test.py

import time

from tornado import ioloop, gen
from tornado.stack_context import ExceptionStackContext

@gen.engine
def handle():
    def _exc(typ, val, tb):
        go()
        return False

    print 'handle'

    with ExceptionStackContext(_exc):
        # Some fancy async code here, can't use try/catch
        # result = yield gen.Task(...)
        raise Exception('Foobar')

        print '.. success'


def go():
    print 'queued'
    io_loop.add_timeout(time.time() + 1, handle)

# Initialization
io_loop = ioloop.IOLoop().instance()

go()

io_loop.start()