Don't prematurely handle event streams

This removes event streams from the generated deser methods, as they
aren't handled there. They will eventually be handled by the protocol
python implementation on a higher level. This also removes the
attempt at handling them as if they were a blob stream, as they are
currently handled elsewhere.

Author: JordonPhillips

codegen/smithy-python-codegen/src/main/java/software/amazon/smithy/python/codegen/StructureGenerator.java

@@ -389,27 +389,41 @@ private void generateDeserializeMethod() {
         writer.putContext("schema", schemaSymbol);
 
         // TODO: either formalize deserialize_kwargs or remove it when http serde is converted
-        writer.write("""
-                @classmethod
-                def deserialize(cls, deserializer: ShapeDeserializer) -> Self:
-                    return cls(**cls.deserialize_kwargs(deserializer))
-
-                @classmethod
-                def deserialize_kwargs(cls, deserializer: ShapeDeserializer) -> dict[str, Any]:
-                    kwargs: dict[str, Any] = {}
-
-                    def _consumer(schema: Schema, de: ShapeDeserializer) -> None:
-                        match schema.expect_member_index():
-                            ${C|}
-                            case _:
-                                logger.debug(f"Unexpected member schema: {schema}")
-
-                    deserializer.read_struct($T, consumer=_consumer)
-                    return kwargs
-
-                """,
-                writer.consumer(w -> deserializeMembers(shape.members())),
-                schemaSymbol);
+        var deserializeableMembers = filterMembers();
+        if (deserializeableMembers.isEmpty()) {
+            writer.write("""
+                    @classmethod
+                    def deserialize(cls, deserializer: ShapeDeserializer) -> Self:
+                        return cls()
+
+                    @classmethod
+                    def deserialize_kwargs(cls, deserializer: ShapeDeserializer) -> dict[str, Any]:
+                        return {}
+
+                    """);
+        } else {
+            writer.write("""
+                    @classmethod
+                    def deserialize(cls, deserializer: ShapeDeserializer) -> Self:
+                        return cls(**cls.deserialize_kwargs(deserializer))
+
+                    @classmethod
+                    def deserialize_kwargs(cls, deserializer: ShapeDeserializer) -> dict[str, Any]:
+                        kwargs: dict[str, Any] = {}
+
+                        def _consumer(schema: Schema, de: ShapeDeserializer) -> None:
+                            match schema.expect_member_index():
+                                ${C|}
+                                case _:
+                                    logger.debug(f"Unexpected member schema: {schema}")
+
+                        deserializer.read_struct($T, consumer=_consumer)
+                        return kwargs
+
+                    """,
+                    writer.consumer(w -> deserializeMembers(filterMembers())),
+                    schemaSymbol);
+        }
         writer.popState();
     }
 

codegen/smithy-python-codegen/src/main/java/software/amazon/smithy/python/codegen/integration/RestJsonProtocolGenerator.java

@@ -314,10 +314,15 @@ protected void deserializePayloadBody(
 
         var symbolProvider = context.symbolProvider();
         var memberName = symbolProvider.toMemberName(payloadBinding.getMember());
+        var target = context.model().expectShape(payloadBinding.getMember().getTarget());
 
-        if (payloadBinding.getMember().getMemberTrait(context.model(), StreamingTrait.class).isPresent()) {
-            writer.addImport("smithy_core.aio.types", "AsyncBytesReader");
-            writer.write("kwargs[$S] = AsyncBytesReader(http_response.body)", memberName);
+        if (target.hasTrait(StreamingTrait.class)) {
+            // If the target is a union, nothing needs to be done here. The stream deserializer will
+            // take the response body directly and handle it.
+            if (target.isBlobShape()) {
+                writer.addImport("smithy_core.aio.types", "AsyncBytesReader");
+                writer.write("kwargs[$S] = AsyncBytesReader(http_response.body)", memberName);
+            }
             return;
         }
 
@@ -334,7 +339,6 @@ protected void deserializePayloadBody(
                     """);
         }
 
-        var target = context.model().expectShape(payloadBinding.getMember().getTarget());
         var deserializerSymbol = symbolProvider.toSymbol(target);
 
         writer.write("if body:").indent();