⚠️⚠️[`T5Tokenize`] Fix T5 family tokenizers⚠️⚠️ (#24565)

* don't add space before single letter chars that don't have a merge

* fix the fix

* fixup

* add a test

* more testing

* fixup

* hack to make sure fast is also fixed

* update switch transformers test

* revert convert slow

* Update src/transformers/models/t5/tokenization_t5.py
Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>

* add typechecking

* quality

---------
Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>

src/transformers/models/t5/tokenization_t5.py

@@ -19,11 +19,15 @@ import os
 import re
 import warnings
 from shutil import copyfile
-from typing import Any, Dict, List, Optional, Tuple
+from typing import TYPE_CHECKING, Any, Dict, List, Optional, Tuple
 
 import sentencepiece as spm
 
 from ...tokenization_utils import PreTrainedTokenizer
+
+
+if TYPE_CHECKING:
+    from ...tokenization_utils_base import TextInput
 from ...utils import logging
 
 
@@ -51,6 +55,8 @@ PRETRAINED_POSITIONAL_EMBEDDINGS_SIZES = {
     "t5-11b": 512,
 }
 
+SPIECE_UNDERLINE = "▁"
+
 
 class T5Tokenizer(PreTrainedTokenizer):
     """
@@ -294,9 +300,17 @@ class T5Tokenizer(PreTrainedTokenizer):
         self.sp_model = spm.SentencePieceProcessor(**self.sp_model_kwargs)
         self.sp_model.Load(self.vocab_file)
 
+    def tokenize(self, text: "TextInput", **kwargs) -> List[str]:
+        if not text.startswith(" "):
+            text = " " + text
+        return super().tokenize(text, **kwargs)
+
     def _tokenize(self, text: str) -> List[str]:
         """Take as input a string and return a list of strings (tokens) for words/sub-words"""
-        return self.sp_model.encode(text, out_type=str)
+        tokens = self.sp_model.encode(text, out_type=str)
+        if not text.startswith(" ") and tokens[0] == SPIECE_UNDERLINE:
+            tokens = tokens[1:]
+        return tokens
 
     def _convert_token_to_id(self, token):
         """Converts a token (str) in an id using the vocab."""

tests/models/switch_transformers/test_modeling_switch_transformers.py

@@ -1149,7 +1149,7 @@ class SwitchTransformerModelIntegrationTests(unittest.TestCase):
         model = SwitchTransformersForConditionalGeneration.from_pretrained(
             "google/switch-base-8", torch_dtype=torch.bfloat16
         ).eval()
-        tokenizer = AutoTokenizer.from_pretrained("t5-small")
+        tokenizer = AutoTokenizer.from_pretrained("t5-small", use_fast=False)
         model = model.to(torch_device)
 
         input_ids = tokenizer(
@@ -1160,13 +1160,13 @@ class SwitchTransformerModelIntegrationTests(unittest.TestCase):
         self.assertEqual(output_str, "drink.")
 
         input_ids = tokenizer(
-            "A <extra_id_0> walks into a bar a orders a <extra_id_1> with <extra_id_2> pinch of <extra_id_3>.",
+            "A <extra_id_0> walks into a bar and orders a <extra_id_1> with <extra_id_2> pinch of <extra_id_3>.",
             return_tensors="pt",
         ).input_ids.to(torch_device)
         sequences = model.generate(input_ids)
         output_str = tokenizer.batch_decode(sequences, skip_special_tokens=False)[0]
 
-        EXPECTED_OUTPUT = "<pad><extra_id_0> man<extra_id_1> beer<extra_id_2> a<extra_id_3> salt<extra_id_4>.</s>"
+        EXPECTED_OUTPUT = "<pad><extra_id_0> man<extra_id_1> beer<extra_id_2> a<extra_id_3> whiskey<extra_id_4>.</s>"
         self.assertEqual(output_str, EXPECTED_OUTPUT)
 
     def test_small_batch_generate(self):
@@ -1174,10 +1174,10 @@ class SwitchTransformerModelIntegrationTests(unittest.TestCase):
         model = SwitchTransformersForConditionalGeneration.from_pretrained(
             "google/switch-base-8", torch_dtype=torch.bfloat16
         ).eval()
-        tokenizer = AutoTokenizer.from_pretrained("t5-small")
+        tokenizer = AutoTokenizer.from_pretrained("t5-small", use_fast=False)
 
         inputs = [
-            "A <extra_id_0> walks into a bar a orders a <extra_id_1> with <extra_id_2> pinch of <extra_id_3>."
+            "A <extra_id_0> walks into a bar and orders a <extra_id_1> with <extra_id_2> pinch of <extra_id_3>."
         ] * BATCH_SIZE
         encoded_input = tokenizer.batch_encode_plus(inputs, return_tensors="pt")
 

tests/models/t5/test_tokenization_t5.py

@@ -399,3 +399,35 @@ class T5TokenizationTest(TokenizerTesterMixin, unittest.TestCase):
     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_encode_extra_ids(self):
+        tokenizer = T5Tokenizer(SAMPLE_VOCAB, extra_ids=0)
+        tokenizer.add_special_tokens({"additional_special_tokens": ["<extra_id_0>"]})
+        tokenizer._create_trie(tokenizer.all_special_tokens)
+        # TODO ArthurZ the above is necessary as addedTokens / intialization sucks. Trie is not correctly created
+        # So the extra ids are split....
+
+        input_ids = tokenizer.encode(". Hello")
+        self.assertEquals(input_ids, [7, 4, 156, 86, 20, 2])
+        tokens = tokenizer.tokenize(". Hello")
+        self.assertEquals(tokens, ["▁", ".", "▁He", "ll", "o"])
+
+        input_ids = tokenizer.encode(" . Hello")
+        self.assertEquals(input_ids, [7, 4, 156, 86, 20, 2])
+        tokens = tokenizer.tokenize(" . Hello")
+        self.assertEquals(tokens, ["▁", ".", "▁He", "ll", "o"])
+
+        input_ids = tokenizer.encode("Hello, <extra_id_0>I")
+        self.assertEquals(input_ids, [156, 86, 20, 3, 999, 8, 2])
+        tokens = tokenizer.tokenize("Hello, <extra_id_0>I")
+        self.assertEquals(tokens, ["▁He", "ll", "o", ",", "<extra_id_0>", "▁I"])
+
+        input_ids = tokenizer.encode("Hello, <extra_id_0>,")
+        self.assertEquals(input_ids, [156, 86, 20, 3, 999, 3, 2])
+        tokens = tokenizer.tokenize("Hello, <extra_id_0>,")
+        self.assertEquals(tokens, ["▁He", "ll", "o", ",", "<extra_id_0>", ","])
+
+        input_ids = tokenizer.encode(" <extra_id_0> ,")
+        self.assertEquals(input_ids, [999, 3, 2])
+        tokens = tokenizer.tokenize(" <extra_id_0> ,")
+        self.assertEquals(tokens, ["<extra_id_0>", ","])  # spaces are eaten by rstrip / lstrip