Create a new item or replace an old item with a new
        item (including all attributes).  If an item already
        exists in the specified table with the same primary
        key, the new item will completely replace the old item.
        You can perform a conditional put by specifying an
        expected rule.

        :type table_name: str
        :param table_name: The name of the table in which to put the item.

        :type item: dict
        :param item: A Python version of the Item data structure
            defined by DynamoDB.

        :type expected: dict
        :param expected: A Python version of the Expected
            data structure defined by DynamoDB.

        :type return_values: str
        :param return_values: Controls the return of attribute
            name-value pairs before then were changed.  Possible
            values are: None or 'ALL_OLD'. If 'ALL_OLD' is
            specified and the item is overwritten, the content
            of the old item is returned.

def put_item(self, table_name, item,
                 expected=None, return_values=None,
                 object_hook=None):
        """
        Create a new item or replace an old item with a new
        item (including all attributes).  If an item already
        exists in the specified table with the same primary
        key, the new item will completely replace the old item.
        You can perform a conditional put by specifying an
        expected rule.

        :type table_name: str
        :param table_name: The name of the table in which to put the item.

        :type item: dict
        :param item: A Python version of the Item data structure
            defined by DynamoDB.

        :type expected: dict
        :param expected: A Python version of the Expected
            data structure defined by DynamoDB.

        :type return_values: str
        :param return_values: Controls the return of attribute
            name-value pairs before then were changed.  Possible
            values are: None or 'ALL_OLD'. If 'ALL_OLD' is
            specified and the item is overwritten, the content
            of the old item is returned.
        """
        data = {'TableName' : table_name,
                'Item' : item}
        if expected:
            data['Expected'] = expected
        if return_values:
            data['ReturnValues'] = return_values
        json_input = json.dumps(data)
        return self.make_request('PutItem', json_input,
                                 object_hook=object_hook)