wrapping existing instance in new interface

[insyte at gmail.com]

I am writing a class that subclasses datetime.datetime in order to add
a few specialized methods.  So far the __init__ looks like this:

class myDateTime(datetime.datetime):
    def __init__(self, time, *args, **kwargs):
        if isinstance(time, str):
            timeTuple, tzOffset = self.magicMethod(timeStr)
            datetime.__init__(self, tzinfo=GenericTZ(tzoffset),
**timeTuple)

I would also like to pass in instances of datetime.datetime and have my
class wrap it in the new interface.  Something like this:

mdt = myDateTime(datetime.datetime.now())

I suppose I could do something like this:

    elif isinstance(time, datetime.datetime):
        timetuple = time.timetuple()
        tzoffset = time.utcoffset()
        datetime.__init__(self, tzinfo=GenericTZ(tzoffset),
**timetuple)

However, that feels rather... awkward.  Is there a better/cleaner way?
Perhaps a way to directly wrap my new interface around the passed-in
datetime.datetime instance?

Thanks...

-Ben