714223'},
   'updated_url': {'S': 'http://www.blah.com'}}}},
   {'PutRequest': {'Item': {'Sku': {'S': 'T104P3'},
   'pps_id': {'N': '427285976'},
   'scraper_class_name': {'S': 'scraper_class_name'},
   'store_id': {'N': '1197386754'},
   'updated_by': {'S': 'user'},
   'updated_on': {'N': '1480714223'},
   'updated_url': {'S': 'http://www.blah.com'}}}},....
  </code></pre>
  
  <p>Schema:</p>
  
  <p>attributes:
             "pps_id"=>\Aws\DynamoDb\Enum\Type::NUMBER,
             "sku"=>\Aws\DynamoDb\Enum\Type::STRING,
             "scraper_class_name"=>\Aws\DynamoDb\Enum\Type::STRING,
             "store_id"=>\Aws\DynamoDb\Enum\Type::NUMBER,
             "updated_url"=>\Aws\DynamoDb\Enum\Type::STRING,
             "updated_by"=>\Aws\DynamoDb\Enum\Type::STRING,
             "updated_on"=>\Aws\DynamoDb\Enum\Type::NUMBER,
  fields:
  "pps_id",
             "scraper_class_name",</p>
  
  <p>The Error:</p>
  
  <pre><code>ClientError: An error occurred (ValidationException) when calling the    BatchWriteItem operation: 1 validation error detected: Value .... Map value   must satisfy constraint: [Member must have length less than or equal to 25,   Member must have length greater than or equal to 1]
  </code></pre>