[IronPython] Using CLR bound COM interfaces

[Alex Willmer]

Hello,

I've been attempting with IronPython, to access the CLR binding to
ArcObjects[1], a COM based Geographic Information System (GIS) library.
I come at this from a CPython background, so my knowledge of COM & .NET
are lacking.

I'm trying to understand how interfaces (IFoobar) are dealt with in
IronPython. A C# example I'm attempting to transcribe contains the
following lines:

if (!((objectWorkspace is IWorkspace) || 
     (objectWorkspace is IFeatureDataset)))
  {
    throw(new Exception(....));
  }

My assumption was that isinstance() would replace 'is', but the
following would indicate otherwise. From the .NET 2.0 docs[2] the
System.Uri class inherits from ISerializable

>>> import System 
>>> import System.Runtime.Serialization 
>>> x = System.Uri('http://example.net') 
>>> isinstance(x, System.Uri)
True
>>> isinstance(x, System.Runtime.Serialization.ISerializable)
False

How should I test a particular object implements an interface?

My second query is based on the following C#:

    IGeometryDefEdit geometryDefEdit = (IGeometryDefEdit) geometryDef;

    // Assign Geometry Definition
    geometryDefEdit.GeometryType_2 = geometryType;
    geometryDefEdit.GridCount_2  = 1;
    geometryDefEdit.set_GridSize(0, 0.5);
    geometryDefEdit.AvgNumPoints_2 = 2;
    geometryDefEdit.HasM_2 = false;
    geometryDefEdit.HasZ_2 = true;

I understand that to transcribe this is I should forget the
assignment/cast and replace geometryDefEdit.Method(args) with
IGeometryDefEdit.MethodName(geometryDef, args). Is this correct?

Many thanks.

Alex Willmer

[1] http://edndoc.esri.com/arcobjects/9.1/
[2] http://msdn2.microsoft.com/en-us/library/system.uri.aspx