pythonnet · lostmsu · Jun 26, 2019 · Aug 23, 2019 · Aug 26, 2019
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -10,6 +10,7 @@ This document follows the conventions laid out in [Keep a CHANGELOG][].
 ### Added
 
 -   Added automatic NuGet package generation in appveyor and local builds
+-   Added IGetAttr and ISetAttr, so that .NET classes could override __getattr__ and __setattr__
 
 ### Changed
 

diff --git a/src/embed_tests/Python.EmbeddingTest.csproj b/src/embed_tests/Python.EmbeddingTest.csproj
@@ -89,6 +89,7 @@
     <Compile Include="TestDomainReload.cs" />
     <Compile Include="TestExample.cs" />
     <Compile Include="TestFinalizer.cs" />
+    <Compile Include="TestInstanceWrapping.cs" />
     <Compile Include="TestPyAnsiString.cs" />
     <Compile Include="TestPyFloat.cs" />
     <Compile Include="TestPyInt.cs" />

diff --git a/src/embed_tests/TestInstanceWrapping.cs b/src/embed_tests/TestInstanceWrapping.cs
@@ -0,0 +1,50 @@
+using NUnit.Framework;
+using Python.Runtime;
+using Python.Runtime.Slots;
+
+namespace Python.EmbeddingTest {
+    public class TestInstanceWrapping {
+        [Test]
+        public void GetAttrCanBeOverriden() {
+            var overloaded = new Overloaded();
+            using (Py.GIL()) {
+                var o = overloaded.ToPython();
+                dynamic getNonexistingAttr = PythonEngine.Eval("lambda o: o.non_existing_attr");
+                string nonexistentAttrValue = getNonexistingAttr(o);
+                Assert.AreEqual(GetAttrFallbackValue, nonexistentAttrValue);
+            }
+        }
+
+        [Test]
+        public void SetAttrCanBeOverriden() {
+            var overloaded = new Overloaded();
+            using (Py.GIL())
+            using (var scope = Py.CreateScope()) {
+                var o = overloaded.ToPython();
+                scope.Set(nameof(o), o);
+                scope.Exec($"{nameof(o)}.non_existing_attr = 42");
+                Assert.AreEqual(42, overloaded.Value);
+            }
+        }
+
+        const string GetAttrFallbackValue = "undefined";
+
+        class Base {}
+        class Derived: Base { }
+
+        class Overloaded: Derived, IGetAttr, ISetAttr
+        {
+            public int Value { get; private set; }
+
+            public bool TryGetAttr(string name, out PyObject value) {
+                value = GetAttrFallbackValue.ToPython();
+                return true;
+            }
+
+            public bool TrySetAttr(string name, PyObject value) {
+                this.Value = value.As<int>();
+                return true;
+            }
+        }
+    }
+}
diff --git a/src/runtime/Python.Runtime.csproj b/src/runtime/Python.Runtime.csproj
@@ -22,19 +22,19 @@
   </PropertyGroup>
   <!--We can relax binding to platform because code references no any platform dependent assemblies-->
   <!--This will allows to use any build of this assebly as a compile ref assebly-->
-  <!--<PropertyGroup Condition=" '$(Platform)' == 'x86'">
-    <PlatformTarget>x86</PlatformTarget>
-  </PropertyGroup>
-  <PropertyGroup Condition=" '$(Platform)' == 'x64'">
-    <PlatformTarget>x64</PlatformTarget>
+  <!--<PropertyGroup Condition=" '$(Platform)' == 'x86'">
+    <PlatformTarget>x86</PlatformTarget>
+  </PropertyGroup>
+  <PropertyGroup Condition=" '$(Platform)' == 'x64'">
+    <PlatformTarget>x64</PlatformTarget>
   </PropertyGroup>-->
   <PropertyGroup Condition=" '$(Configuration)' == 'ReleaseMono'">
     <DefineConstants Condition="'$(DefineConstants)' == ''">PYTHON2;PYTHON27;UCS4</DefineConstants>
     <Optimize>true</Optimize>
     <DebugType>pdbonly</DebugType>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)' == 'ReleaseMonoPY3'">
-    <DefineConstants Condition="'$(DefineConstants)' == ''">PYTHON3;PYTHON37;UCS4</DefineConstants>
+    <DefineConstants Condition="'$(DefineConstants)' == ''">PYTHON3;PYTHON37;UCS4</DefineConstants>
     <Optimize>true</Optimize>
     <DebugType>pdbonly</DebugType>
   </PropertyGroup>
@@ -46,7 +46,7 @@
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)' == 'DebugMonoPY3'">
     <DebugSymbols>true</DebugSymbols>
-    <DefineConstants Condition="'$(DefineConstants)' == ''">PYTHON3;PYTHON37;UCS4;TRACE;DEBUG</DefineConstants>
+    <DefineConstants Condition="'$(DefineConstants)' == ''">PYTHON3;PYTHON37;UCS4;TRACE;DEBUG</DefineConstants>
     <Optimize>false</Optimize>
     <DebugType>full</DebugType>
   </PropertyGroup>
@@ -56,7 +56,7 @@
     <DebugType>pdbonly</DebugType>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)' == 'ReleaseWinPY3'">
-    <DefineConstants Condition="'$(DefineConstants)' == ''">PYTHON3;PYTHON37;UCS2</DefineConstants>
+    <DefineConstants Condition="'$(DefineConstants)' == ''">PYTHON3;PYTHON37;UCS2</DefineConstants>
     <Optimize>true</Optimize>
     <DebugType>pdbonly</DebugType>
   </PropertyGroup>
@@ -68,7 +68,7 @@
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)' == 'DebugWinPY3'">
     <DebugSymbols>true</DebugSymbols>
-    <DefineConstants Condition="'$(DefineConstants)' == ''">PYTHON3;PYTHON37;UCS2;TRACE;DEBUG</DefineConstants>
+    <DefineConstants Condition="'$(DefineConstants)' == ''">PYTHON3;PYTHON37;UCS2;TRACE;DEBUG</DefineConstants>
     <Optimize>false</Optimize>
     <DebugType>full</DebugType>
   </PropertyGroup>
@@ -137,11 +137,12 @@
     <Compile Include="pythonexception.cs" />
     <Compile Include="pytuple.cs" />
     <Compile Include="runtime.cs" />
+    <Compile Include="slots.cs" />
     <Compile Include="typemanager.cs" />
     <Compile Include="typemethod.cs" />
     <Compile Include="Util.cs" />
-    <Compile Include="platform\Types.cs" />
-    <Compile Include="platform\LibraryLoader.cs" />
+    <Compile Include="platform\Types.cs" />
+    <Compile Include="platform\LibraryLoader.cs" />
   </ItemGroup>
   <ItemGroup Condition=" '$(PythonInteropFile)' != '' ">
     <Compile Include="$(PythonInteropFile)" />
@@ -151,7 +152,7 @@
     <Compile Include="interop34.cs" />
     <Compile Include="interop35.cs" />
     <Compile Include="interop36.cs" />
-    <Compile Include="interop37.cs" />
+    <Compile Include="interop37.cs" />
   </ItemGroup>
   <ItemGroup>
     <None Include="..\pythonnet.snk" />
@@ -170,4 +171,4 @@
     <Copy SourceFiles="$(TargetAssembly)" DestinationFolder="$(PythonBuildDir)" />
     <!--Copy SourceFiles="$(TargetAssemblyPdb)" Condition="Exists('$(TargetAssemblyPdb)')" DestinationFolder="$(PythonBuildDir)" /-->
   </Target>
-</Project>
+</Project>
diff --git a/src/runtime/runtime.cs b/src/runtime/runtime.cs
@@ -103,7 +103,7 @@ public class Runtime
         internal static object IsFinalizingLock = new object();
         internal static bool IsFinalizing;
 
-        internal static bool Is32Bit = IntPtr.Size == 4;
+        internal static readonly bool Is32Bit = IntPtr.Size == 4;
 
         // .NET core: System.Runtime.InteropServices.RuntimeInformation.IsOSPlatform(OSPlatform.Windows)
         internal static bool IsWindows = Environment.OSVersion.Platform == PlatformID.Win32NT;
@@ -562,6 +562,14 @@ internal static unsafe void XIncref(IntPtr op)
 #endif
         }
 
+        /// <summary>
+        /// Increase Python's ref counter for the given object, and return the object back.
+        /// </summary>
+        internal static IntPtr SelfIncRef(IntPtr op) {
+            XIncref(op);
+            return op;
+        }
+
         internal static unsafe void XDecref(IntPtr op)
         {
 #if PYTHON_WITH_PYDEBUG || NETSTANDARD

diff --git a/src/runtime/slots.cs b/src/runtime/slots.cs
@@ -0,0 +1,47 @@
+using System;
+
+namespace Python.Runtime.Slots
+{
+    /// <summary>
+    /// Implement this interface to override Python's __getattr__ for your class
+    /// </summary>
+    public interface IGetAttr {
+        bool TryGetAttr(string name, out PyObject value);
+    }
+
+    /// <summary>
+    /// Implement this interface to override Python's __setattr__ for your class
+    /// </summary>
+    public interface ISetAttr {
+        bool TrySetAttr(string name, PyObject value);
+    }
+
+    static class SlotOverrides {
+        public static IntPtr tp_getattro(IntPtr ob, IntPtr key) {
+            IntPtr genericResult = Runtime.PyObject_GenericGetAttr(ob, key);
+            if (genericResult != IntPtr.Zero || !Runtime.PyString_Check(key)) {
+                return genericResult;
+            }
+
+            Exceptions.Clear();
+
+            var self = (IGetAttr)((CLRObject)ManagedType.GetManagedObject(ob)).inst;
+            string attr = Runtime.GetManagedString(key);
+            return self.TryGetAttr(attr, out var value)
+                ? Runtime.SelfIncRef(value.Handle)
+                : Runtime.PyObject_GenericGetAttr(ob, key);
+        }
+
+        public static int tp_setattro(IntPtr ob, IntPtr key, IntPtr val) {
+            if (!Runtime.PyString_Check(key)) {
+                return Runtime.PyObject_GenericSetAttr(ob, key, val);
+            }
+
+            var self = (ISetAttr)((CLRObject)ManagedType.GetManagedObject(ob)).inst;
+            string attr = Runtime.GetManagedString(key);
+            return self.TrySetAttr(attr, new PyObject(Runtime.SelfIncRef(val)))
+                ? 0
+                : Runtime.PyObject_GenericSetAttr(ob, key, val);
+        }
+    }
+}
diff --git a/src/runtime/typemanager.cs b/src/runtime/typemanager.cs
@@ -4,10 +4,10 @@
 using System.Reflection;
 using System.Runtime.InteropServices;
 using Python.Runtime.Platform;
+using Python.Runtime.Slots;
 
 namespace Python.Runtime
 {
-
     /// <summary>
     /// The TypeManager class is responsible for building binary-compatible
     /// Python type objects that are implemented in managed code.
@@ -155,6 +155,14 @@ internal static IntPtr CreateType(ManagedType impl, Type clrType)
 
             InitializeSlots(type, impl.GetType());
 
+            if (typeof(IGetAttr).IsAssignableFrom(clrType)) {
+                InitializeSlot(type, TypeOffset.tp_getattro, typeof(SlotOverrides).GetMethod(nameof(SlotOverrides.tp_getattro)));
+            }
+
+            if (typeof(ISetAttr).IsAssignableFrom(clrType)) {
+                InitializeSlot(type, TypeOffset.tp_setattro, typeof(SlotOverrides).GetMethod(nameof(SlotOverrides.tp_setattro)));
+            }
+
             if (base_ != IntPtr.Zero)
             {
                 Marshal.WriteIntPtr(type, TypeOffset.tp_base, base_);
@@ -766,6 +774,11 @@ static void InitializeSlot(IntPtr type, IntPtr slot, string name)
             Marshal.WriteIntPtr(type, offset, slot);
         }
 
+        static void InitializeSlot(IntPtr type, int slotOffset, MethodInfo method) {
+            IntPtr thunk = Interop.GetThunk(method);
+            Marshal.WriteIntPtr(type, slotOffset, thunk);
+        }
+
         /// <summary>
         /// Given a newly allocated Python type object and a managed Type that
         /// implements it, initialize any methods defined by the Type that need