pythonnet · koubaa · Mar 29, 2020 · Apr 14, 2020 · Apr 23, 2020
diff --git a/src/FunctionCodec.cs b/src/FunctionCodec.cs
@@ -0,0 +1,185 @@
+using System;
+using System.Reflection;
+
+namespace Python.Runtime.Codecs
+{
+    //converts python functions to C# actions
+    public class FunctionCodec : IPyObjectDecoder
+    {
+        private static int GetNumArgs(PyObject pyCallable)
+        {
+            var locals = new PyDict();
+            locals.SetItem("f", pyCallable);
+            using (Py.GIL())
+                PythonEngine.Exec(@"
+from inspect import signature
+try:
+    x = len(signature(f).parameters)
+except:
+    x = 0
+", null, locals.Handle);
+
+            var x = locals.GetItem("x");
+            return new PyInt(x).ToInt32();
+        }
+
+        private static int GetNumArgs(Type targetType)
+        {
+            MethodInfo invokeMethod = targetType.GetMethod("Invoke");
+            return invokeMethod.GetParameters().Length;
+        }
+
+        private static bool IsUnaryAction(Type targetType)
+        {
+            return targetType == typeof(Action);
+        }
+
+        private static bool IsVariadicObjectAction(Type targetType)
+        {
+            return targetType == typeof(Action<object[]>);
+        }
+
+        private static bool IsUnaryFunc(Type targetType)
+        {
+            return targetType == typeof(Func<object>);
+        }
+
+        private static bool IsVariadicObjectFunc(Type targetType)
+        {
+            return targetType == typeof(Func<object[], object>);
+        }
+
+        private static bool IsAction(Type targetType)
+        {
+            return IsUnaryAction(targetType) || IsVariadicObjectAction(targetType);
+        }
+
+        private static bool IsFunc(Type targetType)
+        {
+            return IsUnaryFunc(targetType) || IsVariadicObjectFunc(targetType);
+        }
+
+        private static bool IsCallable(Type targetType)
+        {
+            //Python.Runtime.ClassManager dtype
+            return targetType.IsSubclassOf(typeof(MulticastDelegate));
+        }
+
+        public static FunctionCodec Instance { get; } = new FunctionCodec();
+        public bool CanDecode(PyObject objectType, Type targetType)
+        {
+            //python object must be callable
+            if (!objectType.IsCallable()) return false;
+
+            //C# object must be callable
+            if (!IsCallable(targetType))
+                return false;
+
+            return true;
+        }
+
+        private static object ConvertUnaryAction(PyObject pyObj)
+        {
+            Func<object> func = (Func<object>)ConvertUnaryFunc(pyObj);
+            Action action = () => { func(); };
+            return (object)action;
+        }
+
+        private static object ConvertVariadicObjectAction(PyObject pyObj, int numArgs)
+        {
+            Func<object[], object> func = (Func<object[], object>)ConvertVariadicObjectFunc(pyObj, numArgs);
+            Action<object[]> action = (object[] args) => { func(args); };
+            return (object)action;
+        }
+
+        //TODO share code between ConvertUnaryFunc and ConvertVariadicObjectFunc
+        private static object ConvertUnaryFunc(PyObject pyObj)
+        {
+            var pyAction = new PyObject(pyObj.Handle);
+            Func<object> func = () =>
+            {
+                var pyArgs = new PyObject[0];
+                using (Py.GIL())
+                {
+                    var pyResult = pyAction.Invoke(pyArgs);
+                    return pyResult.AsManagedObject(typeof(object));
+                }
+            };
+            return (object)func;
+        }
+
+        private static object ConvertVariadicObjectFunc(PyObject pyObj, int numArgs)
+        {
+            var pyAction = new PyObject(pyObj.Handle);
+            Func<object[], object> func = (object[] o) =>
+            {
+                var pyArgs = new PyObject[numArgs];
+                int i = 0;
+                foreach (object obj in o)
+                {
+                    pyArgs[i++] = obj.ToPython();
+                }
+
+                using (Py.GIL())
+                {
+                    var pyResult = pyAction.Invoke(pyArgs);
+                    return pyResult.AsManagedObject(typeof(object));
+                }
+            };
+            return (object)func;
+        }
+
+        public bool TryDecode<T>(PyObject pyObj, out T value)
+        {
+            value = default(T);
+            var tT = typeof(T);
+            if (!IsCallable(tT))
+                return false;
+
+            var numArgs = GetNumArgs(pyObj);
+            if (numArgs != GetNumArgs(tT))
+                return false;
+
+            if (IsAction(tT))
+            {
+                object actionObj = null;
+                if (numArgs == 0)
+                {
+                    actionObj = ConvertUnaryAction(pyObj);
+                }
+                else
+                {
+                    actionObj = ConvertVariadicObjectAction(pyObj, numArgs);
+                }
+
+                value = (T)actionObj;
+                return true;
+            }
+            else if (IsFunc(tT))
+            {
+
+                object funcObj = null;
+                if (numArgs == 0)
+                {
+                    funcObj = ConvertUnaryFunc(pyObj);
+                }
+                else
+                {
+                    funcObj = ConvertVariadicObjectFunc(pyObj, numArgs);
+                }
+
+                value = (T)funcObj;
+                return true;
+            }
+            else
+            {
+                return false;
+            }
+        }
+
+        public static void Register()
+        {
+            PyObjectConversions.RegisterDecoder(Instance);
+        }
+    }
+}
diff --git a/tests/FunctionCodecTests.cs b/tests/FunctionCodecTests.cs
@@ -0,0 +1,111 @@
+using System;
+using NUnit.Framework;
+
+namespace Python.Runtime.Codecs
+{
+    class FunctionCodecTests
+    {
+        [SetUp]
+        public void SetUp()
+        {
+            TestsRuntimeConfig.Ensure();
+            PythonEngine.Initialize();
+        }
+
+
+        [TearDown]
+        public void Dispose()
+        {
+            PythonEngine.Shutdown();
+        }
+
+        [Test]
+        public void FunctionAction()
+        {
+            var codec = FunctionCodec.Instance;
+
+            PyInt x = new PyInt(1);
+            PyDict y = new PyDict();
+            //non-callables can't be decoded into Action
+            Assert.IsFalse(codec.CanDecode(x, typeof(Action)));
+            Assert.IsFalse(codec.CanDecode(y, typeof(Action)));
+
+            var locals = new PyDict();
+            PythonEngine.Exec(@"
+def foo():
+    return 1
+def bar(a):
+    return 2
+", null, locals.Handle);
+
+            //foo, the function with no arguments
+            var fooFunc = locals.GetItem("foo");
+            Assert.IsFalse(codec.CanDecode(fooFunc, typeof(bool)));
+
+            //CanDecode does not work for variadic actions
+            //Assert.IsFalse(codec.CanDecode(fooFunc, typeof(Action<object[]>)));
+            Assert.IsTrue(codec.CanDecode(fooFunc, typeof(Action)));
+
+            Action fooAction;
+            Assert.IsTrue(codec.TryDecode(fooFunc, out fooAction));
+            Assert.DoesNotThrow(() => fooAction());
+
+            //bar, the function with an argument
+            var barFunc = locals.GetItem("bar");
+            Assert.IsFalse(codec.CanDecode(barFunc, typeof(bool)));
+            //Assert.IsFalse(codec.CanDecode(barFunc, typeof(Action)));
+            Assert.IsTrue(codec.CanDecode(barFunc, typeof(Action<object[]>)));
+
+            Action<object[]> barAction;
+            Assert.IsTrue(codec.TryDecode(barFunc, out barAction));
+            Assert.DoesNotThrow(() => barAction(new[] { (object)true }));
+        }
+
+        [Test]
+        public void FunctionFunc()
+        {
+            var codec = FunctionCodec.Instance;
+
+            PyInt x = new PyInt(1);
+            PyDict y = new PyDict();
+            //non-callables can't be decoded into Func
+            Assert.IsFalse(codec.CanDecode(x, typeof(Func<object>)));
+            Assert.IsFalse(codec.CanDecode(y, typeof(Func<object>)));
+
+            var locals = new PyDict();
+            PythonEngine.Exec(@"
+def foo():
+    return 1
+def bar(a):
+    return 2
+", null, locals.Handle);
+
+            //foo, the function with no arguments
+            var fooFunc = locals.GetItem("foo");
+            Assert.IsFalse(codec.CanDecode(fooFunc, typeof(bool)));
+
+            //CanDecode does not work for variadic actions
+            //Assert.IsFalse(codec.CanDecode(fooFunc, typeof(Func<object[], object>)));
+            Assert.IsTrue(codec.CanDecode(fooFunc, typeof(Func<object>)));
+
+            Func<object> foo;
+            Assert.IsTrue(codec.TryDecode(fooFunc, out foo));
+            object res1 = null;
+            Assert.DoesNotThrow(() => res1 = foo());
+            Assert.AreEqual(res1, 1);
+
+            //bar, the function with an argument
+            var barFunc = locals.GetItem("bar");
+            Assert.IsFalse(codec.CanDecode(barFunc, typeof(bool)));
+            //Assert.IsFalse(codec.CanDecode(barFunc, typeof(Func<object>)));
+            Assert.IsTrue(codec.CanDecode(barFunc, typeof(Func<object[], object>)));
+
+            Func<object[], object> bar;
+            Assert.IsTrue(codec.TryDecode(barFunc, out bar));
+            object res2 = null;
+            Assert.DoesNotThrow(() => res2 = bar(new[] { (object)true }));
+            Assert.AreEqual(res2, 2);
+        }
+
+    }
+}
diff --git a/tests/TestCallbacks.cs b/tests/TestCallbacks.cs
@@ -0,0 +1,98 @@
+using System;
+using NUnit.Framework;
+
+namespace Python.Runtime.Codecs
+{
+    public class TestCallbacks
+    {
+        [OneTimeSetUp]
+        public void SetUp()
+        {
+            TestsRuntimeConfig.Ensure();
+            PythonEngine.Initialize();
+        }
+
+        [OneTimeTearDown]
+        public void Dispose()
+        {
+            PythonEngine.Shutdown();
+        }
+
+        private class Callables
+        {
+            internal object CallFunction0(Func<object> func)
+            {
+                return func();
+            }
+
+            internal object CallFunction1(Func<object[], object> func, object arg)
+            {
+                return func(new[] { arg });
+            }
+
+            internal void CallAction0(Action func)
+            {
+                func();
+            }
+
+            internal void CallAction1(Action<object[]> func, object arg)
+            {
+                func(new[] { arg });
+            }
+        }
+
+        [Test]
+        public void TestPythonFunctionPassedIntoCLRMethod()
+        {
+            var locals = new PyDict();
+            PythonEngine.Exec(@"
+def ret_1():
+    return 1
+def str_len(a):
+    return len(a)
+", null, locals.Handle);
+
+            var ret1 = locals.GetItem("ret_1");
+            var strLen = locals.GetItem("str_len");
+
+            var callables = new Callables();
+
+            FunctionCodec.Register();
+
+            //ret1.  A function with no arguments that returns an integer
+            //it must be convertible to Action or Func<object> and not to Func<object, object>
+            {
+                Action result1 = null;
+                Func<object> result2 = null;
+                Assert.DoesNotThrow(() => { result1 = ret1.As<Action>(); });
+                Assert.DoesNotThrow(() => { result2 = ret1.As<Func<object>>(); });
+
+                Assert.DoesNotThrow(() => { callables.CallAction0((Action)result1); });
+                object ret2 = null;
+                Assert.DoesNotThrow(() => { ret2 = callables.CallFunction0((Func<object>)result2); });
+                Assert.AreEqual(ret2, 1);
+            }
+
+            //strLen.  A function that takes something with a __len__ and returns the result of that function
+            //It must be convertible to an Action<object[]> and Func<object[], object>) and not to an  Action or Func<object>
+            {
+                Action<object[]> result3 = null;
+                Func<object[], object> result4 = null;
+                Assert.DoesNotThrow(() => { result3 = strLen.As<Action<object[]>>(); });
+                Assert.DoesNotThrow(() => { result4 = strLen.As<Func<object[], object>>(); });
+
+                //try using both func and action to show you can get __len__ of a string but not an integer
+                Assert.Throws<PythonException>(() => { callables.CallAction1((Action<object[]>)result3, 2); });
+                Assert.DoesNotThrow(() => { callables.CallAction1((Action<object[]>)result3, "hello"); });
+                Assert.Throws<PythonException>(() => { callables.CallFunction1((Func<object[], object>)result4, 2); });
+
+                object ret2 = null;
+                Assert.DoesNotThrow(() => { ret2 = callables.CallFunction1((Func<object[], object>)result4, "hello"); });
+                Assert.AreEqual(ret2, 5);
+            }
+
+            //TODO - this function is internal inside of PythonNet.  It probably should be public.
+            //PyObjectConversions.Reset();
+        }
+    }
+}