you saved my day. thx

Starting with Python.NET 3.0 you will also need to setRuntime.PythonDLL to the python dynamic library, otherwise you will getTypeInitializationException.

Starting with Python.NET 3.0 you will also need to setRuntime.PythonDLL to the python dynamic library, otherwise you will getTypeInitializationException.

thnx for the heads up!

How I got it working

*Python 3.8
*VS2022
*Target framework 4.7.2
*Platform Target x64 (note you must change this, you can't leave it on ANYCPU)
*Pythonnet 3.0.1 (via nuget)

    private static void setup_py_venv_003()    {        Runtime.PythonDLL = @"C:\Python38\python38.dll";        var pathToVirtualEnv = Path.GetFullPath(Path.Combine(Directory.GetCurrentDirectory(), @"..\..\..\venv"));        Console.WriteLine(pathToVirtualEnv);        Console.WriteLine(Runtime.PythonDLL);        Console.WriteLine(PythonEngine.Platform);        Console.WriteLine(PythonEngine.MinSupportedVersion);        Console.WriteLine(PythonEngine.MaxSupportedVersion);        Console.WriteLine(PythonEngine.BuildInfo);        Console.WriteLine(PythonEngine.PythonPath);        string additional = $"{pathToVirtualEnv};{pathToVirtualEnv}\\Lib\\site-packages;{pathToVirtualEnv}\\Lib";        PythonEngine.PythonPath = PythonEngine.PythonPath + ";" + additional;        Console.WriteLine(PythonEngine.PythonPath);        PythonEngine.Initialize();        PythonEngine.BeginAllowThreads();    }

So I am adding three parts on to the end of the existing python path

1. Root {pathToVirtualEnv}
2. Site Packages {pathToVirtualEnv}\Lib\site-packages
3. Lib folder {pathToVirtualEnv}\Lib

Output

C:\Users\sean\_CODE\_SMALL\PythonCore\venv----------C:\Python38\python38.dllwin324.74.11.2147483647.2147483647tags/v3.8.0:fa919fd, Oct 14 2019, 19:37:50C:\Python38\python38.zip;C:\Python38\Lib\;C:\Python38\DLLs\;C:\Users\sean\_CODE\_SMALL\PythonCore\ConsoleCshrp\bin\Debug----------C:\Python38\python38.zip;C:\Python38\Lib\;C:\Python38\DLLs\;C:\Users\sean\_CODE\_SMALL\PythonCore\ConsoleCshrp\bin\Debug;C:\Users\sean\_CODE\_SMALL\PythonCore\venv;C:\Users\sean\_CODE\_SMALL\PythonCore\venv\Lib\site-packages;C:\Users\sean\_CODE\_SMALL\PythonCore\venv\Lib----------

Then it goes on to run these successfully

 private static void run_some_tests()    {        using (Py.GIL())        {            dynamic np = Py.Import("numpy");            Console.WriteLine(np.cos(np.pi * 2));            dynamic sin = np.sin;            Console.WriteLine(sin(5));            double c = (double)(np.cos(5) + sin(5));            Console.WriteLine(c);            dynamic a = np.array(new List<float> { 1, 2, 3 });            Console.WriteLine(a.dtype);            dynamic b = np.array(new List<float> { 6, 5, 4 }, dtype: np.int32);            Console.WriteLine(b.dtype);            Console.WriteLine(a * b);            Console.ReadKey();        }    }

A bit silly, but note in your venv you obviously need to have installed numpy into your venv first.

I found, to use avenv, what finally worked for me, was a modified version ofthe documentation:

Runtime.PythonDLL = @"C:\Users\<username>\AppData\Local\Programs\Python\Python310\python310.dll";var pathToVirtualEnv = @"path\to\env";// be sure not to overwrite your existing "PATH" environmental variable.var path = Environment.GetEnvironmentVariable("PATH").TrimEnd(';');path = string.IsNullOrEmpty(path) ? pathToVirtualEnv : path + ";" + pathToVirtualEnv;Environment.SetEnvironmentVariable("PATH", path, EnvironmentVariableTarget.Process);Environment.SetEnvironmentVariable("PATH", pathToVirtualEnv, EnvironmentVariableTarget.Process);// Environment.SetEnvironmentVariable("PYTHONHOME", pathToVirtualEnv, EnvironmentVariableTarget.Process);Environment.SetEnvironmentVariable("PYTHONPATH", $"{pathToVirtualEnv}\\Lib\\site-packages;{pathToVirtualEnv}\\Lib", EnvironmentVariableTarget.Process);PythonEngine.Initialize();PythonEngine.PythonHome = pathToVirtualEnv;PythonEngine.PythonPath = Environment.GetEnvironmentVariable("PYTHONPATH", EnvironmentVariableTarget.Process);

Notice

1. Comment out:// Environment.SetEnvironmentVariable("PYTHONHOME", pathToVirtualEnv, EnvironmentVariableTarget.Process);
2. Then call:PythonEngine.Initialize(); beforePythonEngine

Not sure why yet.

I found, to use avenv, what finally worked for me, was a modified version ofthe documentation:

Runtime.PythonDLL = @"C:\Users\<username>\AppData\Local\Programs\Python\Python310\python310.dll";var pathToVirtualEnv = @"path\to\env";// be sure not to overwrite your existing "PATH" environmental variable.var path = Environment.GetEnvironmentVariable("PATH").TrimEnd(';');path = string.IsNullOrEmpty(path) ? pathToVirtualEnv : path + ";" + pathToVirtualEnv;Environment.SetEnvironmentVariable("PATH", path, EnvironmentVariableTarget.Process);Environment.SetEnvironmentVariable("PATH", pathToVirtualEnv, EnvironmentVariableTarget.Process);// Environment.SetEnvironmentVariable("PYTHONHOME", pathToVirtualEnv, EnvironmentVariableTarget.Process);Environment.SetEnvironmentVariable("PYTHONPATH", $"{pathToVirtualEnv}\\Lib\\site-packages;{pathToVirtualEnv}\\Lib", EnvironmentVariableTarget.Process);PythonEngine.Initialize();PythonEngine.PythonHome = pathToVirtualEnv;PythonEngine.PythonPath = Environment.GetEnvironmentVariable("PYTHONPATH", EnvironmentVariableTarget.Process);

Notice

1. Comment out:// Environment.SetEnvironmentVariable("PYTHONHOME", pathToVirtualEnv, EnvironmentVariableTarget.Process);
2. Then call:PythonEngine.Initialize(); beforePythonEngine

Not sure why yet.

Just moving the PythonEngine.Initialize(); before PythonEngine worked for me, thanks.

If anyone has some nice examples (this repo lacks them) would be great to see them./

On Windows the provided example fromhttps://github.com/pythonnet/pythonnet/wiki/Using-Python.NET-with-Virtual-Environments worked just fine (no need to call PythonEngine.Initialize(); before setting PythonHome and PythonPath). However, I can not get this working on Linux (Ubuntu 20.04). If someone has any advices, please add a comment below. Thanks.

@helldanno Instead of ";" and "\" on Windows, I think Linux uses ":" and "/".

Maybe change code to use System.IO.Path.DirectorySeparatorChar instead of "\" backslash

For environment variable delimiter find it with below. There might be a better way.
string environmentVarDelimiter = (Environment.OSVersion.Platform == PlatformID.Win32NT) ? ";" : ":";