'Queue the deletion of an attribute from an item in DynamoDB.
This call will result in a UpdateItem request being issued
with update action of DELETE when the save method is called.
:type attr_name: str
:param attr_name: Name of the attribute you want to alter.
:type attr_value: set
:param attr_value: A set of values to be removed from the attribute.
This parameter is optional. If None, the whole attribute is
removed from the item.'

def delete_attribute(self, attr_name, attr_value=None):

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