Python.NET - convert Python List to .NET List (C#)

Question

I am importing a python list (of string) in C# using Python.NET and I can't find any example of conversion from Python.NET dynamic object to C# List (all examples out there seems to be in the opposite direction C# to Python).

I tried to cast the dynamic python.net object with (List<string>) and with Enumerable.ToList<string>() but both failed. The as operator returned null. The only thing that worked was to loop over it with foreach... but is this really the only way and the best solution ?

Here is the code:

using (Py.GIL())
{
   dynamic MyPythonClass = Py.Import("MyPythonClass")
   dynamic pyList = MyPythonClass.MyList;
   
   //List<string> mylist = (List<string>)pyList;               //failed
   //List<string> mylist = Enumerable.ToList<string>(pyList);  //failed
   //List<string> mylist = pyList as List<string>;             //returns null

   List<string> mylist = new List<string>();
   foreach(string item in pyList)
   {
         mylist.Add(item);                                     //Success !
   }
}

@Prasad Telkikar : just tried and it returned null (with no error), I'll update the post. — bricx
– bricx, Commented Aug 27, 2020 at 18:01
I'm not familiar with this interop or python, but this looks like MyPythonClass.List has a runtime type that isn't a List<string> or assignable to it. Stick the debugger on and see what the run time type of pyList really is — Dave
– Dave, Commented Aug 27, 2020 at 18:02
List has a ctor that takes an IEnumerable (which we know we have cos we can foreach it) so use that var myList = new List<string>((IEnumerable<string>)pyList) — Dave
– Dave, Commented Aug 27, 2020 at 18:06
mm actually looking at the source csharp.hotexamples.com/site/… it doesn't actually implement IEnumerable, it takes advantage of little c# oddity that foreach statements use duck typing - it doesn't care about an interface just the presence of GetEnumerator and that GetEnumerator has to return something with Current and MoveNext() - so your casting is likely to never work and what you are doing is probably best — Dave
– Dave, Commented Aug 27, 2020 at 18:25

bricx · Accepted Answer · 2020-08-27 22:36:09Z

9

Answer was (shamefully) very simple, thanks to @Dave:

string[] mylist = (string[])pyList;

//or

List<string> mylist = ((string[])pyList).ToList<string>();

answered Aug 27, 2020 at 22:36

bricx

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1 Comment

roland kapl Apr 24 at 12:53

I would mention that the second form only works when you add using System.Linq; before. A method that works without Linq is using the List<string> constructor taking an array as an argument: List<string> mylist = new List<string>((string[])pyList);

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