9t_12.py

class MyModule(LightningModule):
    def __init__():
        self.encoder = RNN(...)
        self.decoder = RNN(...)
    def forward(x):
        # models won't be moved after the first forward because 
        # they are already on the correct GPUs
        self.encoder.cuda(0)
        self.decoder.cuda(1)
        out = self.encoder(x)
        out = self.decoder(out.cuda(1))
        
# don't pass GPUs to trainer
model = MyModule()
trainer = Trainer()
trainer.fit(model)