[IronPython] Limitations of PythonEngine.CreateMethod<TDelegate>?

[Alex Henderson]

Thanks Dino, I'll keep an eye on the issue and see how you get on :)

> -----Original Message-----
> From: users-bounces at lists.ironpython.com [mailto:users-
> bounces at lists.ironpython.com] On Behalf Of Dino Viehland
> Sent: Tuesday, 10 October 2006 1:10 p.m.
> To: Discussion of IronPython
> Subject: Re: [IronPython] Limitations of
> PythonEngine.CreateMethod<TDelegate>?
> 
> Thanks for the report - this sounds like a bug.  I suspect we're not
> creating the function w/ the proper environment in this case, but I
> haven't had a chance to investigate.  I've opened CodePlex bug #4196 for
> this.
> 
> -----Original Message-----
> From: users-bounces at lists.ironpython.com [mailto:users-
> bounces at lists.ironpython.com] On Behalf Of Alex Henderson
> Sent: Friday, October 06, 2006 8:51 PM
> To: users at lists.ironpython.com
> Subject: [IronPython] Limitations of PythonEngine.CreateMethod<TDelegate>?
> 
> Hi All,
> 
> I've been playing with the PythonEngine's CreateMethod<TDelegate>(..) and
> declaring functions within the body of another function - however it
> doesn't seem to work, for example I can writin a function like this:
> 
> def ExternalFunc():
>         def InnerFunc1():
>                 def InnerFunc2():
>                         return "2"
>                 return "1" + InnerFunc2()
>         return "0" + InnerFunc1()
> 
> and then evaluate it...
> 
> >>> ExternalFunc()
> '012'
> >>>
> 
> But when I try to create a delegate for doing the same thing by shedding
> the outer "layer" of the function, and creating it as a method via the
> PythonEngine it doesn't work:
> 
> PythonEngine = new PythonEngine()
> // some more setup code would go here...
> Func<string> externalFunc = engine.CreateMethod<Func<string>>(@"def
> InnerFunc1():
>     def InnerFunc2():
>         return ""2""
>     return ""1"" + InnerFunc2()
> return ""0"" + InnerFunc1()");
> 
> The call to CreateMethod spits the dummy, with a NullReferenceException...
> here's the stack trace
> 
> failed: System.NullReferenceException : Object reference not set to an
> instance of an object.
>         at
> IronPython.Compiler.Generation.CodeGen.DefineDynamicMethod(String
> name, Type retType, Type[] paramTypes)
>         at IronPython.Compiler.Generation.CodeGen.DefineMethod(String
> name, Type retType, Type[] paramTypes, SymbolId[] paramNames)
>         at IronPython.Compiler.Ast.FunctionDefinition.Emit(CodeGen cg)
>         at IronPython.Compiler.Ast.SuiteStatement.Emit(CodeGen cg)
>         at
> IronPython.Compiler.Ast.FunctionDefinition.EmitFunctionBody(CodeGen cg,
> CodeGen ocg)
>         at
> IronPython.Compiler.Ast.FunctionDefinition.EmitFunctionImplementation(Code
> Ge
> n methodCodeGen, CodeGen initCodeGen)
>         at
> IronPython.Hosting.PythonEngine.CreateDelegateWorker[TDelegate](Statement
> s,
> IList`1 parameters)
>         at
> IronPython.Hosting.PythonEngine.CreateMethodUnscoped[TDelegate](String
> statements, IList`1 parameters)
>         at IronPython.Hosting.PythonEngine.CreateMethod[TDelegate](String
> statements, IList`1 parameters, EngineModule engineModule)
>         at IronPython.Hosting.PythonEngine.CreateMethod[TDelegate](String
> statements)
> 
> Am I overlooking something in my code, or is this just a limitation of
> using CreateMethod<TDelegate> to get a delegate to an anonymous python
> function?
> 
> For the mean time I'm just working around it by doing this:
> 
> engine.Execute(@"def ExternalFunc():
>     def InnerFunc1():
>         def InnerFunc2():
>             return ""2""
>         return ""1"" + InnerFunc2()
>     return ""0"" + InnerFunc1()");
> 
> PythonFunction func = _engine.EvaluateAs<PythonFunction>("ExternalFunc");
> 
> Func<string> funcDel = delegate { return (string)func.Call(); };
> 
> Which gets me a suitable delegate, but it's not really the same as I end
> up having to declare the function as part of a module, which I was trying
> to avoid...
> 
> Chez,
> 
>  - Alex
> 
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