tokenizer decode method
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- `transformers` version: 4.1.1
- Platform: Windows-10-10.0.19041-SP0
- Python version: 3.7.9
- PyTorch version (GPU?): 1.7.1+cu101 (True)
- Tensorflow version (GPU?): not installed (NA)
- Using GPU in script?: No
- Using distributed or parallel set-up in script?: No

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 albert, bert, GPT2, XLM: @LysandreJik
 tokenizers: @mfuntowicz
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 Speed and Memory Benchmarks: @patrickvonplaten
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 TextGeneration: @TevenLeScao
 examples/distillation: @VictorSanh
 nlp datasets: [different repo](https://github.com/huggingface/nlp)
 rust tokenizers: [different repo](https://github.com/huggingface/tokenizers)
 Text Generation: @patrickvonplaten @TevenLeScao
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@mfuntowicz

## Information

When I learn the source code of the tokenizer method `decode`, I found a problem in the **line 719 of the file `tokenization_utils.py`**. In my view, the type of the variable `token` is `str`, while the type of the property `all_special_ids` is `List[int]`. Although this problem will not raise error, even has no effect to the `decode` method, I still think this is a case which is need to be fixed for us to understand.


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## Expected behavior

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I think it is required to replace `self.all_special_ids` with `self.all_special_tokens` in the **line 719 of the file `tokenization_utils.py`**.
This issue has been automatically marked as stale and been closed because it has not had recent activity. Thank you for your contributions.

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