i got this error when i train a model (srgan)

KeyError: Caught KeyError in DataLoader worker process 0.
Original Traceback (most recent call last):
File "/usr/local/lib/python3.6/dist-packages/torch/utils/data/_ut ils/worker.py", line 178, in _worker_loop
data = fetcher.fetch(index)
File "/usr/local/lib/python3.6/dist-packages/torch/utils/data/_ut ils/fetch.py", line 44, in fetch
data = [self.dataset[idx] for idx in possibly_batched_index]
File "/usr/local/lib/python3.6/dist-packages/torch/utils/data/_ut ils/fetch.py", line 44, in
data = [self.dataset[idx] for idx in possibly_batched_index]
File "/content/drive/My Drive/PyTorch--master/datasets.py", line 67, in getitem
img = Image.open(self.images[i], mode='r')
KeyError: 0
how how many epoch i should do to make a good model?
i'm training the model in google colab
thanks