'Implement a safe copy.copy().
SQLAlchemy-mapped objects travel with an object
called an InstanceState, which is pegged to that object
specifically and tracks everything about that object.  It\'s
critical within all attribute operations, including gets
and deferred loading.   This object definitely cannot be
shared among two instances, and must be handled.
The copy routine here makes use of session.merge() which
already essentially implements a "copy" style of operation,
which produces a new instance with a new InstanceState and copies
all the data along mapped attributes without using any SQL.
The mode we are using here has the caveat that the given object
must be "clean", e.g. that it has no database-loaded state
that has been updated and not flushed.   This is a good thing,
as creating a copy of an object including non-flushed, pending
database state is probably not a good idea; neither represents
what the actual row looks like, and only one should be flushed.'

def __copy__(self):

    session = orm.Session()
    copy = session.merge(self, load=False)
    session.expunge(copy)
    return copy
