Delete an item and all of it's attributes by primary key.
        You can perform a conditional delete by specifying an
        expected rule.

        :type table_name: str
        :param table_name: The name of the table containing the item.

        :type key: dict
        :param key: A Python version of the Key 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 delete_item(self, table_name, key,
                    expected=None, return_values=None,
                    object_hook=None):
        """
        Delete an item and all of it's attributes by primary key.
        You can perform a conditional delete by specifying an
        expected rule.

        :type table_name: str
        :param table_name: The name of the table containing the item.

        :type key: dict
        :param key: A Python version of the Key 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,
                'Key' : key}
        if expected:
            data['Expected'] = expected
        if return_values:
            data['ReturnValues'] = return_values
        json_input = json.dumps(data)
        return self.make_request('DeleteItem', json_input,
                                 object_hook=object_hook)