[IronPython] Calling Python objects from C#?

[Dino Viehland]

I think the problem is that AllocateObject is equivalent to calling mytype.__new__ which is not quite what you want - you want the equivalent of doing mytype () or mytype.__call__()

I would change this to:

            // Get the Python Class from the module's global list
            object ptype = module.Globals["MyClass"];

            // Create an instance of the object
            object myclass = Ops.Call(ptype);

Not only is it more correct it gets rid of the direct dependency on UserType (for example your code wouldn't have worked w/ an old-style class or if a user had done MyClass = System.SomeTypeThatHasADoWorkMethod).

>From there I think your Ops.Invoke calls should work (although I haven't tried to make sure).


-----Original Message-----
From: users-bounces at lists.ironpython.com [mailto:users-bounces at lists.ironpython.com] On Behalf Of michael_sweeney at agilent.com
Sent: Monday, January 15, 2007 9:58 AM
To: users at lists.ironpython.com
Subject: [IronPython] Calling Python objects from C#?

Hi All,

My apology if this has been asked before... I have searched for several examples and did not find what I was looking for.

My question is what is the best way to interact with Python objects from within C#? I need to call functions, capture the return value and get/set attributes from within C#.

I have tried several ways and ended up with this example for calling functions, but it generates an exception saying it does not know what "attr" is.

Here is my example:

File MyExample.py:

class MyClass(object):
    def __init__(self):
        self.attr = 500.0

    def DoWork(self):
        print "Attr = ", self.attr
        return self.attr


File Program.cs:

using System;

using IronPython.Runtime;
using IronPython.Runtime.Types;
using IronPython.Runtime.Operations;
using IronPython.Hosting;
using IronPython.Modules;

namespace IPyExample
{
    class Program
    {
        static void Main(string[] args)
        {
            PythonEngine engine = new PythonEngine();
            EngineModule module = engine.CreateModule("MyExample", true);

            try
            {
                engine.ExecuteFile("MyExample.py", module);
            }
            catch (Exception ex)
            {
                Console.WriteLine("Failed to execute Example.py file");
                Console.WriteLine("Exception: {0}", ex.Message);
                return;
            }

            // Get the Python Class from the module's global list
            UserType ptype = module.Globals["MyClass"] as UserType;

            // Create an instance of the object
            object myclass = ptype.AllocateObject();

            // Call the method - Using Ops.Invoke()
            Ops.Invoke(myclass, SymbolTable.StringToId("DoWork"));

            // Call the same method - Using UserType.Invoke()
            object rtnValue = ptype.Invoke(myclass,
                SymbolTable.StringToId("DoWork"));

            Console.WriteLine("DoWork return value = {0}\n", rtnValue);
        }
    }
}


Exception:

C:\Documents and Settings\sweeneym\My Documents\Visual Studio 2005\Projects\ATF.
IP\IPyExample\bin\Debug>IPYExample
Attr =
Unhandled Exception: System.MissingMemberException: attr
   at IronPython.Runtime.Types.UserType.GetAttr(ICallerContext context, Object self, SymbolId name) in C:\Development\Ir
onPython-1.1\Src\IronPython\Runtime\Types\UserType.cs:line 370
   at IronPython.Runtime.Operations.Ops.GetAttr(ICallerContext context, Object o, SymbolId name) in C:\Development\IronP
ython-1.1\Src\IronPython\Runtime\Operations\Ops.cs:line 1644
   at DoWork$f1##4(FunctionEnvironment4Dictionary , Object )
   at IronPython.Runtime.Calls.CallTarget1.Invoke(Object arg0)
   at IronPython.Runtime.Calls.Function1.Call(ICallerContext context, Object arg0) in C:\Development\IronPython-1.1\Src\
IronPython\Runtime\Calls\Function.Generated.cs:line 127
   at IronPython.Runtime.Calls.Function1.Call(ICallerContext context, Object[] args) in C:\Development\IronPython-1.1\Sr
c\IronPython\Runtime\Calls\Function.Generated.cs:line 138
   at IronPython.Runtime.Calls.PythonFunction.CallInstance(ICallerContext context, Object instance, Object[] args) in C:
\Development\IronPython-1.1\Src\IronPython\Runtime\Calls\Function.cs:line 389
   at IronPython.Runtime.Calls.Method.Call(ICallerContext context, Object[] args) in C:\Development\IronPython-1.1\Src\I
ronPython\Runtime\Calls\Function.cs:line 972
   at IronPython.Runtime.Operations.Ops.Call(Object func, Object[] args) in C:\Development\IronPython-1.1\Src\IronPython
\Runtime\Operations\Ops.cs:line 1414
   at IronPython.Runtime.Types.DynamicType.Invoke(Object target, SymbolId name, Object[] args) in C:\Development\IronPyt
hon-1.1\Src\IronPython\Runtime\Types\DynamicType.cs:line 1010
   at IronPython.Runtime.Operations.Ops.Invoke(Object target, SymbolId name, Object[] args) in C:\Development\IronPython
-1.1\Src\IronPython\Runtime\Operations\Ops.cs:line 1760
   at IPyExample.Program.Main(String[] args) in C:\Documents and Settings\sweeneym\My Documents\Visual Studio 2005\Proje
cts\ATF.IP\IPyExample\Program.cs:line 35


------------------------------------------------------------
Michael A. Sweeney        email: michael_sweeney at agilent.com
Agilent Technologies      phone: (509) 921-4395
MS:3WU-222                fax:   (509) 921-3991
24001 E. Mission Ave.
Liberty Lake, WA 99019 USA
------------------------------------------------------------

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