Calling C# methods from IronPython

Question

I'm building a C# WebKit Web browser that can be automated with IronPython to aid with Quality Assurance testing. I'll be creating test plans with IronPython that will run a number of the browser methods, providing the arguments, and evaluating the results.

Most of the documentation for IronPython illustrates how to call IronPython methods with C#, yet I've figured out how to set arguments to a method, and how to retrieve a methods return values, but not from the same method. You'll note in the example below, I'm passing arguments to a method, which in turn is setting a class member variable, and then retrieving that value with another method.

Can anyone suggest a more elegant pattern?

using System;
using System.Windows.Forms;
using IronPython.Hosting;
using Microsoft.Scripting;
using Microsoft.Scripting.Hosting;

namespace PythonScripting.TestApp
{

 public partial class Form1 : Form
 {
   private ScriptEngine m_engine = Python.CreateEngine();
   private ScriptScope m_scope = null;

   //used to call funcs by Python that dont need to return vals
   delegate void VoidFunc(string val);

   public Form1()
   {
      InitializeComponent();
   }

   private void doSomething()
   {
       MessageBox.Show("Something Done", "TestApp Result");
   }

   private string _rslt = "";

   private string getSomething()
   {
      return _rslt;
   }

   private void setSomething(string val)
   {
       _rslt = val;
   }

   private void Form1_Load(object sender, EventArgs e)
   {
       m_scope = m_engine.CreateScope();

       Func<string> PyGetFunction = new Func<string>(getSomething);
       VoidFunc PySetFunction = new VoidFunc(setSomething);

       m_scope.SetVariable("txt", txtBoxTarget);
       m_scope.SetVariable("get_something", PyGetFunction);
       m_scope.SetVariable("set_something", PySetFunction);           
   }

   private void button1_Click(object sender, EventArgs e)
   {
       string code = comboBox1.Text.Trim();
       ScriptSource source = m_engine.CreateScriptSourceFromString(code, SourceCodeKind.SingleStatement);

       try
       {
          source.Execute(m_scope);
          Func<string> result = m_scope.GetVariable<Func<string>>("get_something");

          MessageBox.Show("Result: " + result(), "TestApp Result");
       }
       catch (Exception ue)
       {
           MessageBox.Show("Unrecognized Python Error\n\n" + ue.GetBaseException(), "Python Script Error");
       }
   }  
 }
}

What version of the framework are you targeting? Using dynamic here would make all of this trivial to do. — Jeff Mercado
– Jeff Mercado, Commented Nov 12, 2012 at 0:32
Thanks Jeff, I'm obv an IronPython noob- I'll look into this... — Gene Myers
– Gene Myers, Commented Nov 17, 2012 at 16:29
Understanding this code really helped me, for anyone interested: thinkingeek.com/2009/03/11/… — Gene Myers
– Gene Myers, Commented Nov 17, 2012 at 23:06

Jeff Mercado · Accepted Answer · 2012-11-17 22:35:53Z

7

Under normal circumstances, IronPython only has access to public classes and members on .Net types. You should be able to just set your object as a variable in the scope and access any of the public members on that object from your scripts. However the methods you have in your example are private so therefore you can't really access them. If you wish to be able to access them, you need to expose the non-public members somehow so you can manipulate them or use reflection.

A pattern you could try would be to add a method that would create a proxy for your object that would have all the methods you would want to expose. Then add that proxy object to your scope then use that proxy to call your methods.

public partial class MyForm : Form
{
    private readonly ScriptEngine m_engine;
    private readonly ScriptScope m_scope;

    public MyForm()
    {
        InitializeComponent();
        m_engine = Python.CreateEngine();

        dynamic scope = m_scope = m_engine.CreateScope();
        // add this form to the scope
        scope.form = this;
        // add the proxy to the scope
        scope.proxy = CreateProxy();
    }

    // public so accessible from a IronPython script
    public void ShowMessage(string message)
    {
        MessageBox.Show(message);
    }

    // private so not accessible from a IronPython script
    private int MyPrivateFunction()
    {
        MessageBox.Show("Called MyForm.MyPrivateFunction");
        return 42;
    }

    private object CreateProxy()
    {
        // let's expose all methods we want to access from a script
        dynamic proxy = new ExpandoObject();
        proxy.ShowMessage = new Action<string>(ShowMessage);
        proxy.MyPrivateFunction = new Func<int>(MyPrivateFunction);
        return proxy;
    }
}

With this, you can execute your scripts accessing your form through the form variable or the proxy through the proxy variable. For good measure, here's how you could easily access variables and other objects from the scope.

private void DoTests()
{
    // try to call the methods on the form or proxy objects
    var script = @"
form.ShowMessage('called form.ShowMessage')
# formFuncResult = form.MyPrivateFunction() # fail, MyPrivateFunction is not accessible
proxy.ShowMessage('called proxy.ShowMessage')
proxyFuncResult = proxy.MyPrivateFunction() # success, MyPrivateFunction on the proxy is accessible
";
    m_engine.Execute(script, m_scope);

    // access the scope through a dynamic variable
    dynamic scope = m_scope;

    // get the proxyFuncResult variable
    int proxyFuncResult = scope.proxyFuncResult;
    MessageBox.Show("proxyFuncResult variable: " + proxyFuncResult);

    // call the the function on the proxy directly
    int directResult = scope.proxy.MyPrivateFunction();
    MessageBox.Show("result of MyPrivateFunction: " + directResult);
}

answered Nov 17, 2012 at 22:35

Jeff Mercado

136k34 gold badges268 silver badges282 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Gene Myers Over a year ago

Thanks Jeff, I actually did change these to public between the time I posted this and when you replied just now. This great stuff. The proxy looks to be what I was looking for, yet I don't see how the form variable is used so I'll dig around a bit. Thanks again. -G

Jeff Mercado Over a year ago

If you look at the constructor in my example, I added a form variable to the scope which is a reference to this form object (which is from what I can tell the object you wanted to interact with). You'll also see that the proxy variable is set to the created proxy object. They were added just for the purpose of demonstrating how the script can access these objects.

Gene Myers Over a year ago

Jeff, thanks for this- I'm still pouring through your example- for anyone else wishing to get up to speed with the dynamic keyword and the ExpandoObject, this MSDN article lays a good foundation msdn.microsoft.com/en-us/magazine/gg598922.aspx

johv · Accepted Answer · 2012-11-11 22:12:42Z

3

I'm unsure of what you're trying to achieve, but how about this?

In C#:

m_scope.SetVariable("myAssembly", System.Reflection.Assembly.GetExecutingAssembly());

[...]

var result = (string) m_scope.GetVariable("theOutVar");

Then in the IronPython script:

import clr
clr.AddReference(myAssembly)
import MyNamespace
theOutVar = MyNamespace.MyClass.MyStaticMethod("hi")

Or perhaps like this?

In C#:

m_scope.SetVariable("theTestObject", myTestObj);

And in IronPython:

result = myTestObj.DoSomething("hi there", 10, false)

answered Nov 11, 2012 at 22:12

johv

4,6243 gold badges30 silver badges43 bronze badges

1 Comment

Gene Myers Over a year ago

What I was trying to do, precisely, was be able to call C# methods from an iron python script (setting the method parameters) yet have the result easily available in the C# application. My confusion was the correct syntax for using the GetVariable method. All I needed to do was return the method to a variable in IronPython like you illustrated above, result = GetSomething("my val") and call scope.GetVariable("result")

Collectives™ on Stack Overflow

Calling C# methods from IronPython

2 Answers 2

3 Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related