There are many ways of using ORDER BY descending in an SQLAlchemy but some of the important ways I am discussing here:-
You can import desc from the sqlalchemy package and use the function someselect.order_by() function it will do the task.
from sqlalchemy import desc someselect.order_by(desc(table1.mycol))
Another way you can do is to specify those things as column attributes. Like I am mentioning below. This way becomes handy when you see the relation definition type of things:-