Fix skip_special_tokens for Wav2Vec2CTCTokenizer._decode

[msublee]

What does this PR do?

Fixes #29243

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@ArthurZucker

[ArthurZucker]

Thanks! Do you mind adding a small test to make sure all special tokens are now skipped?

[msublee]

I'm unfamiliar with this kind of PR (to big repo). Where and How should I add a small test?

[ArthurZucker]

There is a test here:

transformers/tests/models/wav2vec2/test_tokenization_wav2vec2.py

Line 453 in d03de1c

def test_tokenizer_decode_added_tokens(self):

but it seems to not properly test so let's update it 😉

[msublee]

I updated the test!
Also, I excluded the pad_token filtering in _decode since pad_token is used as CTC-blank token and is filtered in convert_tokens_to_string.

transformers/src/transformers/models/wav2vec2/tokenization_wav2vec2.py

Line 321 in b27aa20

processed_chars = list(filter(lambda char: char != self.pad_token, chars))

Finally, I applied this update to both Wav2Vec2Tokenizer and Wav2Vec2CTCTokenizer.

[ArthurZucker]

Overall LGTM, we need to test a bit more, and I'll ask @sanchit-gandhi his expertise on this model and a second look 👀

[ArthurZucker]

let's add a new token, like "<new_tokens>" and test that we can encode decode as we expect for both fast and slow tokenizers! 🤗

[msublee]

Is there a fast Wav2Vec2CTCTokenizer? I can't find it!

[ArthurZucker]

Sorry there is no fast tokenizer here! my bad. Let's just use other tokens than <unk>!

[msublee]

Sorry for the late. I updated it.

[HuggingFaceDocBuilderDev]

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[ArthurZucker]

Perfect thanks!