fix(types): preserve falsy parsed_output values

src/anthropic/types/beta/parsed_beta_message.py

@@ -89,6 +89,6 @@ class ParsedBetaMessage(BetaMessage, Generic[ResponseFormatT]):
     @property
     def parsed_output(self) -> Optional[ResponseFormatT]:
         for content in self.content:
-            if content.type == "text" and content.parsed_output:
+            if content.type == "text" and content.parsed_output is not None:
                 return content.parsed_output
         return None

src/anthropic/types/parsed_message.py

@@ -77,6 +77,6 @@ class ParsedMessage(Message, Generic[ResponseFormatT]):
     @property
     def parsed_output(self) -> Optional[ResponseFormatT]:
         for content in self.content:
-            if content.type == "text" and content.parsed_output:
+            if content.type == "text" and content.parsed_output is not None:
                 return content.parsed_output
         return None

tests/lib/streaming/fixtures/falsy_parsed_output_response.txt

@@ -0,0 +1,18 @@
+event: message_start
+data: {"type":"message_start","message":{"id":"msg_01FalsyParsedOutput0000001","type":"message","role":"assistant","content":[],"model":"claude-sonnet-5-5","stop_reason":null,"stop_sequence":null,"usage":{"input_tokens":10,"output_tokens":1}}}
+
+event: content_block_start
+data: {"type":"content_block_start","index":0,"content_block":{"type":"text","text":""}}
+
+event: content_block_delta
+data: {"type":"content_block_delta","index":0,"delta":{"type":"text_delta","text":"0"}}
+
+event: content_block_stop
+data: {"type":"content_block_stop","index":0}
+
+event: message_delta
+data: {"type":"message_delta","delta":{"stop_reason":"end_turn","stop_sequence":null},"usage":{"output_tokens":2}}
+
+event: message_stop
+data: {"type":"message_stop"}
+

tests/lib/streaming/test_messages.py

@@ -470,6 +470,24 @@ def test_message_delta_omitted_usage_keeps_message_start(self, respx_mock: MockR
         ) as stream:
             assert_message_delta_omitted_usage_response(stream.get_final_message())
 
+    @pytest.mark.skipif(PYDANTIC_V1, reason="structured outputs not supported with pydantic v1")
+    @pytest.mark.respx(base_url=base_url)
+    def test_falsy_parsed_output_is_preserved(self, respx_mock: MockRouter) -> None:
+        respx_mock.post("/v1/messages").mock(
+            return_value=httpx2.Response(200, content=get_response("falsy_parsed_output_response.txt"))
+        )
+
+        with sync_client.messages.stream(
+            max_tokens=1024,
+            messages=[{"role": "user", "content": "Answer with zero"}],
+            model="claude-sonnet-5-5",
+            output_format=int,
+        ) as stream:
+            message = stream.get_final_message()
+
+        # `None` means "not parsed"; zero is a parsed value.
+        assert message.parsed_output == 0
+
     @pytest.mark.respx(base_url=base_url)
     @pytest.mark.filterwarnings("error")
     def test_message_stop_event_serialization(self, respx_mock: MockRouter) -> None:
@@ -748,6 +766,25 @@ async def test_message_delta_omitted_usage_keeps_message_start(self, respx_mock:
         ) as stream:
             assert_message_delta_omitted_usage_response(await stream.get_final_message())
 
+    @pytest.mark.asyncio
+    @pytest.mark.skipif(PYDANTIC_V1, reason="structured outputs not supported with pydantic v1")
+    @pytest.mark.respx(base_url=base_url)
+    async def test_falsy_parsed_output_is_preserved(self, respx_mock: MockRouter) -> None:
+        respx_mock.post("/v1/messages").mock(
+            return_value=httpx2.Response(200, content=to_async_iter(get_response("falsy_parsed_output_response.txt")))
+        )
+
+        async with async_client.messages.stream(
+            max_tokens=1024,
+            messages=[{"role": "user", "content": "Answer with zero"}],
+            model="claude-sonnet-5-5",
+            output_format=int,
+        ) as stream:
+            message = await stream.get_final_message()
+
+        # `None` means "not parsed"; zero is a parsed value.
+        assert message.parsed_output == 0
+
     @pytest.mark.asyncio
     @pytest.mark.respx(base_url=base_url)
     @pytest.mark.filterwarnings("error")

tests/lib/streaming/test_parsed_content_blocks.py

@@ -12,7 +12,7 @@
 from anthropic._models import construct_type_unchecked
 from anthropic.types.beta import BetaFallbackBlock
 from anthropic.types.content_block import ContentBlock
-from anthropic.types.parsed_message import ParsedTextBlock, ParsedContentBlock
+from anthropic.types.parsed_message import ParsedMessage, ParsedTextBlock, ParsedContentBlock
 from anthropic.types.beta.beta_usage import BetaUsage
 from anthropic.lib.streaming._beta_messages import accumulate_event
 from anthropic.types.beta.beta_content_block import BetaContentBlock
@@ -119,3 +119,30 @@ def test_parsed_output_is_readable_but_not_dumped(block_type: Any) -> None:
         assert "parsed_output" not in copied.model_dump()
         assert "parsed_output" not in copied.to_dict()
         assert "parsed_output" not in json.loads(copied.to_json())
+
+
+@pytest.mark.parametrize(
+    "falsy",
+    [0, False, "", [], {}],
+    ids=["zero", "false", "empty_string", "empty_list", "empty_dict"],
+)
+@pytest.mark.parametrize(
+    "message_type",
+    [ParsedMessage, ParsedBetaMessage],
+    ids=["non-beta", "beta"],
+)
+def test_parsed_output_keeps_a_falsy_value(message_type: Any, falsy: Any) -> None:
+    message = message_type.construct(
+        id="msg_123",
+        type="message",
+        role="assistant",
+        model="claude-sonnet-4-5",
+        content=[{"type": "text", "text": "0"}],
+        stop_reason="end_turn",
+        stop_sequence=None,
+        usage={"input_tokens": 1, "output_tokens": 1},
+    )
+    message.content[0].parsed_output = falsy
+
+    # `None` means the block was not parsed; a parsed falsy value is still an output.
+    assert message.parsed_output == falsy