How do I override C# properties and methods in IronPython?

Question

I have an interface with a base class in C# -- I'd like to be able to implement derived classes in IronPython for embedded extensibility.

In C# I would have something like:

public interface IInterface
{
    bool SomeProperty { get; set; }
    bool SomeMethod(DateTime atTime);
}

public abstract class BaseClass : IInterface
{
    public BaseClass() {}

    private bool someProperty = true;
    public virtual bool SomeProperty
    {
        get { return someProperty; }
        set { someProperty = value; }
    }

    public virtual bool SomeMethod(DateTime atTime)
    {
        return true;
    }
}

Then a controller type class

public class SomeOtherClass
{
    List<IInterface> interfaceCollection = new List<IInterface>();

    ... factory here to create C# classes and IPy classes derived from BaseClass or IInterface ...

    interfaceCollection.Add(somePytonDerivedClass);
    foreach (var intExersize in interfaceCollection)
    {
        if (intExersize.SomeProperty == true)
        {
            intExersize.SomeMethod(DateTime.Now);
        }
    }
}

I'd like to do an impl in IronPython -- something like:

class BaseClassIPy (BaseClass):
def __new__(self):
    print("Made it into the class")
    return BaseClass.__new__(self)

def __init__(self):
    pass

def get_SomeProperty(self):
    return BaseClass.SomeProperty

def set_SomeProperty(self, value):
    BaseClass.SomeProperty = value

def SomeMethod(self, atTime):
    return BaseClass.SomeMethod(atTime)

The new and init methods being called correctly --

but when I call the properties and methods on the IPy class, the calls seem to go directly to the base classes...

Is it a syntax issue? i.e. the IPy code is wrong?

Or am I missing something altogether?

Regards, Chad

---------------- Edit ----- method to inst python class:

private IInterface GetScriptPlugInNode()
{

    IInterface node = null;

    string plugInScript = "c:\\BaseClassIPy.py";
    string plugInClass = "BaseClassIPy";

    var options = new Dictionary<string, object>();
    ScriptRuntimeSetup setup = Python.CreateRuntimeSetup(options);
    setup.HostType = typeof(SelfContainedScriptHost);  //PAL impl
    setup.DebugMode = true;

    var pyRuntime = new ScriptRuntime(setup);
    var engineInstance = Python.GetEngine(pyRuntime);

    // Redirect search path to use embedded resources
    engineInstance.SetSearchPaths(new[] { String.Empty });

    var scope = engineInstance.CreateScope();

    ScriptSource source = engineInstance.CreateScriptSourceFromFile(plugInScript);

    source.Execute(scope);
    var typeClass = scope.GetVariable(plugInClass);
    var instance = engineInstance.Operations.CreateInstance(typeClass);
    node = instance;

    return node;

}

It looks like you're explicitly asking for the base method to be called - does your actual code do something else? — Jeff Hardy
– Jeff Hardy, Commented May 22, 2012 at 15:27
Yes, actual code does "work" -- I just setup the tests so I could set breakpoints in the code... none of the breakpoints in the overrides get "hit" — Chad Brockman
– Chad Brockman, Commented May 22, 2012 at 17:51
Try print statements; it may be an issue with the debugger. I'm confused because it should work. — Jeff Hardy
– Jeff Hardy, Commented May 22, 2012 at 18:48

Simon Opelt · Accepted Answer · 2012-05-22 06:28:18Z

1

You have to change the interface property/method in your abstract base class to be virtual in order to allow the IronPython class to properly inherit from that.

public abstract class BaseClass : IInterface
{
    public BaseClass() {}

    private bool someProperty = true;
    public virtual bool SomeProperty
    {
        get { return someProperty; }
        set { someProperty = value; }
    }

    public virtual bool SomeMethod(DateTime atTime)
    {
        return true;
    }
}

answered May 22, 2012 at 6:28

Simon Opelt

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5 Comments

Chad Brockman Over a year ago

Good point -- fixed my made up code... unfortunately it doesn't fix the problem.

Simon Opelt Over a year ago

I ran your code and as soon as I declared the methods in the base class the runtime bound to the python implementation... How are you creating your objects/instances? How are you verifying what happens?

Chad Brockman Over a year ago

Added code for creating class in original question... I'm verifying what happens by breakpoints getting hit in Visual Studio -- main and init get hit, the others do not. -- thanks!

Simon Opelt Over a year ago

Could you add print statements to def get_SomeProperty(self), def set_SomeProperty(self, value) and def SomeMethod(self, atTime) as Jeff suggested? This is what I did and as soon as I marked the base implementation virtual the python implementation got called.

Chad Brockman Over a year ago

Apologies! I was testing overrides on properties that were not set to virtual... A 2 week vacation cleared the head and allowed me to actually read your comment and check my code. Thanks!

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