pythonnet - Python.NET

Python.NET is a package that gives Python programmers nearly seamless integration with the .NET Common Language Runtime (CLR) and provides a powerful application scripting tool for .NET developers. It allows Python code to interact with the CLR, and may also be used to embed Python into a .NET application.

Calling .NET code from Python

Python.NET allows CLR namespaces to be treated essentially as Python packages.

import clr
from System import String
from System.Collections import *

To load an assembly, use the AddReference function in the clr module:

import clr
clr.AddReference("System.Windows.Forms")
from System.Windows.Forms import Form

By default, Mono will be used on Linux and macOS, .NET Framework on Windows. For details on the loading of different runtimes, please refer to the documentation.

.NET Core

If .NET Core is installed in a default location or the dotnet CLI tool is on the PATH, loading it instead of the default (Mono/.NET Framework) runtime just requires setting either the environment variable PYTHONNET_RUNTIME=coreclr or calling pythonnet.load explicitly:

from pythonnet import load
load("coreclr")

import clr

Embedding Python in .NET

• You must set Runtime.PythonDLL property or PYTHONNET_PYDLL environment variable starting with version 3.0, otherwise you will receive BadPythonDllException (internal, derived from MissingMethodException) upon calling Initialize. Typical values are python38.dll (Windows), libpython3.8.dylib (Mac), libpython3.8.so (most other Unix-like operating systems).
• Then call PythonEngine.Initialize(). If you plan to use Python objects from multiple threads, also call PythonEngine.BeginAllowThreads().
• All calls to python should be inside a using (Py.GIL()) {/* Your code here */} block.
• Import python modules using dynamic mod = Py.Import("mod"), then you can call functions as normal, eg mod.func(args).
• Use mod.func(args, Py.kw("keywordargname", keywordargvalue)) or mod.func(args, keywordargname: keywordargvalue) to apply keyword arguments.
• All python objects should be declared as dynamic type.
• Mathematical operations involving python and literal/managed types must have the python object first, eg. np.pi * 2 works, 2 * np.pi doesn't.

Example

static void Main(string[] args)
{
    PythonEngine.Initialize();
    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();
    }
}

Output:

1.0
-0.958924274663
-0.6752620892
float64
int32
[  6.  10.  12.]

Resources

Information on installation, FAQ, troubleshooting, debugging, and projects using pythonnet can be found in the Wiki:

https://github.com/pythonnet/pythonnet/wiki

Mailing list

https://mail.python.org/mailman/listinfo/pythondotnet

Chat

https://gitter.im/pythonnet/pythonnet

.NET Foundation

This project is supported by the .NET Foundation.