René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"SetNoSiteFlag is ignored on Windows unless another PythonEngine call precedes it","articleBody":"### Environment\r\n\r\n-   Pythonnet version: Self-built from commit ec65efe30dfb1249c31c42f56623936782db0fde 8/11/2021\r\n-   Python version: 3.8.10\r\n-   Operating System: Windows 10 Pro 20H2 19042.1110\r\n-   .NET Runtime: .NET Core 3.1\r\n\r\n### Details\r\n\r\n-   Describe what you were trying to get done.\r\n\r\n    I am trying to disable automatic site run in order to setup a custom virtualenv path.\r\n\r\n-   What commands did you run to trigger this issue? If you can provide a\r\n    [Minimal, Complete, and Verifiable example](http://stackoverflow.com/help/mcve)\r\n    this will help us understand the issue.\r\n\r\n```\r\nusing System;\r\nusing System.Collections.Generic;\r\nusing Python.Runtime;\r\n\r\n\r\nnamespace TestPythonnet\r\n{\r\n    class Program\r\n    {\r\n        static void Main(string[] args)\r\n        {\r\n\r\n            // my base environment\r\n            // also added this to top of PATH in project settings\r\n            var pathToBaseEnv = @\"C:\\Users\\myuser\\AppData\\Local\\Programs\\Python\\Python38\";\r\n            Environment.SetEnvironmentVariable(\"PYTHONNET_PYVER\", \"3.8\", EnvironmentVariableTarget.Process);\r\n\r\n            // this call has no effect\r\n            PythonEngine.SetNoSiteFlag();\r\n            // if you swap this call with previous line, it will work\r\n            PythonEngine.PythonHome = pathToBaseEnv;\r\n\r\n            PythonEngine.Initialize();\r\n            using (Py.GIL())\r\n            {\r\n                Console.WriteLine($\"sys.executable: {sys.executable}\");\r\n                Console.WriteLine($\"sys.prefix: {sys.prefix}\");\r\n                Console.WriteLine($\"sys.base_prefix: {sys.base_prefix}\");\r\n                Console.WriteLine($\"sys.exec_prefix: {sys.exec_prefix}\");\r\n                Console.WriteLine($\"sys.base_exec_prefix: {sys.base_exec_prefix}\");\r\n                Console.WriteLine(\"sys.path:\");\r\n                foreach (var p in sys.path)\r\n                {\r\n                    Console.WriteLine(p);\r\n                }\r\n                Console.WriteLine();\r\n            }\r\n\r\n            PythonEngine.Shutdown();\r\n        }\r\n    }\r\n}\r\n```\r\nResult:\r\n```\r\nsys.executable: C:\\Users\\myuser\\source\\repos\\TestPythonnet\\TestPythonnet\\bin\\Debug\\netcoreapp3.1\\TestPythonnet.exe\r\nsys.prefix: C:\\Users\\myuser\\AppData\\Local\\Programs\\Python\\Python38\r\nsys.base_prefix: C:\\Users\\myuser\\AppData\\Local\\Programs\\Python\\Python38\r\nsys.exec_prefix: C:\\Users\\myuser\\AppData\\Local\\Programs\\Python\\Python38\r\nsys.base_exec_prefix: C:\\Users\\myuser\\AppData\\Local\\Programs\\Python\\Python38\r\nsys.path:\r\nC:\\Users\\myuser\\OneDrive\\Documents\\Python Scripts\r\nC:\\Users\\myuser\\AppData\\Local\\Programs\\Python\\Python38\\python38.zip\r\nC:\\Users\\myuser\\AppData\\Local\\Programs\\Python\\Python38\\DLLs\r\nC:\\Users\\myuser\\AppData\\Local\\Programs\\Python\\Python38\\lib\r\nC:\\Users\\myuser\\source\\repos\\TestPythonnet\\TestPythonnet\\bin\\Debug\\netcoreapp3.1\r\nC:\\Users\\myuser\\AppData\\Local\\Programs\\Python\\Python38\r\nC:\\Users\\myuser\\AppData\\Local\\Programs\\Python\\Python38\\lib\\site-packages\r\nC:\\Program Files\\dotnet\\shared\\Microsoft.NETCore.App\\3.1.18\\\r\n```\r\nThe site packages are still added.\r\n\r\nIf you swap order of `PythonEngine.SetNoSiteFlag();` and `PythonEngine.PythonHome = pathToBaseEnv;`, it works\r\n```\r\nsys.executable: C:\\Users\\myuser\\source\\repos\\TestPythonnet\\TestPythonnet\\bin\\Debug\\netcoreapp3.1\\TestPythonnet.exe\r\nsys.prefix: C:\\Users\\myuser\\AppData\\Local\\Programs\\Python\\Python38\r\nsys.base_prefix: C:\\Users\\myuser\\AppData\\Local\\Programs\\Python\\Python38\r\nsys.exec_prefix: C:\\Users\\myuser\\AppData\\Local\\Programs\\Python\\Python38\r\nsys.base_exec_prefix: C:\\Users\\myuser\\AppData\\Local\\Programs\\Python\\Python38\r\nsys.path:\r\nC:\\Users\\myuser\\OneDrive\\Documents\\Python Scripts\r\nC:\\Users\\myuser\\AppData\\Local\\Programs\\Python\\Python38\\python38.zip\r\nC:\\Users\\myuser\\AppData\\Local\\Programs\\Python\\Python38\\DLLs\r\nC:\\Users\\myuser\\AppData\\Local\\Programs\\Python\\Python38\\lib\r\nC:\\Users\\myuser\\source\\repos\\TestPythonnet\\TestPythonnet\\bin\\Debug\\netcoreapp3.1\r\nC:\\Program Files\\dotnet\\shared\\Microsoft.NETCore.App\\3.1.18\\\r\n```\r\nNo site folders added to the path.\r\n\r\nIn fact, one can workaround the issue by adding any access to the PythonEngine API which uses the DLL before setting the flag, e.g.\r\n```\r\nvar version = PythonEngine.Version;\r\nPythonEngine.SetNoSiteFlag();\r\n```\r\n\r\n\r\nThe root cause appears to be that the reference count on the DLL is sent to zero after setting Py_NoSiteFlag, so the DLL is unloaded and reloaded by the Delegate class with the original value of Py_NoSiteFlag=0.\r\n\r\nSnip from Python.Runtime.Runtime (runtime.cs) with my added comments.\r\n```\r\ninternal static void SetNoSiteFlag()\r\n        {\r\n            var loader = LibraryLoader.Instance;\r\n            IntPtr dllLocal = IntPtr.Zero;\r\n            if (_PythonDll != \"__Internal\")\r\n            {\r\n                dllLocal = loader.Load(_PythonDll);\r\n                if (dllLocal == IntPtr.Zero)\r\n                {\r\n                    throw new Exception($\"Cannot load {_PythonDll}\");\r\n                }\r\n            }\r\n            try\r\n            {\r\n                Py_NoSiteFlag = loader.GetFunction(dllLocal, \"Py_NoSiteFlag\");\r\n                Marshal.WriteInt32(Py_NoSiteFlag, 1); // This works, I can Marshal.ReadInt32 with Immediate window in Debug and get 1\r\n            }\r\n            finally\r\n            {\r\n                if (dllLocal != IntPtr.Zero)\r\n                {\r\n                    loader.Free(dllLocal); // if nobody else loaded _PythonDll, it will potentially get unloaded here :-(\r\n                }\r\n            }\r\n        }\r\n```\r\n\r\n-   If there was a crash, please include the traceback here.\r\n\r\nN/A\r\n","author":{"url":"https://github.com/bpdavis86","@type":"Person","name":"bpdavis86"},"datePublished":"2021-08-12T17:06:18.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":1},"url":"https://github.com/1517/pythonnet/issues/1517"}