'Returns the :class:`.Engine` or :class:`.Connection` to
which this :class:`.Executable` is bound, or None if none found.
This is a traversal which checks locally, then
checks among the "from" clauses of associated objects
until a bound engine or connection is found.'

@property
def bind(self):

    if (self._bind is not None):
        return self._bind
    for f in _from_objects(self):
        if (f is self):
            continue
        engine = f.bind
        if (engine is not None):
            return engine
    else:
        return None
