'Queue the addition of an attribute to an item in DynamoDB.
This will eventually result in an UpdateItem request being issued
with an update action of ADD when the save method is called.
:type attr_name: str
:param attr_name: Name of the attribute you want to alter.
:type attr_value: int|long|float|set
:param attr_value: Value which is to be added to the attribute.'

def add_attribute(self, attr_name, attr_value):

    self._updates[attr_name] = ('ADD', attr_value)
