[IronPython] IronPython 2: Oddity with Hosting API from within IronPython

[Michael Foord]

Curt Hagenlocher wrote:
> I don't know the answer to your question (and don't have the source 
> code with me on the bus) but by calling Python.CreateEngine(), you're 
> now creating a second copy of the runtime.  Notionally, the runtimes 
> are independent of each other and I would expect there to be a second 
> import when the same module is used in both.

Yes - which is why the code explicitly adds the module to the runtime 
associated with the engine we have just created. At least the theory was 
that this would publish the already imported module to the new engine, 
and make it available for import without having to re-execute the module.

Michael

>
> On Fri, Oct 31, 2008 at 6:53 AM, Michael Foord 
> <michael.foord at resolversystems.com 
> <mailto:michael.foord at resolversystems.com>> wrote:
>
>     Hello guys,
>
>     In Resolver One we use the IronPython hosting API from inside
>     IronPython code. I've noticed an oddity that is not how I would
>     expect the hosting API to behave if I was using it from C#.
>
>     My understanding is that the correct way to publish a module (make
>     it available for a ScriptEngine to import) is to set it in
>     'engine.Runtime.Globals'.
>
>     If I do this from within IronPython code with a module I have
>     already imported and then execute an import statement in the
>     engine, the module is re-imported (code executed) rather than
>     using the one I have published to the runtime globals.
>
>     If I have a 'foobar' module that prints when importing, the
>     following code prints twice instead of the once I would expect:
>
>     import sys
>     import clr
>     clr.AddReference('IronPython')
>     clr.AddReference('Microsoft.Scripting')
>
>     from IronPython.Hosting import Python
>     from Microsoft.Scripting import SourceCodeKind
>
>     import foobar
>
>     engine = Python.CreateEngine()
>     engine.Runtime.Globals.SetVariable('foobar', sys.modules['foobar'])
>
>     source = engine.CreateScriptSourceFromString('import foobar\r\n',
>     SourceCodeKind.Statements)
>     scope = engine.CreateScope()
>     source.Compile().Execute(scope)
>
>
>     *However*, if I change the code to not use Runtime.Globals, but
>     instead do the following, then the module is only imported once
>     and I get one print as expected:
>
>     hostedSys = Python.GetSysModule(engine)
>     hostedSys.modules['foobar'] = sys.modules['foobar']
>
>     Is there something I have overlooked here?
>
>     As a minor supplementary question, how do I get a reference to the
>     default ScriptScope on an engine? Is there any performance
>     advantage in using the default one, can I replace it, and does
>     replacing it remove any performance benefits we might have got?
>     (OK, so strictly speaking that wasn't just one question...)
>
>     All the best,
>
>     Michael Foord
>
>     -- 
>     Michael Foord
>     Senior Software Engineer, Resolver Systems Ltd.
>     michael.foord at resolversystems.com
>     <mailto:michael.foord at resolversystems.com>
>     +44 (0) 20 7253 6372
>
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>
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