def delete(self, doc):
        if doc.id is None:
            raise DatabaseException('Document does not have id')
        if doc.sid is None:
            try:
                rs = self.db.docs.remove({'id': doc.id}, safe=True)
                assert rs['n'] == 1
            except Exception as e:
                raise DatabaseException(e)
            return None
        doc.data = None
        return self.update(doc)
def _rmsprop_update_numpy(self, var, g, mg, rms, mom, lr, decay, momentum,
                            centered):
    rms_t = rms * decay + (1 - decay) * g * g
    if centered:
      mg_t = mg * decay + (1 - decay) * g
      denom_t = rms_t - mg_t * mg_t
    else:
      mg_t = mg
      denom_t = rms_t
    mom_t = momentum * mom + lr * g / np.sqrt(denom_t, dtype=denom_t.dtype)
    var_t = var - mom_t
    return var_t, mg_t, rms_t, mom_t