Python.Net PythonEngine.Initialize() crashes application without throwing exception

Question

My application (C#, VS2017) previously targeted Python 3.5.1. I have updated the system to Python 3.7.1 and have this is causing PythonEngine.Initialize() to crash the application without throwing an exception.

One internet suggestion was to set the Python env in VS, however this causes VS2017 to close when opening Python/environments. I switched to VS2019 and encountered the same issue with the stripped down code here:

using System.Windows.Forms;
using Python.Runtime;
namespace WindowsFormsApp3
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            try
            {
                PythonEngine.Initialize();
            }
            catch (Exception e)
            {
                string ex = e.ToString();
            }
        }
    }
}

Python.Net was installed successfully using:

pip install pythonnet

bmiller · Accepted Answer · 2022-12-12 21:35:35Z

UPDATE Dec 2022

There are 2 optional environment strings you can use to locate the python dll.

PYTHONNET_PYDLL explicitly set the dll name
PYTHONNET_PYVER explicitly set just the version string part of the dll name

Compiling with WINDOWS, OSX or LINUX defined is not required anymore

Here's my PythonNet init function.

Note that running "pip install pythonnet" only installs the ability to load & use CLR types & assemblies from Python. To embed PythonNet in a C# app, you actually don't need to install pythonnet on the Python side.

This function uses some globals set at startup.

Program.PythonHome -- points to the Python root folder I'm using
Program.ScriptsDir -- my own app python scripts dir
Program.ApplicationName -- just my own app name

I also call PythonEngine.BeginAllowThreads(); as I'm calling from multiple threads.

    public static void InitPython(Microsoft.Extensions.Logging.ILogger logger)
    {
        string py_home = Program.PythonHome;
        string py_path = $"{py_home};";

        // will be different on linux/mac
        string[] py_paths = {"DLLs", "lib", "lib/site-packages", "lib/site-packages/win32"
                , "lib/site-packages/win32/lib", "lib/site-packages/Pythonwin" };

        foreach (string p in py_paths)
        {
            py_path += $"{py_home}/{p};";
        }

        try
        {
            PythonEngine.PythonPath = $"{Program.ScriptsDir};{py_path}";
            PythonEngine.PythonHome = Program.PythonHome;
            PythonEngine.ProgramName = Program.ApplicationName;
            PythonEngine.Initialize();
            PythonEngine.BeginAllowThreads();

            logger.LogInformation("Python Version: {v}, {dll}", PythonEngine.Version.Trim(), Runtime.PythonDLL);
            logger.LogInformation("Python Home: {home}", PythonEngine.PythonHome);
            logger.LogInformation("Python Path: {path}", PythonEngine.PythonPath);

        }
        catch (System.TypeInitializationException e)
        {
            throw new Exception($"FATAL, Unable to load Python, dll={Runtime.PythonDLL}", e);
        }
        catch (Exception e)
        {
            throw new Exception($"Python initialization Exception, {e.Message}", e);
        }

    }

Thanks so much for this I searched half a day for a clear exposition of what the initializer was looking for without luck. This provided the answer the others did not.

Learner · Accepted Answer · 2023-03-16 11:27:08Z

0

Check if python is installed in your machine.

answered Mar 16, 2023 at 11:27

Learner

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