Calling a C# library from python

Question

Anyone can share a working example on how to call a simple C# library (actually its WPF) from python code? (I have tried using IronPython and had too much trouble with unsupported CPython library my python code is using so I thought of trying the other way around and calling my C# code from Python).

Here is the example I was playing with:

using System.Runtime.InteropServices;
using System.EnterpriseServices;

namespace DataViewerLibrary
{
    public interface ISimpleProvider
    {
       [DispIdAttribute(0)]
       void Start();
    }

    [ComVisible(true)]
    [ClassInterface(ClassInterfaceType.None)]
    public class PlotData : ServicedComponent, ISimpleProvider
    {
       public void Start()
       {
          Plot plotter = new Plot();
          plotter.ShowDialog();
       }
    }
}

Plotter is a WPF windows that plots an Ellipse

I don't know how to call this code from my python all. Any suggestions?

Solution 1

It is actually pretty easy. Just use NuGet to add the "UnmanagedExports" package to your .Net project. See https://sites.google.com/site/robertgiesecke/Home/uploads/unmanagedexports for details.

You can then export directly, without having to do a COM layer. Here is the sample C# code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading.Tasks;
using RGiesecke.DllExport;

class Test
{
    [DllExport("add", CallingConvention = CallingConvention.Cdecl)]
    public static int TestExport(int left, int right)
    {
        return left + right;
    }
}

You can then load the dll and call the exposed methods in Python (works for 2.7)

import ctypes
a = ctypes.cdll.LoadLibrary(source)
a.add(3, 5)

Solution 2

Since your post is tagged IronPython, if you want to use the sample C# the following should work.

import clr
clr.AddReference('assembly name here')
from DataViewerLibrary import PlotData 

p = PlotData()
p.Start()

Solution 3

Python for .Net (pythonnet) may be a reasonable alternative to IronPython in your situation. https://github.com/pythonnet/pythonnet/blob/master/README.rst

From the site:

Note that this package does not implement Python as a first-class CLR language - it does not produce managed code (IL) from Python code. Rather, it is an integration of the CPython engine with the .NET runtime. This approach allows you to use use CLR services and continue to use existing Python code and C-based extensions while maintaining native execution speeds for Python code.

Also

Python for .NET uses the PYTHONPATH (sys.path) to look for assemblies to load, in addition to the usual application base and the GAC. To ensure that you can implicitly import an assembly, put the directory containing the assembly in sys.path.

This package still requires that you have a local CPython runtime on your machine. See the full Readme for more info https://github.com/pythonnet/pythonnet

Solution 4

This project has been developed for that exact purpose - use C# classes in regular Python

https://bitbucket.org/pydotnet/pydotnet/wiki/Home

All you need to do is to install either MSI or EGG into your CPython. PyDotnet is Python module, so the executable stays regular python.exe from your installation of Python or Anaconda. Supported both 32bit and 64bit.

Unlimited access to all C# classes, methods with output and ref parameters, generic classes and generic methods, extension methods, private members.

Overloaded assembly loader with customized mechanics for searching assemblies.

.NET runtime type information convertible to class object, which can be instantiated as any other class.

Special import mode designed especially for Python interactive shell, which allows you to discover available assemblies, namespaces, classes, methods, etc.

I'm waiting for feedback:)

View more solutions

Comments

[Vincent]

The exact same code works with the last releases of Python for .Net. It's good to know that both solutions (IronPython and CPython+PythonNet) work the same way.

[CodeMonkey]

Very cool if you're in control of the library. If not I imagine you can make a wrapper .dll with C-style calling convention.

[constructor]

I received next error: AttributeError: function 'add' not found

[constructor]

see important note: stackoverflow.com/questions/34417972/…

[Vinod Srivastav]

>>> import dotnet.seamless Traceback (most recent call last): File "<stdin>", line 1, in <module> File "C:\Program Files\Python35-32\lib\site-packages\dotnet_init_.py", line 21, in <module> import dotnet.moduleloader File "C:\Program Files\Python35-32\lib\site-packages\dotnet\moduleloader.py", line 24, in <module> from dotnet import PyDotnet as _dotnet ImportError: DLL load failed: The specified module could not be found.

[Yikang Luo]

Quick Solution Please rename boost_python3-vc141-mt-1_64.dll to boost_python3-vc150-mt-1_64.dll inside the sitepackages\dotnet. see this post for more detai: bitbucket.org/pydotnet/pydotnet/issues/26/…

[Contango]

If you see the error AttributeError: function 'add' not found in Python, it is because it will not work with Any CPU. To fix, set the build type to x32 or x64 (depending on your version of Python). Then point at the right .dll, e.g. in the x64\Release folder.

[manjuv]

I built my c# dll in x64. The dll has been created in two folders obj and bin. If i use the dll from bin I am getting clr exception "Exception has occurred: OSError [WinError -532462766] Windows Error 0xe0434352" If i use the dll from obj I dont get OSError but AttributeError: function 'add' not found error.

[RGD2]

bit bucket link is a 404 at this time

[RGD2]

It is on pypi - but there it lacks a reference to numpy, so it works if pip install numpy before pip install pydotnet (in cmd as administrator, with just python3.9.1 installed).

[Eric Mutta]

Project is now on github.