Error Calling Python code from .Net Core 6 web api

Question

I am using PythonNet 3.0.1 in my .Net Core 6C# project. Need is to call a .py file and process a csv and read the results back in C#. Have installed Python 3.11.4 on my machine as well as pandas library.

Now when I call the Api Code, it gives an error whenever I try to call the Api method more than once.

I have added a finally block with the following statement: PythonEngine.Shutdown()

The exception logged on console is:

System.NotSupportedException: BinaryFormatter serialization and deserialization are disabled within this application. See https://aka.ms/binaryformatter for more information.

at System.Runtime.Serialization.Formatters.Binary.BinaryFormatter.Serialize(Stream serializationStream, Object graph)

at Python.Runtime.RuntimeData.Stash()

at Python.Runtime.Runtime.Shutdown()

at Python.Runtime.PythonEngine.Shutdown()

How do I fix this error and ensure that the Api can be called more than once?

here is the Code I have in the C# class:

string fileLoc = AppDomain.CurrentDomain.BaseDirectory;
         try
        {
            Runtime.PythonDLL = "python311.dll";
            // Initialize the Python engine
            PythonEngine.Initialize();
            using (Py.GIL())
            {
                dynamic module = Py.Import("PythonSampleIronPython");
                dynamic result = module.calculator.xl2determination(fileLoc);
            }
            return new Audit();
        }
        catch (Exception err)
        {
            _logger.LogError("Unable to evaluate model", err);
            throw new Exception("Unable to evaluate model", err);
        }
        finally{
            PythonEngine.Shutdown();
        }

I did not find much help using Pythonnet. So appreciate any help from people using Pythonnet with C#

Here is the Python Code saved in file "PythonSampleIronPython.py".

class calculator: def add(x, y): return x + y def increment(x): x += 1 return x

Answer 1

I got this to work by intializing the PythonEngine on startup in Program.cs:

Environment.SetEnvironmentVariable("PYTHONNET_PYDLL", "path to python dll");
PythonEngine.PythonHome = "Path to Python installation";
PythonEngine.Initialize();
PythonEngine.BeginAllowThreads();

Then you can test it by using something like this:

using (Py.GIL())
{
    PythonEngine.Exec("print('Hello from Python')")
}

This solution doesn't require you to call PrintEngine.Shutdown() since it's running for the lifecycle of the application.

Using the github solution provided in the other answer:

I created a new class NoopFormatter that inherits from IFormatter:

using System.Runtime.Serialization;

namespace YourNameSpace;

public class NoopFormatter : IFormatter
{
    public object Deserialize(Stream s) => throw new NotImplementedException();

    public void Serialize(Stream s, object o) { }

    public SerializationBinder Binder { get; set; }
    public StreamingContext Context { get; set; }
    public ISurrogateSelector SurrogateSelector { get; set; }
}

Then in my class where I'm using the Python.Runtime I added this line before PythonEngine.Initialize()

Python.Runtime.RuntimeData.FormatterType = typeof(NoopFormatter);

This allowed PrintEngine.ShutDown() to execute without throwing the BinaryFormatter serialization exception.

Note: Depending on the use of threading in your application you may need to include PythonEngine.BeginAllowThreads() after you call PythonEngine.Initialize(); This fixed the issue of it locking up on using (Py.GIL()) when hitting the code a second time.