Review feedback re: openai

Author: mwildehahn

docs/builtin-tools.md

@@ -291,6 +291,10 @@ assert isinstance(result.output, BinaryImage)
 
 _(This example is complete, it can be run "as is")_
 
+OpenAI Responses models also respect the `aspect_ratio` parameter. Because the OpenAI API only exposes discrete image sizes,
+PydanticAI maps `'1:1'` -> `1024x1024`, `'2:3'` -> `1024x1536`, and `'3:2'` -> `1536x1024`. Providing any other aspect ratio
+results in an error, and if you also set `size` it must match the computed value.
+
 To control the aspect ratio when using Gemini image models, include the `ImageGenerationTool` explicitly:
 
 ```py {title="image_generation_google_aspect_ratio.py"}
@@ -322,7 +326,7 @@ For more details, check the [API documentation][pydantic_ai.builtin_tools.ImageG
 | `partial_images` | ✅ | ❌ |
 | `quality` | ✅ | ❌ |
 | `size` | ✅ | ❌ |
-| `aspect_ratio` | ❌ | ✅ |
+| `aspect_ratio` | ✅ (1:1, 2:3, 3:2) | ✅ |
 
 ## URL Context Tool
 

pydantic_ai_slim/pydantic_ai/builtin_tools.py

@@ -264,6 +264,7 @@ class ImageGenerationTool(AbstractBuiltinTool):
     Supported by:
 
     * Google image-generation models (Gemini)
+    * OpenAI Responses (maps '1:1', '2:3', and '3:2' to supported sizes)
     """
 
     kind: str = 'image_generation'

pydantic_ai_slim/pydantic_ai/models/openai.py

@@ -18,7 +18,7 @@
 from .._run_context import RunContext
 from .._thinking_part import split_content_into_text_and_thinking
 from .._utils import guard_tool_call_id as _guard_tool_call_id, now_utc as _now_utc, number_to_datetime
-from ..builtin_tools import CodeExecutionTool, ImageGenerationTool, MCPServerTool, WebSearchTool
+from ..builtin_tools import CodeExecutionTool, ImageAspectRatio, ImageGenerationTool, MCPServerTool, WebSearchTool
 from ..exceptions import UserError
 from ..messages import (
     AudioUrl,
@@ -134,6 +134,36 @@
     'failed': 'error',
 }
 
+_OPENAI_ASPECT_RATIO_TO_SIZE: dict[ImageAspectRatio, Literal['1024x1024', '1024x1536', '1536x1024']] = {
+    '1:1': '1024x1024',
+    '2:3': '1024x1536',
+    '3:2': '1536x1024',
+}
+
+
+def _resolve_openai_image_generation_size(
+    tool: ImageGenerationTool,
+) -> Literal['auto', '1024x1024', '1024x1536', '1536x1024']:
+    """Map `ImageGenerationTool.aspect_ratio` to an OpenAI size string when provided."""
+    aspect_ratio = tool.aspect_ratio
+    if aspect_ratio is None:
+        return tool.size
+
+    mapped_size = _OPENAI_ASPECT_RATIO_TO_SIZE.get(aspect_ratio)
+    if mapped_size is None:
+        supported = ', '.join(_OPENAI_ASPECT_RATIO_TO_SIZE)
+        raise UserError(
+            f'OpenAI image generation only supports `aspect_ratio` values: {supported}. '
+            'Specify one of those values or omit `aspect_ratio`.'
+        )
+
+    if tool.size not in ('auto', mapped_size):
+        raise UserError(
+            '`ImageGenerationTool` cannot combine `aspect_ratio` with a conflicting `size` when using OpenAI.'
+        )
+
+    return mapped_size
+
 
 class OpenAIChatModelSettings(ModelSettings, total=False):
     """Settings used for an OpenAI model request."""
@@ -1298,6 +1328,7 @@ def _get_builtin_tools(self, model_request_parameters: ModelRequestParameters) -
                 tools.append(mcp_tool)
             elif isinstance(tool, ImageGenerationTool):  # pragma: no branch
                 has_image_generating_tool = True
+                size = _resolve_openai_image_generation_size(tool)
                 tools.append(
                     responses.tool_param.ImageGeneration(
                         type='image_generation',
@@ -1308,7 +1339,7 @@ def _get_builtin_tools(self, model_request_parameters: ModelRequestParameters) -
                         output_format=tool.output_format or 'png',
                         partial_images=tool.partial_images,
                         quality=tool.quality,
-                        size=tool.size,
+                        size=size,
                     )
                 )
             else:

tests/models/test_openai_responses.py

@@ -1,7 +1,7 @@
 import json
 import re
 from dataclasses import replace
-from typing import Any, cast
+from typing import Any, Literal, cast
 
 import pytest
 from inline_snapshot import snapshot
@@ -32,17 +32,19 @@
     ToolCallPartDelta,
     ToolReturnPart,
     UnexpectedModelBehavior,
+    UserError,
     UserPromptPart,
     capture_run_messages,
 )
 from pydantic_ai.agent import Agent
-from pydantic_ai.builtin_tools import CodeExecutionTool, MCPServerTool, WebSearchTool
+from pydantic_ai.builtin_tools import CodeExecutionTool, ImageAspectRatio, MCPServerTool, WebSearchTool
 from pydantic_ai.exceptions import ModelHTTPError, ModelRetry
 from pydantic_ai.messages import (
     BuiltinToolCallEvent,  # pyright: ignore[reportDeprecated]
     BuiltinToolResultEvent,  # pyright: ignore[reportDeprecated]
 )
 from pydantic_ai.models import ModelRequestParameters
+from pydantic_ai.models.openai import _resolve_openai_image_generation_size  # pyright: ignore[reportPrivateUsage]
 from pydantic_ai.output import NativeOutput, PromptedOutput, TextOutput, ToolOutput
 from pydantic_ai.profiles.openai import openai_model_profile
 from pydantic_ai.tools import ToolDefinition
@@ -124,6 +126,37 @@ async def test_openai_responses_image_detail_vendor_metadata(allow_model_request
     assert all(part['detail'] == 'high' for part in image_parts)
 
 
+@pytest.mark.parametrize(
+    ('aspect_ratio', 'explicit_size', 'expected_size'),
+    [
+        ('1:1', 'auto', '1024x1024'),
+        ('2:3', '1024x1536', '1024x1536'),
+        ('3:2', 'auto', '1536x1024'),
+    ],
+)
+def test_openai_responses_image_generation_tool_aspect_ratio_mapping(
+    aspect_ratio: ImageAspectRatio,
+    explicit_size: Literal['1024x1024', '1024x1536', '1536x1024', 'auto'],
+    expected_size: Literal['1024x1024', '1024x1536', '1536x1024'],
+) -> None:
+    tool = ImageGenerationTool(aspect_ratio=aspect_ratio, size=explicit_size)
+    assert _resolve_openai_image_generation_size(tool) == expected_size
+
+
+def test_openai_responses_image_generation_tool_aspect_ratio_invalid() -> None:
+    tool = ImageGenerationTool(aspect_ratio='16:9')
+
+    with pytest.raises(UserError, match='OpenAI image generation only supports `aspect_ratio` values'):
+        _resolve_openai_image_generation_size(tool)
+
+
+def test_openai_responses_image_generation_tool_aspect_ratio_conflicts_with_size() -> None:
+    tool = ImageGenerationTool(aspect_ratio='1:1', size='1536x1024')
+
+    with pytest.raises(UserError, match='cannot combine `aspect_ratio` with a conflicting `size`'):
+        _resolve_openai_image_generation_size(tool)
+
+
 async def test_openai_responses_model_simple_response_with_tool_call(allow_model_requests: None, openai_api_key: str):
     model = OpenAIResponsesModel('gpt-4o', provider=OpenAIProvider(api_key=openai_api_key))