feat: GenAI - Improved the exception messages when candidates, parts …

…or text are not available

Improved cases:

* Response has no Candidates
* Response Candidate Content has no Parts
* Response Candidate Content Part has no text

PiperOrigin-RevId: 628236405

tests/unit/vertexai/test_generative_models.py

@@ -497,6 +497,58 @@ def test_generate_content_streaming(self, generative_models: generative_models):
         for chunk in stream:
             assert chunk.text
 
+    @mock.patch.object(
+        target=prediction_service.PredictionServiceClient,
+        attribute="generate_content",
+        new=mock_generate_content,
+    )
+    @pytest.mark.parametrize(
+        "generative_models",
+        [generative_models, preview_generative_models],
+    )
+    def test_generate_content_response_accessor_errors(
+        self, generative_models: generative_models
+    ):
+        """Checks that the exception text contains response information."""
+        model = generative_models.GenerativeModel("gemini-pro")
+
+        # Case when response has no candidates
+        response1 = model.generate_content("Please block with block_reason=OTHER")
+
+        assert response1.prompt_feedback.block_reason.name == "OTHER"
+
+        with pytest.raises(ValueError) as e:
+            _ = response1.text
+        assert e.match("no candidates")
+        assert e.match("prompt_feedback")
+
+        # Case when response candidate content has no parts
+        response2 = model.generate_content("Please fail!")
+
+        with pytest.raises(ValueError) as e:
+            _ = response2.text
+        assert e.match("no parts")
+        assert e.match("finish_reason")
+
+        with pytest.raises(ValueError) as e:
+            _ = response2.candidates[0].text
+        assert e.match("no parts")
+        assert e.match("finish_reason")
+
+        # Case when response candidate content part has no text
+        weather_tool = generative_models.Tool(
+            function_declarations=[
+                generative_models.FunctionDeclaration.from_func(get_current_weather)
+            ],
+        )
+        response3 = model.generate_content(
+            "What's the weather like in Boston?", tools=[weather_tool]
+        )
+        with pytest.raises(ValueError) as e:
+            print(response3.text)
+        assert e.match("no text")
+        assert e.match("function_call")
+
     @mock.patch.object(
         target=prediction_service.PredictionServiceClient,
         attribute="generate_content",

vertexai/generative_models/_generative_models.py

@@ -17,6 +17,7 @@
 
 import copy
 import io
+import json
 import pathlib
 from typing import (
     Any,
@@ -1658,8 +1659,23 @@ def text(self) -> str:
                 " Use `response.candidate[i].text` to get text of a particular candidate."
             )
         if not self.candidates:
-            raise ValueError("Response has no candidates (and no text).")
-        return self.candidates[0].text
+            raise ValueError(
+                "Response has no candidates (and thus no text)."
+                " The response is likely blocked by the safety filters.\n"
+                "Response:\n"
+                + _dict_to_pretty_string(self.to_dict())
+            )
+        try:
+            return self.candidates[0].text
+        except (ValueError, AttributeError) as e:
+            # Enrich the error message with the whole Response.
+            # The Candidate object does not have full information.
+            raise ValueError(
+                "Cannot get the response text.\n"
+                f"{e}\n"
+                "Response:\n"
+                + _dict_to_pretty_string(self.to_dict())
+            ) from e
 
     @property
     def prompt_feedback(
@@ -1728,7 +1744,17 @@ def citation_metadata(self) -> gapic_content_types.CitationMetadata:
     # GenerationPart properties
     @property
     def text(self) -> str:
-        return self.content.text
+        try:
+            return self.content.text
+        except (ValueError, AttributeError) as e:
+            # Enrich the error message with the whole Candidate.
+            # The Content object does not have full information.
+            raise ValueError(
+                "Cannot get the Candidate text.\n"
+                f"{e}\n"
+                "Candidate:\n"
+                + _dict_to_pretty_string(self.to_dict())
+            ) from e
 
     @property
     def function_calls(self) -> Sequence[gapic_tool_types.FunctionCall]:
@@ -1799,7 +1825,12 @@ def text(self) -> str:
         if len(self.parts) > 1:
             raise ValueError("Multiple content parts are not supported.")
         if not self.parts:
-            raise AttributeError("Content has no parts.")
+            raise ValueError(
+                "Response candidate content has no parts (and thus no text)."
+                " The candidate is likely blocked by the safety filters.\n"
+                "Content:\n"
+                + _dict_to_pretty_string(self.to_dict())
+            )
         return self.parts[0].text
 
 
@@ -1886,7 +1917,11 @@ def to_dict(self) -> Dict[str, Any]:
     @property
     def text(self) -> str:
         if "text" not in self._raw_part:
-            raise AttributeError("Part has no text.")
+            raise AttributeError(
+                "Response candidate content part has no text.\n"
+                "Part:\n"
+                + _dict_to_pretty_string(self.to_dict())
+            )
         return self._raw_part.text
 
     @property
@@ -2188,6 +2223,11 @@ def _append_gapic_part(
         base_part._pb = copy.deepcopy(new_part._pb)
 
 
+def _dict_to_pretty_string(d: dict) -> str:
+    """Format dict as a pretty-printed JSON string."""
+    return json.dumps(d, indent=2)
+
+
 _FORMAT_TO_MIME_TYPE = {
     "png": "image/png",
     "jpeg": "image/jpeg",