Cannot get correct overload of generic method

[Tobimaru]

Environment

• Pythonnet version: zip archive of master branch
• Python version: 3.6
• Operating System: Ubuntu 18.04

Details

• Describe what you were trying to get done.

Invoke a generic method with multiple overloads.

• What commands did you run to trigger this issue?

On the C# side I have the following generic method with overloads:

Variable<T> Variable.Constant<T>(T)
VariableArray<T> Variable.Constant<T>(T[])    

On the python side, I'm trying to invoke the second overload by doing:

a = Variable.Constant(System.Array[System.Double]([1.0, 2.0, 3.0]))

But when I check the type of a, it gives Variable[System.Double[]] and not VariableArray[System.Double]. This makes sense since it's ambiguous without specifying the type of the output variable or specifying the type for the function. Since in python I can't pin the output variable to a specific type, I tried to resolve the ambiguity with:

a = Variable.Constant[System.Double](System.Array[System.Double]([1.0, 2.0, 3.0]))

but then I get the exception:

TypeError: No method matches given arguments for Constant

I also tried:

a = Variable.Constant.Overloads[System.Double](System.Array[System.Double]([1.0, 2.0, 3.0]))

but then I get the exception:

TypeError: No match found for signature

It seems that there is pull-request (#227) ongoing, but it looks to have been work in progress for quite a while now. Is this is not priority, is there a workaround that I can try?

[filmor]

The method overload resolution of Python.NET is very tricky to get right, as we're dealing with two different type systems that should somehow be made compatible. I'm not sure how #227 would solve this.

[Tobimaru]

Is there any way to work around this problem? The only thing I can think of is to write a small C# library that explicitly instantiates the generic methods with the types that I need. I hope that python.NET can then resolve the overloads.

[filmor]

Yes, that approach works fine, and I'm currently not aware of a workaround that doesn't require an additional library.

[den-run-ai]

You can always use reflection, search this issue tracker or stackoverflow "python.net" tag.

[Tobimaru]

Sorry for the late response. Thanks for the info. I tried with a wrapper library around the generic methods and that seems to work. But now I'm having issues with [] overloads. I haven't tried with using reflections yet, I'll give it a try.

[Tobimaru]

Reflection doesn't seem to work either. The problem is that in the module that I'm trying to use (infer.net), Variable is an abstract class and Constant is a static method of this abstract class. I don't know how to invoke the method of an abstract class. If I do:

var_type = dll.GetType("Variable")
method = var_type.GetMethod("Constant")

Then I get the error:

AttributeError: 'NoneType' object has no attribute 'GetMethod'

[christabella]

This is probably too late but an infer.net-specific workaround could be to use Invoker.InvokeStatic(Variable, "Constant", args) e.g. https://github.com/dotnet/infer/blob/0c75b5ef4190c5eee55e663741e645cb997b7236/test/TestPython/test_tutorials.py#L217