begin to implement list codec

pythonnet · lostmsu · Feb 18, 2021 · Mar 10, 2020 · Mar 10, 2020 · Mar 11, 2020
commit b500aa1837bfb83d367e9fc0e2ca7e777e6b0bfa
diff --git a/src/embed_tests/Codecs.cs b/src/embed_tests/Codecs.cs
@@ -1,7 +1,7 @@
 namespace Python.EmbeddingTest {
     using System;
     using System.Collections.Generic;
-    using System.Text;
+    using System.Linq;
     using NUnit.Framework;
     using Python.Runtime;
     using Python.Runtime.Codecs;
@@ -82,6 +82,31 @@ static void TupleRoundtripGeneric<T, TTuple>() {
                 Assert.AreEqual(expected: tuple, actual: restored);
             }
         }
+
+        [Test]
+        public void ListCodecTest()
+        {
+            var codec = ListCodec.Instance;
+            var items = new List<PyObject>() { new PyInt(1), new PyInt(2), new PyInt(3) };
+
+            var x = new PyList(items.ToArray());
+            Assert.IsTrue(codec.CanDecode(x, typeof(List<int>)));
+            Assert.IsTrue(codec.CanDecode(x, typeof(IList<bool>)));
+            Assert.IsTrue(codec.CanDecode(x, typeof(System.Collections.IEnumerable)));
+            Assert.IsTrue(codec.CanDecode(x, typeof(IEnumerable<int>)));
+            Assert.IsTrue(codec.CanDecode(x, typeof(ICollection<float>)));
+            Assert.IsFalse(codec.CanDecode(x, typeof(bool)));
+
+            System.Collections.IEnumerable plainEnumerable = null;
+            Assert.DoesNotThrow(() => { codec.TryDecode<System.Collections.IEnumerable>(x, out plainEnumerable); });
+            Assert.IsNotNull(plainEnumerable);
+            IList<object> list = null;
+            list = plainEnumerable.Cast<object>().ToList();
+            Assert.AreEqual(list.Count, 3);
+            Assert.AreEqual(list[0], 1);
+            Assert.AreEqual(list[1], 2);
+            Assert.AreEqual(list[2], 3);
+        }
     }
 
     /// <summary>

diff --git a/src/runtime/Codecs/ListCodec.cs b/src/runtime/Codecs/ListCodec.cs
@@ -0,0 +1,101 @@
+using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace Python.Runtime.Codecs
+{
+    class ListCodec : IPyObjectDecoder
+    {
+        public bool CanDecode(PyObject objectType, Type targetType)
+        {
+            //first check if the PyObject is iterable.
+            IntPtr IterObject = Runtime.PyObject_GetIter(objectType.Handle);
+            if (IterObject == IntPtr.Zero)
+                return false;
+
+            //if it is a plain IEnumerable, we can decode it using sequence protocol.
+            if (targetType == typeof(System.Collections.IEnumerable))
+                return true;
+
+            //if its not a plain IEnumerable it must be a generic type
+            if (!targetType.IsGenericType) return false;
+
+            Predicate<Type> IsCLRSequence = (Type type) => {
+                return (type.GetGenericTypeDefinition() == typeof(IEnumerable<>) ||
+                        type.GetGenericTypeDefinition() == typeof(ICollection<>) ||
+                        type.GetGenericTypeDefinition() == typeof(IList<>));
+            };
+
+            if (IsCLRSequence(targetType))
+                return true;
+
+            //if it implements any of the standard C# collection interfaces, we can decode it.
+            foreach (Type itf in targetType.GetInterfaces())
+            {
+                if (IsCLRSequence(itf))
+                    return true;
+            }
+
+            //TODO objectType should implement the Sequence protocol to be convertible to ICollection
+            //     and the list protocol to be convertible to IList.  We should check for list first,
+            //     then collection, then enumerable
+
+
+            //if we get here we cannot decode it.
+            return false;
+        }
+
+        private class PyEnumerable : System.Collections.IEnumerable
+        {
+            PyObject iterObject;
+            internal PyEnumerable(PyObject pyObj)
+            {
+                iterObject = new PyObject(Runtime.PyObject_GetIter(pyObj.Handle));
+            }
+
+            public IEnumerator GetEnumerator()
+            {
+                IntPtr item;
+                while ((item = Runtime.PyIter_Next(iterObject.Handle)) != IntPtr.Zero)
+                {
+                    object obj = null;
+                    if (!Converter.ToManaged(item, typeof(object), out obj, true))
+                    {
+                        Runtime.XDecref(item);
+                        break;
+                    }
+
+                    Runtime.XDecref(item);
+                    yield return obj;
+                }
+            }
+        }
+
+        private object ToPlainEnumerable(PyObject pyObj)
+        {
+            return new PyEnumerable(pyObj);
+        }
+
+        public bool TryDecode<T>(PyObject pyObj, out T value)
+        {
+            object var = null;
+            //first see if T is a plan IEnumerable
+            if (typeof(T) == typeof(System.Collections.IEnumerable))
+            {
+                var = ToPlainEnumerable(pyObj);
+            }
+
+            value = (T)var;
+            return false;
+        }
+
+        public static ListCodec Instance { get; } = new ListCodec();
+
+        public static void Register()
+        {
+            PyObjectConversions.RegisterDecoder(Instance);
+        }
+    }
+}