Refactor python engines api

src/DynamoPackages/PackageLoader.cs

@@ -267,7 +267,7 @@ private void TryLoadPackageIntoLibrary(Package package)
 
 
                 PythonServices.PythonEngineManager.Instance.
-                    LoadPythonEngine(package.LoadedAssemblies.Select(x => x.Assembly));
+                    LoadPythonEngine(Log, package.LoadedAssemblies.Select(x => x.Assembly));
 
                 Log($"Loaded Package {package.Name} {package.VersionName} from {package.RootDirectory}");
                 PackgeLoaded?.Invoke(package);

src/NodeServices/PythonServices.cs

@@ -111,12 +111,52 @@
         public static PythonEngineManager Instance { get { return lazy.Value; } }
         #endregion
 
-        //TODO see DYN-6550 when hiding/replacing this obsolete field.
+        /// <summary>
+        /// A readonly collection of all the loaded Python engines
+        /// </summary>
+        public ReadOnlyCollection<PythonEngine> PythonEngines => new ReadOnlyCollection<PythonEngine>(AvailableEngines);
+
         /// <summary>
         /// An observable collection of all the loaded Python engines
         /// </summary>
-        [Obsolete("AvailableEngines field will be replaced in a future Dynamo release.")]
-        public ObservableCollection<PythonEngine> AvailableEngines;
+        internal ObservableCollection<PythonEngine> AvailableEngines;
+
+        public delegate void PythonEngineChangedHandler(PythonEngine engine);
+
+        private Action<PythonEngine> customizeEngine;
+
+        /// <summary>
+        /// Use this function to customize Python engine initialization.
+        /// This function will be called only once on all existing or future python engines (on PythonEngineAdded).
+        /// </summary>
+        public Action<PythonEngine> CustomizeEngine
+        {
+            set
+            {
+                customizeEngine = value;
+                if (customizeEngine != null)
+                {
+                    try
+                    {
+                        foreach (var engine in AvailableEngines)
+                        {
+                            customizeEngine(engine);
+                        }
+                    }
+                    catch { }
+                }
+            }
+        }
+
+        /// <summary>
+        /// Event that is triggered for every new engine that is added.
+        /// </summary>
+        public static PythonEngineChangedHandler PythonEngineAdded;
+
+        /// <summary>
+        /// Event that is triggered for every engine that is removed.
+        /// </summary>
+        public static PythonEngineChangedHandler PythonEngineRemoved;
 
         #region Constant strings
 
@@ -132,16 +172,11 @@
 
         internal static string PythonEvaluatorSingletonInstance = "Instance";
 
-        internal static string IronPythonEvaluatorClass = "IronPythonEvaluator";
-        internal static string IronPythonEvaluationMethod = "EvaluateIronPythonScript";
-
         internal static string CPythonEvaluatorClass = "CPythonEvaluator";
         internal static string CPythonEvaluationMethod = "EvaluatePythonScript";
 
-        internal static string IronPythonAssemblyName = "DSIronPython";
         internal static string CPythonAssemblyName = "DSCPython";
 
-        internal static string IronPythonTypeName = IronPythonAssemblyName + "." + IronPythonEvaluatorClass;
         internal static string CPythonTypeName = CPythonAssemblyName + "." + CPythonEvaluatorClass;
 
         internal static string PythonInputMarshalerProperty = "InputMarshaler";
@@ -157,7 +192,7 @@
         private PythonEngineManager()
         {
             AvailableEngines = new ObservableCollection<PythonEngine>();
-
+            AvailableEngines.CollectionChanged += AvailableEngines_CollectionChanged;
             // We check only for the default python engine because it is the only one loaded by static references.
             // Other engines can only be loaded through package manager
             LoadDefaultPythonEngine(AppDomain.CurrentDomain.GetAssemblies().
@@ -166,6 +201,48 @@
             AppDomain.CurrentDomain.AssemblyLoad += new AssemblyLoadEventHandler((object sender, AssemblyLoadEventArgs args) => LoadDefaultPythonEngine(args.LoadedAssembly));
         }
 
+        private void AvailableEngines_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
+        {
+            if (e.Action == System.Collections.Specialized.NotifyCollectionChangedAction.Add)
+            {
+                for (var ii=0; ii< e.NewItems.Count; ii++)
+                {
+                    try
+                    {
+                        PythonEngineAdded?.Invoke(e.NewItems[ii] as PythonEngine);
+                    }
+                    catch(Exception ex)
+                    {
+                        Console.WriteLine("PythonEngineAdded event failed with error : " + ex.Message + Environment.NewLine + ex.StackTrace);
+                    }
+
+                    try
+                    {
+                        customizeEngine.Invoke(e.NewItems[ii] as PythonEngine);
+                    }
+                    catch (Exception ex)
+                    {
+                        Console.WriteLine("CustomizeEngine failed with error : " + ex.Message + Environment.NewLine + ex.StackTrace);
+                    }
+                }
+            }
+
+            if (e.Action == System.Collections.Specialized.NotifyCollectionChangedAction.Remove)
+            {
+                for (var ii = 0; ii < e.OldItems.Count; ii++)
+                {
+                    try
+                    {
+                        PythonEngineRemoved?.Invoke(e.OldItems[ii] as PythonEngine);
+                    }
+                    catch (Exception ex)
+                    {
+                        Console.WriteLine("PythonEngineRemoved event failed with error : " + ex.Message + Environment.NewLine + ex.StackTrace);
+                    }
+                }
+            }
+        }
+
         private void LoadDefaultPythonEngine(Assembly a)
         {
             if (a == null ||
@@ -180,7 +257,7 @@
             }
             catch (Exception e)
             {
-                System.Diagnostics.Debug.WriteLine($"Failed to load {CPythonAssemblyName} with error: {e.Message}");
+                Console.WriteLine($"Failed to load {CPythonAssemblyName} with error: {e.Message}");
             }
         }
 
@@ -189,16 +266,32 @@
             return AvailableEngines.FirstOrDefault(x => x.Name == name);
         }
 
-        // This method can throw exceptions.
-        internal void LoadPythonEngine(IEnumerable<Assembly> assemblies)
+        /// <summary>
+        /// Load Python Engines from an array of assemblies
+        /// </summary>
+        /// <param name="assemblies"></param>
+        internal void LoadPythonEngine(Action<string> logger, IEnumerable<Assembly> assemblies)
         {
             foreach (var a in assemblies)
             {
-                LoadPythonEngine(a);
+                try
+                {
+                    LoadPythonEngine(a);
+                }
+                catch(Exception e)
+                {
+                    logger?.Invoke("Failed when looking for PythonEngines with error: " + e.Message + Environment.NewLine + e.StackTrace);
+                }
             }
         }
 
-        // This method can throw exceptions.
+        /// <summary>
+        /// Load Python Engines from an assembly
+        /// </summary>
+        /// <param name="assembly"></param>
+        /// <exception cref="Exception"></exception>
+        /// Make this public to support custom loading of Python Engines (ex load in isolated alc on the python assembly side)
+        /// How to transition to Dynamo loading in isolated ALC ? 
         private void LoadPythonEngine(Assembly assembly)
         {
             if (assembly == null)