Clear pending Python error when a Try-style conversion fails

src/embed_tests/TestConverter.cs

@@ -513,6 +513,39 @@ class TestPythonModel(TestCSharpModel):
             Assert.AreEqual(shouldConvert, Converter.ToManaged(testPythonModelClass, type, out var result, setError: false));
             Assert.IsFalse(Exceptions.ErrorOccurred());
         }
+
+        [TestCase(true)]
+        [TestCase(false)]
+        public void RaisingIteratorFailsArrayConversion(bool setError)
+        {
+            using var _ = Py.GIL();
+
+            var module = PyModule.FromString("RaisingIteratorModule", @"
+def gen():
+    yield 1
+    raise ValueError('mid-iteration failure')
+");
+            using var generator = module.GetAttr("gen").Invoke();
+
+            // the conversion must fail rather than return a silently truncated array,
+            // and the raised error must only be left pending when setError is true
+            Assert.IsFalse(Converter.ToManaged(generator, typeof(int[]), out var result, setError));
+            Assert.IsNull(result);
+            Assert.AreEqual(setError, Exceptions.ErrorOccurred());
+            Exceptions.Clear();
+        }
+
+        [TestCase(true)]
+        [TestCase(false)]
+        public void OverflowConversionOnlyLeavesErrorWhenSettingErrors(bool setError)
+        {
+            using var _ = Py.GIL();
+
+            using var pyValue = new PyInt(300);
+            Assert.IsFalse(Converter.ToManaged(pyValue, typeof(byte), out var _, setError));
+            Assert.AreEqual(setError, Exceptions.ErrorOccurred());
+            Exceptions.Clear();
+        }
     }
 
     public interface IGetList

src/embed_tests/TestPyObject.cs

@@ -102,6 +102,40 @@ public void InheritedMethodsAutoacquireGIL()
         {
             PythonEngine.Exec("from System import String\nString.Format('{0},{1}', 1, 2)");
         }
+
+        [Test]
+        public void FailedTryAsDoesNotLeavePythonErrorSet()
+        {
+            using var _ = Py.GIL();
+
+            using var locals = new PyDict();
+            PythonEngine.Exec("def a_function(a, b): return a * b", null, locals);
+            using var pyObject = locals.GetItem("a_function");
+
+            Assert.IsFalse(pyObject.TryAs<int>(out var _));
+            Assert.IsFalse(Exceptions.ErrorOccurred());
+
+            Assert.IsFalse(pyObject.TryAsManagedObject(typeof(decimal), out var _));
+            Assert.IsFalse(Exceptions.ErrorOccurred());
+
+            // The thread state must be clean for subsequent unrelated Python calls
+            Assert.DoesNotThrow(() => PyModule.FromString("TryAsLeakCheck", "x = 1").Dispose());
+        }
+
+        [Test]
+        public void FailedAsManagedObjectRaisesWithConversionErrorAsCause()
+        {
+            using var _ = Py.GIL();
+
+            using var locals = new PyDict();
+            PythonEngine.Exec("def a_function(a, b): return a * b", null, locals);
+            using var pyObject = locals.GetItem("a_function");
+
+            var exception = Assert.Throws<InvalidCastException>(() => pyObject.AsManagedObject(typeof(int)));
+            Assert.IsNotNull(exception.InnerException);
+            StringAssert.Contains("int()", exception.InnerException.Message);
+            Assert.IsFalse(Exceptions.ErrorOccurred());
+        }
     }
 
     public class PyObjectTestMethods

src/perf_tests/Python.PerformanceTests.csproj

@@ -13,7 +13,7 @@
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
     </PackageReference>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.*" />
-    <PackageReference Include="quantconnect.pythonnet" Version="2.0.62" GeneratePathProperty="true">
+    <PackageReference Include="quantconnect.pythonnet" Version="2.0.63" GeneratePathProperty="true">
       <IncludeAssets>compile</IncludeAssets>
     </PackageReference>
   </ItemGroup>
@@ -25,7 +25,7 @@
   </Target>
 
   <Target Name="CopyBaseline" AfterTargets="Build">
-    <Copy SourceFiles="$(NuGetPackageRoot)quantconnect.pythonnet\2.0.62\lib\net10.0\Python.Runtime.dll" DestinationFolder="$(OutDir)baseline" />
+    <Copy SourceFiles="$(NuGetPackageRoot)quantconnect.pythonnet\2.0.63\lib\net10.0\Python.Runtime.dll" DestinationFolder="$(OutDir)baseline" />
   </Target>
 
   <Target Name="CopyNewBuild" AfterTargets="Build">

src/runtime/Converter.cs

@@ -507,6 +507,8 @@ internal static bool ToManagedValue(BorrowedReference value, Type obType,
                             catch
                             {
                                 // Failed to convert using implicit conversion,  must catch the error to stop program from exploding on Linux
+                                // Raised even when setError is false: MethodBinder.Invoke surfaces a pending
+                                // error as the binding failure reason instead of its generic no-match message
                                 Exceptions.RaiseTypeError($"Failed to implicitly convert {type} to {obType}");
                                 return false;
                             }
@@ -711,6 +713,8 @@ internal static bool ToManagedValue(BorrowedReference value, Type obType,
                         catch
                         {
                             // Failed to convert using implicit conversion,  must catch the error to stop program from exploding on Linux
+                            // Raised even when setError is false: MethodBinder.Invoke surfaces a pending
+                            // error as the binding failure reason instead of its generic no-match message
                             Exceptions.RaiseTypeError($"Failed to implicitly convert {result.GetType()} to {obType}");
                             return false;
                         }
@@ -1371,6 +1375,11 @@ internal static bool ToPrimitive(BorrowedReference value, Type obType, out objec
                 string tpName = Runtime.PyObject_GetTypeName(value);
                 Exceptions.SetError(Exceptions.TypeError, $"'{tpName}' value cannot be converted to {obType}");
             }
+            else
+            {
+                // a probing sub-path may have raised before jumping here
+                Exceptions.Clear();
+            }
             return false;
 
         overflow:
@@ -1379,6 +1388,10 @@ internal static bool ToPrimitive(BorrowedReference value, Type obType, out objec
             {
                 Exceptions.SetError(Exceptions.OverflowError, "value too large to convert");
             }
+            else
+            {
+                Exceptions.Clear();
+            }
             return false;
         }
 
@@ -1456,7 +1469,23 @@ private static bool ToArray(BorrowedReference value, Type obType, out object res
         private static bool ToList(BorrowedReference value, Type obType, out object result, bool setError)
         {
             var elementType = obType.GetGenericArguments()[0];
-            var IterObject = Runtime.PyObject_GetIter(value);
+            result = null;
+
+            using var IterObject = Runtime.PyObject_GetIter(value);
+            if (IterObject.IsNull())
+            {
+                if (setError)
+                {
+                    SetConversionError(value, obType);
+                }
+                else
+                {
+                    // PyObject_GetIter will have set an error
+                    Exceptions.Clear();
+                }
+                return false;
+            }
+
             result = MakeList(value, IterObject, obType, elementType, setError);
             return result != null;
         }
@@ -1499,17 +1528,41 @@ private static IList MakeList(BorrowedReference value, NewReference IterObject,
                     Exceptions.SetError(e);
                     SetConversionError(value, obType);
                 }
+                else
+                {
+                    // PySequence_Size may have raised (e.g. a broken __len__)
+                    Exceptions.Clear();
+                }
 
                 return null;
             }
 
             while (true)
             {
                 using var item = Runtime.PyIter_Next(IterObject.Borrow());
-                if (item.IsNull()) break;
+                if (item.IsNull())
+                {
+                    if (Exceptions.ErrorOccurred())
+                    {
+                        // the iterator raised mid-iteration: the conversion failed,
+                        // don't return a silently truncated list
+                        if (!setError)
+                        {
+                            Exceptions.Clear();
+                        }
+                        return null;
+                    }
+                    break;
+                }
 
                 if (!Converter.ToManaged(item.Borrow(), elementType, out var obj, setError))
                 {
+                    // some element conversion paths raise even when setError is false
+                    // (e.g. failed implicit operators, deleted types)
+                    if (!setError)
+                    {
+                        Exceptions.Clear();
+                    }
                     return null;
                 }
 

src/runtime/Properties/AssemblyInfo.cs

@@ -4,5 +4,5 @@
 [assembly: InternalsVisibleTo("Python.EmbeddingTest, PublicKey=00240000048000009400000006020000002400005253413100040000110000005ffd8f49fb44ab0641b3fd8d55e749f716e6dd901032295db641eb98ee46063cbe0d4a1d121ef0bc2af95f8a7438d7a80a3531316e6b75c2dae92fb05a99f03bf7e0c03980e1c3cfb74ba690aca2f3339ef329313bcc5dccced125a4ffdc4531dcef914602cd5878dc5fbb4d4c73ddfbc133f840231343e013762884d6143189")]
 [assembly: InternalsVisibleTo("Python.Test, PublicKey=00240000048000009400000006020000002400005253413100040000110000005ffd8f49fb44ab0641b3fd8d55e749f716e6dd901032295db641eb98ee46063cbe0d4a1d121ef0bc2af95f8a7438d7a80a3531316e6b75c2dae92fb05a99f03bf7e0c03980e1c3cfb74ba690aca2f3339ef329313bcc5dccced125a4ffdc4531dcef914602cd5878dc5fbb4d4c73ddfbc133f840231343e013762884d6143189")]
 
-[assembly: AssemblyVersion("2.0.62")]
-[assembly: AssemblyFileVersion("2.0.62")]
+[assembly: AssemblyVersion("2.0.63")]
+[assembly: AssemblyFileVersion("2.0.63")]

src/runtime/Python.Runtime.csproj

@@ -5,7 +5,7 @@
     <RootNamespace>Python.Runtime</RootNamespace>
     <AssemblyName>Python.Runtime</AssemblyName>
     <PackageId>QuantConnect.pythonnet</PackageId>
-    <Version>2.0.62</Version>
+    <Version>2.0.63</Version>
     <GenerateAssemblyInfo>false</GenerateAssemblyInfo>
     <PackageLicenseFile>LICENSE</PackageLicenseFile>
     <RepositoryUrl>https://github.com/pythonnet/pythonnet</RepositoryUrl>

src/runtime/PythonTypes/PyObject.cs

@@ -169,7 +169,7 @@ public static PyObject FromManagedObject(object ob)
         /// </remarks>
         public object? AsManagedObject(Type t)
         {
-            if (!TryAsManagedObject(t, out var result))
+            if (!Converter.ToManaged(obj, t, out var result, setError: true))
             {
                 throw new InvalidCastException("cannot convert object to target type",
                     PythonException.FetchCurrentOrNull(out _));
@@ -188,7 +188,15 @@ public static PyObject FromManagedObject(object ob)
         /// </summary>
         public bool TryAsManagedObject(Type t, out object? result)
         {
-            return Converter.ToManaged(obj, t, out result, true);
+            if (Converter.ToManaged(obj, t, out result, setError: false))
+            {
+                return true;
+            }
+            // A failed Try-conversion must not leave a Python error pending on the
+            // thread: the caller only sees the boolean, so a stale error indicator
+            // would surface from an unrelated later call on this thread.
+            Exceptions.Clear();
+            return false;
         }
 
         /// <summary>