​@Matt H 

TL;DR led_source.SourcesData.SamplingMethod = ZOSAPI.Editors.NCE.SourceSamplingMethod.Sobol

I haven’t tested, but this is a recurring issue we’ve seen in the Community.

In the Programming..ZOS-API Help..ZOS-API Syntax Help, you find the following description for SourceData. 

I imagine you have found it before. But I wanted to highlight something. If you look to the left of PrePropagation and SamplingMethod. There’s some text that I marked with a yellow marker. It reads double and SourceSamplingMethod, respectively. This tells you the type of variable that is expected from the corresponding property. Double is a standard floating-point numeric variable. Therefore, when you do:

led_source.SourcesData.PrePropagation = -1

Everything works. In effect, -1 is an integer (int), but it is automatically cast to a double (-1.0). No problem with that. But when you do:

led_source.SourcesData.SamplingMethod = "Sobol"

There’s a problem because “Sobol” is interpreted as a string because of the quotation marks. Therefore, SamplingMethod tries to cast the string to the required type SourceSamplingMethod, but it can’t.

So, how do you set the source sampling method then? You see an example a bit below in the same help page with ArrayType. I’m copying the Python implementation only since it seems to be what you are using.

Look at what is being set to ArrayType:ZOSAPI.Editors.NCE.ArrayMode.Rectangular. To do the same with the source sampling method, you can click on the SourceSamplingMethod that I highlighted in my first screenshot, and it’ll take you to this page.

Right under the section header, you see a sequence that looks like what’s been set for the ArrayType example. And this is exactly what you need to use:

led_source.SourcesData.SamplingMethod = ZOSAPI.Editors.NCE.SourceSamplingMethod.Sobol

I hope this helps and take care,

David