REST API dependencies: are all of them needed?

[giovannipizzi]

There are quite a few dependencies in the rest extra. I'm not sure I understand, however, if they are all used and how. Maybe some of them are just "plugins" for flask and just need to be there, but could you:

• check if there are any dependencies that are not really needed, and remove them
• report here which one are used, how (i.e. if they are imported or used implicitly) and, especially in the latter case, what are they needed for?

Just to make two examples, if I do git grep marshmallow I don't get any hit in python files, but there are the dependencies flask-marshmallow==0.10.1 and marshmallow-sqlalchemy==0.19.0 - are they used?