PyObject to NDArray #411

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1. Nucs commented on Sep 7, 2026

   

   Nucs

   on Sep 7, 2026

   Last edited by Nucs

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   @aaronavi, sorry for the very late reply. With the new NumSharp.Interop.pythonnet package (0.70.0, #628) you can pull the array straight out of the dict.

   Set up the Python engine once at startup - either point pythonnet at an installed Python, or deploy one from NuGet with Python.Included (no system install needed):

   using NumSharp;
   using NumSharp.Interop.PythonNet;
   using Python.Runtime;
   
   // Option A - existing Python: the PYTHONNET_PYDLL env var, or the DLL directly
   Runtime.PythonDLL = "python312.dll";   // or Environment.GetEnvironmentVariable("PYTHONNET_PYDLL")
   PythonEngine.Initialize();
   
   // Option B - deploy an embedded Python from NuGet (dotnet add package Python.Included)
   await Python.Included.Installer.SetupPython();
   await Python.Included.Installer.PipInstallModule("numpy");
   PythonEngine.Initialize();

   Explicit:

   using (Py.GIL())
   {
       // pyDict is your PyObject (a Python dict) holding a numpy array
       PyObject arr = pyDict["weights"];   // the ndarray, still a PyObject
       NDArray nd = arr.AsNDArray();        // -> NumSharp NDArray
       Console.WriteLine(nd.shape[0]);      // 4
   }

   Implicit (register the codec once, then use pythonnet's own As<NDArray>()):

   NDArrayPythonInterop.RegisterCodec();   // once per process
   
   using (Py.GIL())
   {
       PyObject arr = pyDict["weights"];
       NDArray nd = arr.As<NDArray>();      // implicit decode via the codec
       Console.WriteLine(nd.shape[0]);      // 4
   }

   Requires NumSharp.Interop.pythonnet (dotnet add package NumSharp.Interop.pythonnet). Closing.
2. Nucs

   closed this as completedon Sep 7, 2026