Datatypes for python

[adsharma]

Looking for reviewers for this pull request:

py2many/py2many#443

More context:

https://github.com/adsharma/adt/blob/master/examples/sealed.py

The PR above transpiles a sealed class into a format accepted by z3 -smt2.

Note that the @Sealed proposal above is not identical to what was proposed in PEP 622. Specifically it doesn't use inheritance.