pytorchでのDataset作成方法

pytorchのtorch.utils.data.Datasetを用いて自作でデータセットを作ろうとしたのですが，エラーが発生してしまいます．
自分なりに調べたのですが解決できないため詳しい方いらっしゃいましたら教えていただけましたら幸いです．
以下私のコードです．

python
1class DataSets(torch.utils.data.Dataset):
2    def __init__(self,imgdir,lbldir,tfms):
3        
4        self.imgdir = imgdir
5        self.lbldir = lbldir
6        self.tfms = tfms
7        
8        self.tr = []
9        self.lbl = []
10        self.lb = pd.read_csv(self.lbldir+'/train.csv')
11        for i in range(1821):
12            self.tr_path = glob.glob((os.path.join(self.imgdir,f'Train_{i}.jpg')))
13            self.tr.append(tr_path)
14                                
15            self.lb = self.lb.iloc[:,1:]
16            self.lbl.append(self.lb.iloc[i,:])
17        
18        
19    def __len__(self):
20        return len(self.tr)
21                             
22    def __getitem__(self,idx):
23        img = np.array(Image.open(self.tr[idx]))
24        lbl = self.lbl[idx]
25                                  
26        if self.tfms:
27            img = self.tfms(img)
28        
29        return img, lbl

そして，transformを定義後にこのようにしてDataloaderを作成しました．

python
1bs = 8
2ds = DataSets(imgdir, lbldir, tfms)
3dl = torch.utils.data.DataLoader(ds, bs, shuffle=True)
4

ここまでは問題なく進行するのですが，確認のため以下のコードを入力するとエラーが生じます．

python
1for i in dl:
2    print(i)

error
1--------------------------------------------------------------------------
2AttributeError                            Traceback (most recent call last)
3/opt/conda/lib/python3.6/site-packages/PIL/Image.py in open(fp, mode)
4   2637     try:
5-> 2638         fp.seek(0)
6   2639     except (AttributeError, io.UnsupportedOperation):
7
8AttributeError: 'list' object has no attribute 'seek'
9
10During handling of the above exception, another exception occurred:
11
12AttributeError                            Traceback (most recent call last)
13<ipython-input-91-26c3503426c8> in <module>
14----> 1 for i in dl:
15      2     print(i)
16
17/opt/conda/lib/python3.6/site-packages/torch/utils/data/dataloader.py in __next__(self)
18    343 
19    344     def __next__(self):
20--> 345         data = self._next_data()
21    346         self._num_yielded += 1
22    347         if self._dataset_kind == _DatasetKind.Iterable and \
23
24/opt/conda/lib/python3.6/site-packages/torch/utils/data/dataloader.py in _next_data(self)
25    383     def _next_data(self):
26    384         index = self._next_index()  # may raise StopIteration
27--> 385         data = self._dataset_fetcher.fetch(index)  # may raise StopIteration
28    386         if self._pin_memory:
29    387             data = _utils.pin_memory.pin_memory(data)
30
31/opt/conda/lib/python3.6/site-packages/torch/utils/data/_utils/fetch.py in fetch(self, possibly_batched_index)
32     42     def fetch(self, possibly_batched_index):
33     43         if self.auto_collation:
34---> 44             data = [self.dataset[idx] for idx in possibly_batched_index]
35     45         else:
36     46             data = self.dataset[possibly_batched_index]
37
38/opt/conda/lib/python3.6/site-packages/torch/utils/data/_utils/fetch.py in <listcomp>(.0)
39     42     def fetch(self, possibly_batched_index):
40     43         if self.auto_collation:
41---> 44             data = [self.dataset[idx] for idx in possibly_batched_index]
42     45         else:
43     46             data = self.dataset[possibly_batched_index]
44
45<ipython-input-84-1f993d703f19> in __getitem__(self, idx)
46     23 
47     24     def __getitem__(self,idx):
48---> 25         img = np.array(Image.open(self.tr[idx]))
49     26         lbl = self.lbl[idx]
50     27 
51
52/opt/conda/lib/python3.6/site-packages/PIL/Image.py in open(fp, mode)
53   2638         fp.seek(0)
54   2639     except (AttributeError, io.UnsupportedOperation):
55-> 2640         fp = io.BytesIO(fp.read())
56   2641         exclusive_fp = True
57   2642 
58
59AttributeError: 'list' object has no attribute 'read'