Add IsNone and None static attribute for PyObject

src/CSnakes.Runtime/CPython/Init.cs

@@ -1,4 +1,5 @@
 using CSnakes.Runtime.Python;
+using CSnakes.Runtime.Python.Interns;
 using System.Diagnostics;
 using System.Reflection;
 using System.Runtime.InteropServices;
@@ -83,6 +84,7 @@ private void InitializeEmbeddedPython()
                 // Import builtins module
                 var builtinsMod = Import("builtins");
                 PyNone = GetAttr(builtinsMod, "None");
+                PyObject.none = new PyNoneObject();
                 Py_DecRef(builtinsMod);
             }
             PyEval_SaveThread();

src/CSnakes.Runtime/CPython/None.cs

@@ -1,4 +1,7 @@
-namespace CSnakes.Runtime.CPython;
+using CSnakes.Runtime.Python;
+using System.ComponentModel;
+
+namespace CSnakes.Runtime.CPython;
 
 internal unsafe partial class CPythonAPI
 {
@@ -10,7 +13,16 @@ internal unsafe partial class CPythonAPI
     /// <returns>A new reference to None. In newer versions of Python, None is immortal anyway.</returns>
     internal static nint GetNone()
     {
+        if (PyNone == IntPtr.Zero)
+        {
+            throw new InvalidOperationException("Python is not initialized. You cannot call this method outside of a Python Environment context.");
+        }
         Py_IncRefRaw(PyNone);
         return PyNone;
     }
+
+    internal static bool IsNone(PyObject o)
+    {
+        return PyNone == o.DangerousGetHandle();
+    }
 }

src/CSnakes.Runtime/PyObjectTypeConverter.cs

@@ -136,7 +136,8 @@ internal partial class PyObjectTypeConverter : TypeConverter
             ITuple t => ConvertFromTuple(context, culture, t),
             IEnumerable e => ConvertFromList(context, culture, e),
             BigInteger b => ConvertFromBigInteger(context, culture, b),
-            null => new PyObject(CPythonAPI.GetNone()),
+            PyObject pyObject => pyObject,
+            null => PyObject.None,
             _ => base.ConvertFrom(context, culture, value)
         };
 
@@ -179,7 +180,7 @@ private PyObject ToPython(object? o, ITypeDescriptorContext? context, CultureInf
     {
         if (o is null)
         {
-            return new PyObject(CPythonAPI.GetNone());
+            return PyObject.None;
         }
 
         var result = ConvertFrom(context, culture, o);

src/CSnakes.Runtime/Python/Interns/ImmortalPyObject.cs

@@ -0,0 +1,13 @@
+using CSnakes.Runtime.CPython;
+namespace CSnakes.Runtime.Python.Interns;
+
+internal class ImmortalPyObject(nint handle) : PyObject(handle)
+{
+    protected override bool ReleaseHandle() => true;
+
+
+    protected override void Dispose(bool disposing)
+    {
+        // I am immortal!!
+    }
+}

src/CSnakes.Runtime/Python/Interns/PyNoneObject.cs

@@ -0,0 +1,18 @@
+using CSnakes.Runtime.CPython;
+
+namespace CSnakes.Runtime.Python.Interns;
+
+internal sealed class PyNoneObject : ImmortalPyObject
+
+{
+    public PyNoneObject() : base(CPythonAPI.GetNone())
+    {
+    }
+
+    public override bool IsNone() => true;
+
+    public override string GetRepr() => ToString();
+
+    public override string ToString() => "None";
+
+}

src/CSnakes.Runtime/Python/PyObject.cs

@@ -11,6 +11,7 @@
 public class PyObject : SafeHandle
 {
     private static readonly TypeConverter td = TypeDescriptor.GetConverter(typeof(PyObject));
+    internal static PyObject? none;
 
     internal PyObject(IntPtr pyObject, bool ownsHandle = true) : base(pyObject, ownsHandle)
     {
@@ -97,7 +98,7 @@
     /// Get the type for the object.
     /// </summary>
     /// <returns>A new reference to the type field.</returns>
-    public PyObject GetPythonType()
+    public virtual PyObject GetPythonType()
     {
         RaiseOnPythonNotInitialized();
         using (GIL.Acquire())
@@ -111,7 +112,7 @@
     /// </summary>
     /// <param name="name"></param>
     /// <returns>Attribute object (new ref)</returns>
-    public PyObject GetAttr(string name)
+    public virtual PyObject GetAttr(string name)
     {
         RaiseOnPythonNotInitialized();
         using (GIL.Acquire())
@@ -120,7 +121,7 @@
         }
     }
 
-    public bool HasAttr(string name)
+    public virtual bool HasAttr(string name)
     {
         RaiseOnPythonNotInitialized();
         using (GIL.Acquire())
@@ -133,7 +134,7 @@
     /// Get the iterator for the object. This is equivalent to iter(obj) in Python.
     /// </summary>
     /// <returns>The iterator object (new ref)</returns>
-    public PyObject GetIter()
+    public virtual PyObject GetIter()
     {
         RaiseOnPythonNotInitialized();
         using (GIL.Acquire())
@@ -146,7 +147,7 @@
     /// Get the results of the repr() function on the object.
     /// </summary>
     /// <returns></returns>
-    public string GetRepr()
+    public virtual string GetRepr()
     {
         RaiseOnPythonNotInitialized();
         using (GIL.Acquire())
@@ -157,6 +158,15 @@
         }
     }
 
+    /// <summary>
+    /// Is the Python object None?
+    /// </summary>
+    /// <returns>true if None, else false</returns>
+    public virtual bool IsNone() => CPythonAPI.IsNone(this);
+
+
+    public static PyObject None { get; } = new PyNoneObject();
+
     /// <summary>
     /// Call the object. Equivalent to (__call__)(args)
     /// All arguments are treated as positional.
@@ -292,7 +302,7 @@
         using (GIL.Acquire())
         {
             return value is null ?
-                new PyObject(CPythonAPI.GetNone()) :
+                PyObject.None :
                 (PyObject?)td.ConvertFrom(value);
         }
     }

src/CSnakes/Reflection/MethodReflection.cs

@@ -51,6 +51,21 @@ public static MethodDefinition FromMethod(PythonFunctionDefinition function, str
             {
                 continue;
             }
+            bool needsConversion = true; // TODO: Skip .From for PyObject arguments. 
+            ExpressionSyntax rhs = IdentifierName(parameter.cSharpParameter.Identifier);
+            if (needsConversion)
+                rhs = 
+                    InvocationExpression(
+                        MemberAccessExpression(
+                            SyntaxKind.SimpleMemberAccessExpression,
+                            IdentifierName("PyObject"),
+                            IdentifierName("From")))
+                        .WithArgumentList(
+                            ArgumentList(
+                                SingletonSeparatedList(
+                                    Argument(
+                                        IdentifierName(parameter.cSharpParameter.Identifier)))));
+
             pythonConversionStatements.Add(
                 LocalDeclarationStatement(
                     VariableDeclaration(
@@ -63,16 +78,8 @@ public static MethodDefinition FromMethod(PythonFunctionDefinition function, str
                                 EqualsValueClause(
                                     PostfixUnaryExpression(
                                         SyntaxKind.SuppressNullableWarningExpression,
-                                        InvocationExpression(
-                                            MemberAccessExpression(
-                                                SyntaxKind.SimpleMemberAccessExpression,
-                                                IdentifierName("PyObject"),
-                                                IdentifierName("From")))
-                                            .WithArgumentList(
-                                                ArgumentList(
-                                                    SingletonSeparatedList(
-                                                        Argument(
-                                                            IdentifierName(parameter.cSharpParameter.Identifier)))))))))))
+                                        rhs
+                                        ))))))
                 .WithUsingKeyword(
                     Token(SyntaxKind.UsingKeyword)));
         }

src/CSnakes/Reflection/TypeReflection.cs

@@ -26,7 +26,7 @@ public static TypeSyntax AsPredefinedType(PythonTypeSpec pythonType)
                 "Optional" => AsPredefinedType(pythonType.Arguments[0]),
                 "Generator" => CreateGeneratorType(pythonType.Arguments[0], pythonType.Arguments[1], pythonType.Arguments[2]),
                 // Todo more types... see https://docs.python.org/3/library/stdtypes.html#standard-generic-classes
-                _ => SyntaxFactory.ParseTypeName("PyObject"),// TODO : Should be nullable?
+                _ => SyntaxFactory.ParseTypeName("PyObject"),
             };
         }
         return pythonType.Name switch
@@ -36,8 +36,7 @@ public static TypeSyntax AsPredefinedType(PythonTypeSpec pythonType)
             "float" => SyntaxFactory.PredefinedType(SyntaxFactory.Token(SyntaxKind.DoubleKeyword)),
             "bool" => SyntaxFactory.PredefinedType(SyntaxFactory.Token(SyntaxKind.BoolKeyword)),
             "bytes" => SyntaxFactory.ParseTypeName("byte[]"),
-            // Todo more types...
-            _ => SyntaxFactory.ParseTypeName("PyObject"),// TODO : Should be nullable?
+            _ => SyntaxFactory.ParseTypeName("PyObject"),
         };
     }
 

src/Integration.Tests/Integration.Tests.csproj

@@ -17,6 +17,7 @@
     <None Remove="python\test_false_returns.py" />
     <None Remove="python\test_generators.py" />
     <None Remove="python\test_keywords.py" />
+    <None Remove="python\test_none.py" />
     <None Remove="python\test_reserved.py" />
     <None Remove="python\test_tuples.py" />
   </ItemGroup>
@@ -49,6 +50,9 @@
     <AdditionalFiles Include="python\test_keywords.py">
       <CopyToOutputDirectory>Always</CopyToOutputDirectory>
     </AdditionalFiles>
+    <AdditionalFiles Include="python\test_none.py">
+      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+    </AdditionalFiles>
     <AdditionalFiles Include="python\test_reserved.py">
       <CopyToOutputDirectory>Always</CopyToOutputDirectory>
     </AdditionalFiles>

src/Integration.Tests/NoneTests.cs

@@ -0,0 +1,23 @@
+using CSnakes.Runtime.Python;
+
+namespace Integration.Tests;
+public class NoneTests : IntegrationTestBase
+{
+    [Fact]
+    public void TestReturnsNoneIsNone()
+    {
+        var mod = Env.TestNone();
+        using PyObject result = mod.ReturnsNone();
+        Assert.True(result.IsNone());
+    }
+
+    [Fact]
+    public void TestNullArgAsNone()
+    {
+        PyObject none = PyObject.None;
+        Assert.True(none.IsNone());
+        // Give to function
+        var mod = Env.TestNone();
+        Assert.True(mod.TestNoneResult(none));
+    }
+}

src/Integration.Tests/python/test_none.py

@@ -0,0 +1,5 @@
+def returns_none():
+    return None
+
+def test_none_result(arg) -> bool:
+    return arg is None