Incorrectly using a non-generic type with type parameters now produce…

…s a helpful Python error instead of throwing NullReferenceException
pythonnet · lostmsu · Dec 18, 2020 · Dec 17, 2020 · Dec 17, 2020 · Dec 18, 2020
commit 0fe042c803840ad929b2f7733f09d8e2ee6e80e6
diff --git a/AUTHORS.md b/AUTHORS.md
@@ -60,6 +60,7 @@
 -   Sean Freitag ([@cowboygneox](https://github.com/cowboygneox))
 -   Serge Weinstock ([@sweinst](https://github.com/sweinst))
 -   Simon Mourier ([@smourier](https://github.com/smourier))
+-   Tom Minka ([@tminka](https://github.com/tminka))
 -   Viktoria Kovescses ([@vkovec](https://github.com/vkovec))
 -   Ville M. Vainio ([@vivainio](https://github.com/vivainio))
 -   Virgil Dupras ([@hsoft](https://github.com/hsoft))

diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -42,6 +42,7 @@ details about the cause of the failure
 -    Made it possible to use `__len__` also on `ICollection<>` interface objects
 -    Made it possible to call `ToString`, `GetHashCode`, and `GetType` on inteface objects
 -    Fixed objects returned by enumerating `PyObject` being disposed too soon
+-    Incorrectly using a non-generic type with type parameters now produces a helpful Python error instead of throwing NullReferenceException
 
 ### Removed
 

diff --git a/src/embed_tests/TestList.cs b/src/embed_tests/TestList.cs
@@ -0,0 +1,35 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Reflection;
+using System.Text;
+using NUnit.Framework;
+using Python.Runtime;
+
+namespace Python.EmbeddingTest
+{
+    public class TestList
+    {
+        [OneTimeSetUp]
+        public void SetUp()
+        {
+            PythonEngine.Initialize();
+        }
+
+        [OneTimeTearDown]
+        public void Dispose()
+        {
+            PythonEngine.Shutdown();
+        }
+
+        [Test]
+        public void MissingGenericTypeTest()
+        {
+            Assert.Throws<PythonException>(() =>
+            PythonEngine.Exec($@"
+from System.Collections import IList
+IList[bool]
+"));
+        }
+    }
+}
diff --git a/src/runtime/classbase.cs b/src/runtime/classbase.cs
@@ -54,7 +54,7 @@ public virtual IntPtr type_subscript(IntPtr idx)
                 return c.pyHandle;
             }
 
-            return Exceptions.RaiseTypeError("no type matches params");
+            return Exceptions.RaiseTypeError($"{type.Namespace}.{type.Name} does not accept {types.Length} generic parameters");
         }
 
         /// <summary>

diff --git a/src/runtime/genericutil.cs b/src/runtime/genericutil.cs
@@ -75,20 +75,27 @@ public static List<string> GetGenericBaseNames(string ns)
         }
 
         /// <summary>
-        /// xxx
+        /// Finds a generic type with the given number of generic parameters and the same name and namespace as <paramref name="t"/>.
         /// </summary>
         public static Type GenericForType(Type t, int paramCount)
         {
             return GenericByName(t.Namespace, t.Name, paramCount);
         }
 
+        /// <summary>
+        /// Finds a generic type in the given namespace with the given name and number of generic parameters.
+        /// </summary>
         public static Type GenericByName(string ns, string name, int paramCount)
         {
-            foreach (Type t in GenericsByName(ns, name))
+            var types = GenericsByName(ns, name);
+            if (types != null)
             {
-                if (t.GetGenericArguments().Length == paramCount)
+                foreach (Type t in types)
                 {
-                    return t;
+                    if (t.GetGenericArguments().Length == paramCount)
+                    {
+                        return t;
+                    }
                 }
             }
             return null;