Ticket:Projection Doubt

What countries do we have to specify? If a array, then how do we use $in in python? It shows Invalid syntax.
So confusing! MongoDB always confuses students a lot

Valid syntax: {"field": {"$in": ["abc", "xyz"]}} but if you are doing in db.py
Its should be like this: {"countries": {"$in": countries}}
because countries it self is an array, see test_projection.py

It may be obvious for professional python developers, but for me it took quite a time to figure it out. While the $in operator does work in python shell (javascript) and Compass, I got an invalid syntax error in pyhton (file db.py). The solution is to put the $in operator into quotation marks ("$in"), so maybe in the next course the original db.py file could be more helpful regarding this python related challenge?