How to change dataset after each epoch?

[VietTralala]

I want to change my dataset after each training epoch. So I created a Callback and implemented on_train_epoch_end(self,trainer,pl_module) and on_validation_epoch_end(self,trainer,pl_module) which will call a datamodule function using the passed trainer as follows:
trainer.datamodule.switch_dataset(...)

I implemented the switch_dataset(..) function for my custom LightningDataModule which changes the attribute self.dataset of the LightningDataModule. This would then effect the train_dataloder and val_dataloader calls. However I can't access the switch_dataset() function. Python always complains with: AttributeError: 'MyDataModule' object has no attribute 'switch_dataset' eventhough the class definition is correct. What am I doing wrong/How can I achieve to switch datasets after each epoch?

Please delete/ignore this question. My issue was unrelated to pytorch lightning