[DX fix] Fixing QA pipeline streaming a dataset. (#18516)

* [DX fix] Fixing QA pipeline streaming a dataset.

QuestionAnsweringArgumentHandler would iterate over the whole dataset
effectively killing all properties of the pipeline.
This restores nice properties when using `Dataset` or `Generator` since
those are meant to be consumed lazily.

* Handling TF better.

src/transformers/pipelines/question_answering.py

+import types
 import warnings
 from collections.abc import Iterable
 from typing import TYPE_CHECKING, Dict, List, Optional, Tuple, Union
@@ -22,8 +23,11 @@ if is_tf_available():
 
     from ..models.auto.modeling_tf_auto import TF_MODEL_FOR_QUESTION_ANSWERING_MAPPING
 
+    Dataset = None
+
 if is_torch_available():
     import torch
+    from torch.utils.data import Dataset
 
     from ..models.auto.modeling_auto import MODEL_FOR_QUESTION_ANSWERING_MAPPING
 
@@ -82,6 +86,11 @@ class QuestionAnsweringArgumentHandler(ArgumentHandler):
         else:
             raise ValueError(f"Unknown arguments {kwargs}")
 
+        # When user is sending a generator we need to trust it's a valid example
+        generator_types = (types.GeneratorType, Dataset) if Dataset is not None else (types.GeneratorType,)
+        if isinstance(inputs, generator_types):
+            return inputs
+
         # Normalize inputs
         if isinstance(inputs, dict):
             inputs = [inputs]
@@ -245,12 +254,18 @@ class QuestionAnsweringPipeline(ChunkPipeline):
         """
 
         # Convert inputs to features
+
         examples = self._args_parser(*args, **kwargs)
-        if len(examples) == 1:
+        if isinstance(examples, (list, tuple)) and len(examples) == 1:
             return super().__call__(examples[0], **kwargs)
         return super().__call__(examples, **kwargs)
 
     def preprocess(self, example, padding="do_not_pad", doc_stride=None, max_question_len=64, max_seq_len=None):
+        # XXX: This is specal, args_parser will not handle anything generator or dataset like
+        # For those we expect user to send a simple valid example either directly as a SquadExample or simple dict.
+        # So we still need a little sanitation here.
+        if isinstance(example, dict):
+            example = SquadExample(None, example["question"], example["context"], None, None, None)
 
         if max_seq_len is None:
             max_seq_len = min(self.tokenizer.model_max_length, 384)

tests/pipelines/test_pipelines_question_answering.py

@@ -125,6 +125,18 @@ class QAPipelineTests(unittest.TestCase, metaclass=PipelineTestCaseMeta):
 
         self.assertEqual(nested_simplify(outputs), {"score": 0.01, "start": 0, "end": 11, "answer": "HuggingFace"})
 
+    @require_torch
+    def test_small_model_pt_iterator(self):
+        # https://github.com/huggingface/transformers/issues/18510
+        pipe = pipeline(model="sshleifer/tiny-distilbert-base-cased-distilled-squad", batch_size=16, framework="pt")
+
+        def data():
+            for i in range(10):
+                yield {"question": "Where was HuggingFace founded ?", "context": "HuggingFace was founded in Paris."}
+
+        for outputs in pipe(data()):
+            self.assertEqual(nested_simplify(outputs), {"score": 0.01, "start": 0, "end": 11, "answer": "HuggingFace"})
+
     @require_torch
     def test_small_model_pt_softmax_trick(self):
         question_answerer = pipeline(