Where is ClosureTable?
I found the problem, seems ClosureTable does not get defined when using apsw_ext. I'll close this and refile if I find I can't use it from sqlite_ext.
See docs:

http://docs.peewee-orm.com/en/latest/peewee/playhouse.html?highlight=apsw#ClosureTable

ClosureTable is not defined. Using it produces an "is not defined" error.