Convert python objects to CLR objects dynamically #484

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1. den-run-ai commented on Jun 9, 2017

   

   den-run-ai

   on Jun 9, 2017

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   @yagweb can you share full code example? I'm not sure I fully understand.
2. den-run-ai

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   on Jun 9, 2017
3. yagweb commented on Jun 9, 2017

   

   yagweb

   on Jun 9, 2017

   Last edited by yagweb

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   @denfromufa

   Suppose a Python function,

   def test_py():
       return [1, "string", False]
   

   In C#, I want to call the function and convert the result to a CLR List<object>

   var res = test_py() //call the python function some way
   //now, I want to convert res into List<object>
   var converter = NewConverter()  //create a instance of PyConverter
   var b = converter.Convert(res)    //b is a List of CLR objects
   

   The PyConverter looks like,

   public class PyConverter
       {
           public PyConverter()
           {
               this.Converters = new Dictionary<IntPtr, Func<PyObject, object>>();
           }
   
           private Dictionary<IntPtr, Func<PyObject, object>> Converters;
           
           public void Add(IntPtr type, Func<PyObject, object> func)
           {
               this.Converters.Add(type, func);
           }
   
           public object Convert(PyObject obj)
           {
               if(obj == null)
               {
                   return null;
               }
               PyObject type = obj.GetPythonType();
               Func<PyObject, object> func;
               var state = Converters.TryGetValue(type.Handle, out func);
               if(!state)
               {
                   throw new Exception($"Type {type.ToString()} not recognized");
               }
               return func(obj);
           }
       }
   

   Here is the code how I use the PyConverter,

   public PyConverter NewConverter()
   {
              var converter = new PyConverter();
               using (Py.GIL())
               {
                   //XIncref is needed, or keep the PyObject
                   Converter.Add(PythonEngine.Eval("int").Handle, (args) => { return args.As<int>(); });
                   Converter.Add(PythonEngine.Eval("str").Handle, (args) => { return args.As<string>(); });
                   Converter.Add(PythonEngine.Eval("float").Handle, (args) => { return args.As<double>(); });
                   Converter.Add(PythonEngine.Eval("bool").Handle, (args) => { return args.As<bool>(); });
                   //Converter for list, omit here
               }
              return converter;
   }
   
   

   I want to find a better alternative for 'PythonEngine.Eval("int").Handle'. For example use the types in pythonnet, such as 'Runtime.PyIntType', but they are all internel.

   and what about adding this PyConverter function in pythonnet?
4. den-run-ai

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   on Jun 14, 2017
5. den-run-ai commented on Jun 14, 2017

   

   den-run-ai

   on Jun 14, 2017

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   This looks a little complicated API. Why not use PyInt and its equivalents for other types?

   https://github.com/pythonnet/pythonnet/blob/master/src/runtime/pyint.cs
6. yagweb commented on Jul 25, 2017

   

   yagweb

   on Jul 25, 2017

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   @denfromufa The example below shows that the element we get from a List (or Dict, Class attributes etc.) is wrapped in a PyObject class. (Or am I wrong?) So, PyInt etc. work only when we know the data type of the python object in advance, then we can call it in our code.

   using (Py.GIL())
   {
       var scope = Py.CreateScope();
       scope.Exec(
            "a=[1, \"2\"]"
       );
       dynamic a = scope.Get("a");
       object cc = a[0];
       Console.WriteLine(cc.GetType()); //print PyObject
       Console.WriteLine(cc.GetType() == typeof(PyInt)); //print false
       Console.WriteLine(cc);            
       scope.Dispose();
   }
   

   The problem here is we don't know the data type until runtime, or we want to have a single general converter to convert all these python objects into .NET object dynamically, instead writing lots of static convert functions.

   In our .NET program, we can

   1. Define Converters, register Convert functions for any class, include tuple, list, dict, ordereddict etc.
      Converters is stateless, so it can be defined once and used anywhere.
   2. Call python functions
   3. Use the Converters to convert PyObject into .NET object in a single line.
7. yagweb commented on Feb 11, 2018

   

   yagweb

   on Feb 11, 2018

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   This topic was merged into #623
8. yagweb

   closed this as completedon Feb 11, 2018