a context for helping with explicit transaction managers

tm.py

from contextlib import contextmanager, suppress
from transaction.interfaces import NoTransaction

class DoomedAbort(Exception):
    pass

@contextmanager
def tm_context(tm):
    tm.begin()
    try:
        yield tm.get()
        with suppress(NoTransaction):
            if tm.isDoomed():
                raise DoomedAbort

            tm.commit()

    except DoomedAbort:
        with suppress(NoTransaction):
            tm.abort()

    except BaseException as ex:
        with suppress(NoTransaction):
            tm.abort()

        raise ex