Make cache saving optional (#2977)

utils/datasets.py

@@ -502,8 +502,11 @@ class LoadImagesAndLabels(Dataset):  # for training/testing
         x['hash'] = get_hash(self.label_files + self.img_files)
         x['results'] = nf, nm, ne, nc, i + 1
         x['version'] = 0.1  # cache version
-        torch.save(x, path)  # save for next time
-        logging.info(f'{prefix}New cache created: {path}')
+        try:
+            torch.save(x, path)  # save for next time
+            logging.info(f'{prefix}New cache created: {path}')
+        except Exception as e:
+            logging.info(f'{prefix}WARNING: Cache directory {path.parent} is not writeable: {e}')  # path not writeable
         return x
 
     def __len__(self):