Can we declare PonyORM models without using a database global variable?

Question

Declaring classes that map the db in ponyORM inherits from database as a global variable.

from pony.orm import *

db = Database()

class MyEntity(db.Entity):
    attr1 = Required(str)

Is there a way to declare Entities without relying on a global variable?

Maybe something in the line of

class MyEntity(get_db().Entity):

but with control over when the classes are declared so that get_db() returns the appropriate db.

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We have a few situations in which this would be desirable.

1. Mixing databases

Using multiple databases with Pony ORM

This is the solution we have currently running. But having inner Classes is ugly, specially because there are a lot of them.

Maybe we could make them go to the global space with global? or import the models within this inner function?

2. unit testing

Having a global variable causes errors in unit testing or makes it overly complicated because each setUp must check if the database is already bound, and ensure it is the right database.

3. mapping views

We would like to map views as pony classes. Declare some ORM classes, generate the tables, create the views, declare the ORM view classes.

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We took a look to other projects that also rely on global objects like flask or celery but we didn't find a solution that would apply to ponyORM.

Maybe it's just not possible and the database object has to be defined and that's it.