Hi, I am trying to create several encoder blocks by using nn.ModuleList and I get NotImplementedError.

```
class Transformer(nn.Module):
def __init__(self,embed_size,num_heads,N,in_channels,batch_size,num_encoders,num_class):
super().__init__()
self.num_heads = num_heads
self.embed_size = embed_size
self.N = N
self.in_channels = in_channels
self.batch_size = batch_size
self.num_encoders = num_encoders
self.num_class = num_class
self.proj = Project(self.N,self.in_channels,self.embed_size,self.batch_size)
self.block = nn.ModuleList([nn.ModuleList([nn.LayerNorm(self.embed_size),EncoderBlock(self.embed_size,self.num_heads,self.N,self.in_channels,self.batch_size)]) for i in range(num_encoders)])
self.encoders = EncoderBlock(self.embed_size,self.num_heads,self.N,self.in_channels,self.batch_size)##nn.ModuleList( EncoderBlock(self.embed_size,self.num_heads,self.N,self.in_channels,self.batch_size) for i in range(num_encoders))
self.Linear = nn.Linear(self.embed_size,self.num_class)
self.layernorm = nn.LayerNorm(num_class)
indices = [i for i in range(self.num_class)]
self.indices = torch.tensor(indices)
def forward(self,img):
out = self.proj(img)
out = self.block(out) ## I got error here
out = self.Linear(torch.squeeze(torch.index_select(out,1,torch.tensor(self.N**2))))
out = self.layernorm(out)
return out
```

What is the problem or are the problems?

Thanks.