Ref/Out on 2D Array with Ironpython

Question

I have a python script that needs to do some communication with a C# function. The function expects three parameters, two of which are returned via the out keyword. The declaration looks something like this:

RunComputation(InfoParams locInfo, out double[,] dataTable, out int numPoints){ ... }

Since Python is a dynamically typed language, it doesn't know how to deal with the out keywords. I did some searching and found some stuff about clr.StrongBox and clr.Reference, which seem fairly simple to use in situations where you need to pass a strongly typed object.

For the numPoints parameter, I can define something like this in the python code:

 num_points = clr.Reference[int]

And it seems to be fine. The problem comes from the dataTable array. I don't know the syntax to tell it that my strongly typed object is an array of doubles. The error it gives informs me that it's expecting an instance of Type StrongBox[Array[float]]. I tried import Array from System to see if I could add that C# type in as a reference, but it failed. Any ideas?

I don't know much about IronPython programming, but perhaps you can consider adding a C# wrapper function that takes your single InfoParams parameter and returns an object composing of both the double[,] dataTable and int numPoints. That way C# handles the outs and IronPython just gets an object from which it can access that data via its two exposed properties. — Chris Sinclair
– Chris Sinclair, Commented May 10, 2012 at 20:22
Makes sense. I'll give that a go while I wait to see if someone has a direct solution. — KChaloux
– KChaloux, Commented May 10, 2012 at 20:24

digEmAll · Accepted Answer · 2012-05-10 20:59:35Z

1

If you are using only out arguments you can also use the implicit way, i.e. if you don't pass any out argument to the method, they're returned as a tuple.

e.g.

d = Dictionary[str, float]()
(keyfound,value) = d.TryGetValue("b")

It works also with ref arguments.
Imagine to have the following method:

int Foo(int x, double[,] v)

you can call the method in this way:

nrows = 5
ncols = 5
array = Array.CreateInstance(float, nrows, ncols)
(x, arrayNew) = obj.Foo(3, array)

and finally, the modified value of array is contained into arrayNew

edited May 10, 2012 at 20:59

answered May 10, 2012 at 20:36

digEmAll

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