RobertaTokenizer token type issue
## ❓ Questions & Help

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Why the two middle `<\s>` are both assigned with token type 0?

https://github.com/huggingface/transformers/blob/e92bcb7eb6c5b9b6ed313cc74abaab50b3dc674f/transformers/tokenization_roberta.py#L149

Could this one be better?
```python
return len(cls + token_ids_0 + sep) * [0] + len(sep + token_ids_1 + sep) * [1] 
```
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<|||||>having the same question... why add two seps instead of one? 