Python: use_twisted Decorator

This is a decorator that you can put on a Python function that will temporarily fire up Twisted's reactor and run a function under Twisted. This is useful if most of your program doesn't use Twisted, but you have a function that must use Twisted.

Here's an example of using it:

@use_twisted
@defer.inlineCallbacks
def do_something_twisted():
    value = yield do_something_else_twisted()
    other_value = yield do_more_stuff()
    defer.returnValue(value + other_value)

Here's the decorator:

def use_twisted(twisted_function):

    """This is a decorator to run a function under Twisted.

    Temporarily fire up the reactor and run the function under Twisted.
    It should return a deferred, of course.

    Unfortunately, there's a bug in Twisted that only allows you to
    start and stop the reactor once.  See
    http://jjinux.blogspot.com/2011/01/python-usetwisted-decorator.html.
    Hence, this decorator will prevent you from calling it twice.  So
    sorry :(

    """

    from twisted.python.failure import Failure

    captured_value = []  # Think of this as a box.

    def wrapper(*args, **kargs):
        reactor.callLater(0, call_twisted_function, twisted_function, args,
                          kargs)
        reactor.run()
        assert captured_value
        value = captured_value[0]
        if isinstance(value, (Exception, Failure)):
            raise value
        else:
            return value

    def call_twisted_function(twisted_function, args, kargs):
        deferred = twisted_function(*args, **kargs)
        deferred.addBoth(capture_and_stop)

    def capture_and_stop(value):
        captured_value.append(value)
        reactor.callLater(0, reactor.stop)
        return value

    if globals().get("_reactor_run", False):
        raise AssertionError("The use_twisted decorator can only be used once")
    else:
        globals()["_reactor_run"] = True

    return wrapper

Updated: Added code to prevent the decorator from being called twice.