Add strip_accents to basic BertTokenizer. (#6280)

* Add strip_accents to basic tokenizer

* Add tests for strip_accents.

* fix style with black

* Fix strip_accents test

* empty commit to trigger CI

* Improved strip_accents check

* Add code quality with is not False

src/transformers/tokenization_bert.py

@@ -154,6 +154,9 @@ class BertTokenizer(PreTrainedTokenizer):
             Whether to tokenize Chinese characters.
             This should likely be deactivated for Japanese:
             see: https://github.com/huggingface/transformers/issues/328
+        strip_accents: (:obj:`bool`, `optional`, defaults to :obj:`None`):
+            Whether to strip all accents. If this option is not specified (ie == None),
+            then it will be determined by the value for `lowercase` (as in the original Bert).
     """
 
     vocab_files_names = VOCAB_FILES_NAMES
@@ -173,6 +176,7 @@ class BertTokenizer(PreTrainedTokenizer):
         cls_token="[CLS]",
         mask_token="[MASK]",
         tokenize_chinese_chars=True,
+        strip_accents=None,
         **kwargs
     ):
         super().__init__(
@@ -194,7 +198,10 @@ class BertTokenizer(PreTrainedTokenizer):
         self.do_basic_tokenize = do_basic_tokenize
         if do_basic_tokenize:
             self.basic_tokenizer = BasicTokenizer(
-                do_lower_case=do_lower_case, never_split=never_split, tokenize_chinese_chars=tokenize_chinese_chars
+                do_lower_case=do_lower_case,
+                never_split=never_split,
+                tokenize_chinese_chars=tokenize_chinese_chars,
+                strip_accents=strip_accents,
             )
         self.wordpiece_tokenizer = WordpieceTokenizer(vocab=self.vocab, unk_token=self.unk_token)
 
@@ -351,7 +358,7 @@ class BertTokenizer(PreTrainedTokenizer):
 class BasicTokenizer(object):
     """Runs basic tokenization (punctuation splitting, lower casing, etc.)."""
 
-    def __init__(self, do_lower_case=True, never_split=None, tokenize_chinese_chars=True):
+    def __init__(self, do_lower_case=True, never_split=None, tokenize_chinese_chars=True, strip_accents=None):
         """ Constructs a BasicTokenizer.
 
         Args:
@@ -364,12 +371,16 @@ class BasicTokenizer(object):
                 Whether to tokenize Chinese characters.
                 This should likely be deactivated for Japanese:
                 see: https://github.com/huggingface/pytorch-pretrained-BERT/issues/328
+            **strip_accents**: (`optional`) boolean (default None)
+                Whether to strip all accents. If this option is not specified (ie == None),
+                then it will be determined by the value for `lowercase` (as in the original Bert).
         """
         if never_split is None:
             never_split = []
         self.do_lower_case = do_lower_case
         self.never_split = set(never_split)
         self.tokenize_chinese_chars = tokenize_chinese_chars
+        self.strip_accents = strip_accents
 
     def tokenize(self, text, never_split=None):
         """ Basic Tokenization of a piece of text.
@@ -395,9 +406,13 @@ class BasicTokenizer(object):
         orig_tokens = whitespace_tokenize(text)
         split_tokens = []
         for token in orig_tokens:
-            if self.do_lower_case and token not in never_split:
-                token = token.lower()
-                token = self._run_strip_accents(token)
+            if token not in never_split:
+                if self.do_lower_case:
+                    token = token.lower()
+                    if self.strip_accents is not False:
+                        token = self._run_strip_accents(token)
+                elif self.strip_accents:
+                    token = self._run_strip_accents(token)
             split_tokens.extend(self._run_split_on_punc(token, never_split))
 
         output_tokens = whitespace_tokenize(" ".join(split_tokens))

tests/test_tokenization_bert.py

@@ -130,6 +130,30 @@ class BertTokenizationTest(TokenizerTesterMixin, unittest.TestCase):
         )
         self.assertListEqual(tokenizer.tokenize("H\u00E9llo"), ["hello"])
 
+    def test_basic_tokenizer_lower_strip_accents_false(self):
+        tokenizer = BasicTokenizer(do_lower_case=True, strip_accents=False)
+
+        self.assertListEqual(
+            tokenizer.tokenize(" \tHäLLo!how  \n Are yoU?  "), ["hällo", "!", "how", "are", "you", "?"]
+        )
+        self.assertListEqual(tokenizer.tokenize("H\u00E9llo"), ["h\u00E9llo"])
+
+    def test_basic_tokenizer_lower_strip_accents_true(self):
+        tokenizer = BasicTokenizer(do_lower_case=True, strip_accents=True)
+
+        self.assertListEqual(
+            tokenizer.tokenize(" \tHäLLo!how  \n Are yoU?  "), ["hallo", "!", "how", "are", "you", "?"]
+        )
+        self.assertListEqual(tokenizer.tokenize("H\u00E9llo"), ["hello"])
+
+    def test_basic_tokenizer_lower_strip_accents_default(self):
+        tokenizer = BasicTokenizer(do_lower_case=True)
+
+        self.assertListEqual(
+            tokenizer.tokenize(" \tHäLLo!how  \n Are yoU?  "), ["hallo", "!", "how", "are", "you", "?"]
+        )
+        self.assertListEqual(tokenizer.tokenize("H\u00E9llo"), ["hello"])
+
     def test_basic_tokenizer_no_lower(self):
         tokenizer = BasicTokenizer(do_lower_case=False)
 
@@ -137,6 +161,20 @@ class BertTokenizationTest(TokenizerTesterMixin, unittest.TestCase):
             tokenizer.tokenize(" \tHeLLo!how  \n Are yoU?  "), ["HeLLo", "!", "how", "Are", "yoU", "?"]
         )
 
+    def test_basic_tokenizer_no_lower_strip_accents_false(self):
+        tokenizer = BasicTokenizer(do_lower_case=False, strip_accents=False)
+
+        self.assertListEqual(
+            tokenizer.tokenize(" \tHäLLo!how  \n Are yoU?  "), ["HäLLo", "!", "how", "Are", "yoU", "?"]
+        )
+
+    def test_basic_tokenizer_no_lower_strip_accents_true(self):
+        tokenizer = BasicTokenizer(do_lower_case=False, strip_accents=True)
+
+        self.assertListEqual(
+            tokenizer.tokenize(" \tHäLLo!how  \n Are yoU?  "), ["HaLLo", "!", "how", "Are", "yoU", "?"]
+        )
+
     def test_basic_tokenizer_respects_never_split_tokens(self):
         tokenizer = BasicTokenizer(do_lower_case=False, never_split=["[UNK]"])