Fixing backward compatiblity for non prefixed tokens (B-, I-).

src/transformers/pipelines/token_classification.py

@@ -411,7 +411,8 @@ def get_tag(self, entity_name: str) -> Tuple[str, str]:
             tag = entity_name[2:]
         else:
             # It's not in B-, I- format
-            bi = "B"
+            # Default to I- for continuation.
+            bi = "I"
             tag = entity_name
         return bi, tag
 

tests/test_pipelines_token_classification.py

@@ -318,6 +318,59 @@ def test_aggregation_strategy_byte_level_tokenizer(self):
             ],
         )
 
+    @require_torch
+    def test_aggregation_strategy_no_b_i_prefix(self):
+        model_name = "sshleifer/tiny-dbmdz-bert-large-cased-finetuned-conll03-english"
+        tokenizer = AutoTokenizer.from_pretrained(model_name, use_fast=True)
+        token_classifier = pipeline(task="ner", model=model_name, tokenizer=tokenizer, framework="pt")
+        # Just to understand scores indexes in this test
+        token_classifier.model.config.id2label = {0: "O", 1: "MISC", 2: "PER", 3: "ORG", 4: "LOC"}
+        example = [
+            {
+                # fmt : off
+                "scores": np.array([0, 0, 0, 0, 0.9968166351318359]),
+                "index": 1,
+                "is_subword": False,
+                "word": "En",
+                "start": 0,
+                "end": 2,
+            },
+            {
+                # fmt : off
+                "scores": np.array([0, 0, 0, 0, 0.9957635998725891]),
+                "index": 2,
+                "is_subword": True,
+                "word": "##zo",
+                "start": 2,
+                "end": 4,
+            },
+            {
+                # fmt: off
+                "scores": np.array([0, 0, 0, 0.9986497163772583, 0]),
+                # fmt: on
+                "index": 7,
+                "word": "UN",
+                "is_subword": False,
+                "start": 11,
+                "end": 13,
+            },
+        ]
+        self.assertEqual(
+            nested_simplify(token_classifier.aggregate(example, AggregationStrategy.NONE)),
+            [
+                {"end": 2, "entity": "LOC", "score": 0.997, "start": 0, "word": "En", "index": 1},
+                {"end": 4, "entity": "LOC", "score": 0.996, "start": 2, "word": "##zo", "index": 2},
+                {"end": 13, "entity": "ORG", "score": 0.999, "start": 11, "word": "UN", "index": 7},
+            ],
+        )
+        self.assertEqual(
+            nested_simplify(token_classifier.aggregate(example, AggregationStrategy.SIMPLE)),
+            [
+                {"entity_group": "LOC", "score": 0.996, "word": "Enzo", "start": 0, "end": 4},
+                {"entity_group": "ORG", "score": 0.999, "word": "UN", "start": 11, "end": 13},
+            ],
+        )
+
     @require_torch
     def test_aggregation_strategy(self):
         model_name = "sshleifer/tiny-dbmdz-bert-large-cased-finetuned-conll03-english"