Embedding Python into .NET

Warning

Because Python code running under Python.NET is inherently unverifiable, it runs totally under the radar of the security infrastructure of the CLR so you should restrict use of the Python assembly to trusted code.

The Python runtime assembly defines a number of public classes that provide a subset of the functionality provided by the Python C-API.

These classes include PyObject, PyList, PyDict, PyTuple, etc.

At a very high level, to embed Python in your application one will need to:

• Reference Python.Runtime.dll (e.g. via a PackageReference)

• Call PythonEngine.Initialize() to initialize Python

• Call PythonEngine.ImportModule(name) to import a module

The module you import can either start working with your managed app environment at the time its imported, or you can explicitly lookup and call objects in a module you import.

For general-purpose information on embedding Python in applications, use www.python.org or Google to find (C) examples. Because Python.NET is so closely integrated with the managed environment, one will generally be better off importing a module and deferring to Python code as early as possible rather than writing a lot of managed embedding code.

Note

Python is not free-threaded and uses a global interpreter lock to allow multi-threaded applications to interact safely with the Python interpreter. Much more information about this is available in the Python C-API documentation on the www.python.org Website.

When embedding Python in a managed application, one has to manage the GIL in just the same way you would when embedding Python in a C or C++ application.

Before interacting with any of the objects or APIs provided by the Python.Runtime namespace, calling code must have acquired the Python global interpreter lock by calling the PythonEngine.AcquireLock method. The only exception to this rule is the PythonEngine.Initialize method, which may be called at startup without having acquired the GIL.

When finished using Python APIs, managed code must call a corresponding PythonEngine.ReleaseLock to release the GIL and allow other threads to use Python.

A using statement may be used to acquire and release the GIL:

using (Py.GIL())
{
    PythonEngine.Exec("doStuff()");
}

The AcquireLock and ReleaseLock methods are thin wrappers over the unmanaged PyGILState_Ensure and PyGILState_Release functions from the Python API, and the documentation for those APIs applies to the managed versions.

Passing C# Objects to the Python Engine

This section demonstrates how to pass a C# object to the Python runtime. The example uses the following Person class:

public class Person
{
    public Person(string firstName, string lastName)
    {
        FirstName = firstName;
        LastName = lastName;
    }

    public string FirstName { get; set; }
    public string LastName { get; set; }
}

In order to pass a C# object to the Python runtime, it must be converted to a PyObject. This is done using the ToPython() extension method. The PyObject may then be set as a variable in a PyScope. Code executed from the scope will have access to the variable:

// create a person object
Person person = new Person("John", "Smith");

// acquire the GIL before using the Python interpreter
using (Py.GIL())
{
    // create a Python scope
    using (PyScope scope = Py.CreateScope())
    {
        // convert the Person object to a PyObject
        PyObject pyPerson = person.ToPython();

        // create a Python variable "person"
        scope.Set("person", pyPerson);

        // the person object may now be used in Python
        string code = "fullName = person.FirstName + ' ' + person.LastName";
        scope.Exec(code);
    }
}