Fixing zero-shot backward compatiblity (#13725)

Fixes #13697

src/transformers/pipelines/zero_shot_classification.py

@@ -150,6 +150,7 @@ class ZeroShotClassificationPipeline(Pipeline):
     def __call__(
         self,
         sequences: Union[str, List[str]],
+        *args,
         **kwargs,
     ):
         """
@@ -183,6 +184,13 @@ class ZeroShotClassificationPipeline(Pipeline):
             - **scores** (:obj:`List[float]`) -- The probabilities for each of the labels.
         """
 
+        if len(args) == 0:
+            pass
+        elif len(args) == 1 and "candidate_labels" not in kwargs:
+            kwargs["candidate_labels"] = args[0]
+        else:
+            raise ValueError(f"Unable to understand extra arguments {args}")
+
         result = super().__call__(sequences, **kwargs)
         if len(result) == 1:
             return result[0]

tests/test_pipelines_zero_shot.py

@@ -37,6 +37,10 @@ class ZeroShotClassificationPipelineTests(unittest.TestCase, metaclass=PipelineT
         outputs = classifier("Who are you voting for in 2020?", candidate_labels="politics")
         self.assertEqual(outputs, {"sequence": ANY(str), "labels": [ANY(str)], "scores": [ANY(float)]})
 
+        # No kwarg
+        outputs = classifier("Who are you voting for in 2020?", ["politics"])
+        self.assertEqual(outputs, {"sequence": ANY(str), "labels": [ANY(str)], "scores": [ANY(float)]})
+
         outputs = classifier("Who are you voting for in 2020?", candidate_labels=["politics"])
         self.assertEqual(outputs, {"sequence": ANY(str), "labels": [ANY(str)], "scores": [ANY(float)]})