what’s wrong with this data_loder?
It seems you might be using a 3rd party DataLoader implementation defined in pytorch-deeplab-xception/dataloaders/__init__.py, which raises the NotImplementedError, so should check this file and make sure this class is used as expected.
PS: you can post code snippets by wrapping them into three backticks ```, which makes debugging easier. 
Could you post an executable code snippet, so that we could take a look, please?