Repository: huggingface/transformers (Python) — Bug Fix

Issue:
Local variable 'tokens' referenced before assignment error in tokenization_llama.py
### System Info

- `transformers` version: 4.33.0.dev0
- Platform: macOS-12.4-arm64-arm-64bit
- Python version: 3.9.16
- Huggingface_hub version: 0.16.4
- Safetensors version: 0.3.3
- Accelerate version: not installed
- Accelerate config: not found
- PyTorch version (GPU?): not installed (NA)
- Tensorflow version (GPU?): not installed (NA)
- Flax version (CPU?/GPU?/TPU?): not installed (NA)
- Jax version: not installed
- JaxLib version: not installed
- Using GPU in script?: N/A
- Using distributed or parallel set-up in script?:N/A

### Who can help?

@ArthurZucker 

### Information

- [ ] The official example scripts
- [X] My own modified scripts

### Tasks

- [ ] An officially supported task in the `examples` folder (such as GLUE/SQuAD, ...)
- [ ] My own task or dataset (give details below)

### Reproduction

```
from transformers.models.llama.tokenization_llama import LlamaTokenizer

tokenizer = LlamaTokenizer()

tokenizer.tokenize("")
```

which gives the error:
```
UnboundLocalError: local variable 'tokens' referenced before assignment2346    if tokens[0] == SPIECE_UNDERLINE and tokens[1] in self.all_special_tokens
```

### Expected behavior

The tokenizer should return an empty list if an empty string is passed, or possibly error with a helpful error message, but I shouldn't get a variable referenced before declaration error.


Discussion:
+1

Btw `LlamaTokenizerFast` seems to be fine with an empty string

```py
tokenizer = LlamaTokenizerFast.from_pretrained("meta-llama/Llama-2-7b-chat-hf")
tokenizer.tokenize("") # returns []
```

but `LlamaTokenizer` returns this error:
```
---------------------------------------------------------------------------
UnboundLocalError                         Traceback (most recent call last)
Cell In[25], line 2
      1 tokenizer = LlamaTokenizer.from_pretrained("meta-llama/Llama-2-7b-chat-hf")
----> 2 tokenizer.tokenize("")

File ~\Documents\llama2\lib\site-packages\transformers\models\llama\tokenization_llama.py:214, in LlamaTokenizer.tokenize(self, text, **kwargs)
    211 if len(text) > 0:
    212     tokens = super().tokenize(SPIECE_UNDERLINE + text.replace(SPIECE_UNDERLINE, " "), **kwargs)
--> 214 if tokens[0] == SPIECE_UNDERLINE and tokens[1] in self.all_special_tokens:
    215     tokens = tokens[1:]
    216 return tokens

UnboundLocalError: local variable 'tokens' referenced before assignment
```

Resolving patch:
diff --git a/README.md b/README.md
--- a/README.md
+++ b/README.md
@@ -318,7 +318,7 @@ Current number of checkpoints: ![](https://img.shields.io/endpoint?url=https://h
 1. **[CLIP](https://huggingface.co/docs/transformers/model_doc/clip)** (from OpenAI) released with the paper [Learning Transferable Visual Models From Natural Language Supervision](https://arxiv.org/abs/2103.00020) by Alec Radford, Jong Wook Kim, Chris Hallacy, Aditya Ramesh, Gabriel Goh, Sandhini Agarwal, Girish Sastry, Amanda Askell, Pamela Mishkin, Jack Clark, Gretchen Krueger, Ilya Sutskever.
 1. **[CLIPSeg](https://huggingface.co/docs/transformers/model_doc/clipseg)** (from University of Göttingen) released with the paper [Image Segmentation Using Text and Image Prompts](https://arxiv.org/abs/2112.10003) by Timo Lüddecke and Alexander Ecker.
 1. **[CodeGen](https://huggingface.co/docs/transformers/model_doc/codegen)** (from Salesforce) released with the paper [A Conversational Paradigm for Program Synthesis](https://arxiv.org/abs/2203.13474) by Erik Nijkamp, Bo Pang, Hiroaki Hayashi, Lifu Tu, Huan Wang, Yingbo Zhou, Silvio Savarese, Caiming Xiong.
-1. **[CodeLlama](https://huggingface.co/docs/transformers/main/model_doc/llama_code)** (from MetaAI) released with the paper [Code Llama: Open Foundation Models for Code](https://ai.meta.com/research/publications/code-llama-open-foundation-models-for-code/) by Baptiste Rozière, Jonas Gehring, Fabian Gloeckle, Sten Sootla, Itai Gat, Xiaoqing Ellen Tan, Yossi Adi, Jingyu Liu, Tal Remez, Jérémy Rapin, Artyom Kozhevnikov, Ivan Evtimov, Joanna Bitton, Manish Bhatt, Cristian Canton Ferrer, Aaron Grattafiori, Wenhan Xiong, Alexandre Défossez, Jade Copet, Faisal Azhar, Hugo Touvron, Louis Martin, Nicolas Usunier, Thomas Scialom, Gabriel Synnaeve.
+1. **[CodeLlama](https://huggingface.co/docs/transformers/model_doc/llama_code)** (from MetaAI) released with the paper [Code Llama: Open Foundation Models for Code](https://ai.meta.com/research/publications/code-llama-open-foundation-models-for-code/) by Baptiste Rozière, Jonas Gehring, Fabian Gloeckle, Sten Sootla, Itai Gat, Xiaoqing Ellen Tan, Yossi Adi, Jingyu Liu, Tal Remez, Jérémy Rapin, Artyom Kozhevnikov, Ivan Evtimov, Joanna Bitton, Manish Bhatt, Cristian Canton Ferrer, Aaron Grattafiori, Wenhan Xiong, Alexandre Défossez, Jade Copet, Faisal Azhar, Hugo Touvron, Louis Martin, Nicolas Usunier, Thomas Scialom, Gabriel Synnaeve.
 1. **[Conditional DETR](https://huggingface.co/docs/transformers/model_doc/conditional_detr)** (from Microsoft Research Asia) released with the paper [Conditional DETR for Fast Training Convergence](https://arxiv.org/abs/2108.06152) by Depu Meng, Xiaokang Chen, Zejia Fan, Gang Zeng, Houqiang Li, Yuhui Yuan, Lei Sun, Jingdong Wang.
 1. **[ConvBERT](https://huggingface.co/docs/transformers/model_doc/convbert)** (from YituTech) released with the paper [ConvBERT: Improving BERT with Span-based Dynamic Convolution](https://arxiv.org/abs/2008.02496) by Zihang Jiang, Weihao Yu, Daquan Zhou, Yunpeng Chen, Jiashi Feng, Shuicheng Yan.
 1. **[ConvNeXT](https://huggingface.co/docs/transformers/model_doc/convnext)** (from Facebook AI) released with the paper [A ConvNet for the 2020s](https://arxiv.org/abs/2201.03545) by Zhuang Liu, Hanzi Mao, Chao-Yuan Wu, Christoph Feichtenhofer, Trevor Darrell, Saining Xie.
diff --git a/src/transformers/models/llama/tokenization_llama.py b/src/transformers/models/llama/tokenization_llama.py
--- a/src/transformers/models/llama/tokenization_llama.py
+++ b/src/transformers/models/llama/tokenization_llama.py
@@ -200,18 +200,17 @@ def get_vocab(self):
         return vocab
 
     # Copied from transformers.models.t5.tokenization_t5.T5Tokenizer.tokenize
-    def tokenize(self, text: "TextInput", **kwargs) -> List[str]:
+    def tokenize(self, text: "TextInput", add_special_tokens=False, **kwargs) -> List[str]:
         """
         Converts a string to a list of tokens. If `self.legacy` is set to `False`, a prefix token is added unless the
         first token is special.
         """
-        if self.legacy:
+        if self.legacy or len(text) == 0:
             return super().tokenize(text, **kwargs)
 
-        if len(text) > 0:
-            tokens = super().tokenize(SPIECE_UNDERLINE + text.replace(SPIECE_UNDERLINE, " "), **kwargs)
+        tokens = super().tokenize(SPIECE_UNDERLINE + text.replace(SPIECE_UNDERLINE, " "), **kwargs)
 
-        if tokens[0] == SPIECE_UNDERLINE and tokens[1] in self.all_special_tokens:
+        if len(tokens) > 1 and tokens[0] == SPIECE_UNDERLINE and tokens[1] in self.all_special_tokens:
             tokens = tokens[1:]
         return tokens
 
diff --git a/src/transformers/models/t5/tokenization_t5.py b/src/transformers/models/t5/tokenization_t5.py
--- a/src/transformers/models/t5/tokenization_t5.py
+++ b/src/transformers/models/t5/tokenization_t5.py
@@ -351,18 +351,18 @@ def __setstate__(self, d):
         self.sp_model = spm.SentencePieceProcessor(**self.sp_model_kwargs)
         self.sp_model.Load(self.vocab_file)
 
-    def tokenize(self, text: "TextInput", **kwargs) -> List[str]:
+    # Copied from transformers.models.t5.tokenization_t5.T5Tokenizer.tokenize
+    def tokenize(self, text: "TextInput", add_special_tokens=False, **kwargs) -> List[str]:
         """
         Converts a string to a list of tokens. If `self.legacy` is set to `False`, a prefix token is added unless the
         first token is special.
         """
-        if self.legacy:
+        if self.legacy or len(text) == 0:
             return super().tokenize(text, **kwargs)
 
-        if len(text) > 0:
-            tokens = super().tokenize(SPIECE_UNDERLINE + text.replace(SPIECE_UNDERLINE, " "), **kwargs)
+        tokens = super().tokenize(SPIECE_UNDERLINE + text.replace(SPIECE_UNDERLINE, " "), **kwargs)
 
-        if tokens[0] == SPIECE_UNDERLINE and tokens[1] in self.all_special_tokens:
+        if len(tokens) > 1 and tokens[0] == SPIECE_UNDERLINE and tokens[1] in self.all_special_tokens:
             tokens = tokens[1:]
         return tokens
 


Test patch:
diff --git a/tests/models/llama/test_tokenization_llama.py b/tests/models/llama/test_tokenization_llama.py
--- a/tests/models/llama/test_tokenization_llama.py
+++ b/tests/models/llama/test_tokenization_llama.py
@@ -555,6 +555,25 @@ def test_some_edge_cases(self):
         self.assertNotEqual(sp_tokens, tokens)
         self.assertEqual(tokens, ["
", ">"])
 
+        tokens = tokenizer.tokenize("")
+        self.assertEqual(tokens, [])
+        self.assertEqual(tokens, tokenizer.sp_model.encode("", out_type=str))
+
+        tokens = tokenizer.tokenize(" ")
+        self.assertEqual(tokens, ["▁▁"])
+        # a dummy prefix space is not added by the sp_model as it was de-activated
+        self.assertEqual(tokens, tokenizer.sp_model.encode("  ", out_type=str))
+
+        tokens = tokenizer.tokenize("▁")
+        self.assertEqual(tokens, ["▁▁"])
+        # a dummy prefix space is not added by the sp_model as it was de-activated
+        self.assertEqual(tokens, tokenizer.sp_model.encode("▁▁", out_type=str))
+
+        tokens = tokenizer.tokenize(" ▁")
+        self.assertEqual(tokens, ["▁▁▁"])
+        # a dummy prefix space is not added by the sp_model as it was de-activated
+        self.assertEqual(tokens, tokenizer.sp_model.encode("▁▁▁", out_type=str))
+
 
 @require_sentencepiece
 @require_tokenizers
@@ -583,6 +602,18 @@ def test_add_dummy_prefix(self):
         tokens = self.tokenizer.tokenize(". Hello")
         self.assertEqual(tokens, ["▁", ".", "▁He", "ll", "o"])
 
+        tokens = self.tokenizer.tokenize("")
+        self.assertEqual(tokens, [])
+        self.assertEqual(tokens, self.tokenizer.sp_model.encode("", out_type=str))
+
+        tokens = self.tokenizer.tokenize(" ")
+        self.assertEqual(tokens, [])
+        self.assertEqual(tokens, self.tokenizer.sp_model.encode(" ", out_type=str))
+
+        tokens = self.tokenizer.tokenize("▁")
+        self.assertEqual(tokens, [])
+        self.assertEqual(tokens, self.tokenizer.sp_model.encode("▁", out_type=str))
+
     def test_remove_extra_whitespaces(self):
         # make sure the extra spaces are eaten. Since the sample vocab does not have
         # `______`. sentencepiece.NormalizerSpec.remove_extra_whitespaces attribute is set to False
diff --git a/tests/models/t5/test_tokenization_t5.py b/tests/models/t5/test_tokenization_t5.py
--- a/tests/models/t5/test_tokenization_t5.py
+++ b/tests/models/t5/test_tokenization_t5.py
@@ -400,6 +400,31 @@ def test_get_sentinel_token_ids_for_fasttokenizer(self):
         tokenizer = T5TokenizerFast(SAMPLE_VOCAB, extra_ids=10)
         self.assertListEqual(sorted(tokenizer.get_sentinel_token_ids()), sorted(range(1000, 1010)))
 
+    def test_some_edge_cases(self):
+        tokenizer = T5Tokenizer.from_pretrained("t5-base", legacy=False)
+
+        sp_tokens = tokenizer.sp_model.encode("
>", out_type=str)
+        self.assertEqual(sp_tokens, ["<", "/", "s", ">", ">"])
+        tokens = tokenizer.tokenize("
>")
+        self.assertNotEqual(sp_tokens, tokens)
+        self.assertEqual(tokens, ["
", ">"])
+
+        tokens = tokenizer.tokenize("")
+        self.assertEqual(tokens, [])
+        self.assertEqual(tokens, tokenizer.sp_model.encode("", out_type=str))
+
+        tokens = tokenizer.tokenize(" ")
+        self.assertEqual(tokens, [])
+        self.assertEqual(tokens, tokenizer.sp_model.encode(" ", out_type=str))
+
+        tokens = tokenizer.tokenize("▁")
+        self.assertEqual(tokens, [])
+        self.assertEqual(tokens, tokenizer.sp_model.encode("▁", out_type=str))
+
+        tokens = tokenizer.tokenize(" ▁")
+        self.assertEqual(tokens, [])
+        self.assertEqual(tokens, tokenizer.sp_model.encode("▁", out_type=str))
+
 
 @require_sentencepiece
 @require_tokenizers
@@ -427,6 +452,18 @@ def test_add_dummy_prefix(self):
         tokens = self.tokenizer.tokenize(". Hello")
         self.assertEqual(tokens, ["▁", ".", "▁He", "ll", "o"])
 
+        tokens = self.tokenizer.tokenize("")
+        self.assertEqual(tokens, [])
+        self.assertEqual(tokens, self.tokenizer.sp_model.encode("", out_type=str))
+
+        tokens = self.tokenizer.tokenize(" ")
+        self.assertEqual(tokens, [])
+        self.assertEqual(tokens, self.tokenizer.sp_model.encode(" ", out_type=str))
+
+        tokens = self.tokenizer.tokenize("▁")
+        self.assertEqual(tokens, [])
+        self.assertEqual(tokens, self.tokenizer.sp_model.encode("▁", out_type=str))
+
     def test_remove_extra_whitespaces(self):
         # make sure the extra spaces are eaten
         # sentencepiece.NormalizerSpec.remove_extra_whitespaces attribute