Python __call__ special method practical example

Question

I know that __call__ method in a class is triggered when the instance of a class is called. However, I have no idea when I can use this special method, because

Answer 1

I just stumbled upon a usage of __call__() in concert with __getattr__() which I think is beautiful. It allows you to hide multiple levels of a JSON/HTTP/(however_serialized) API inside an object.

The __getattr__() part takes care of iteratively returning a modified instance of the same class, filling in one more attribute at a time. Then, after all information has been exhausted, __call__() takes over with whatever arguments you passed in.

Using this model, you can for example make a call like api.v2.volumes.ssd.update(size=20), which ends up in a PUT request to https://some.tld/api/v2/volumes/ssd/update.

The particular code is a block storage driver for a certain volume backend in OpenStack, you can check it out here: https://github.com/openstack/cinder/blob/master/cinder/volume/drivers/nexenta/jsonrpc.py

EDIT: Updated the link to point to master revision.