Where exactly does the data loader access the disk?

Hi, I needed to know where the data loader opens the file to read/ access the disk?
In the fetch function below, I can see that we get the data. But, I’m not exactly able to find out where getitem is defined exactly?

One possible explanation could be that getitem could be used from the custom datasets. Example: datasets/mnist.py. Where load_data calls read_sn3_pascalvincent_tensor and this function internally access the file by opening like so :

The __getitem__ method is defined in your Dataset.