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

[Dino Viehland]

We try to import from the file system before we attempt to import from the DLR (which includes both globals & .NET namespaces).  So in this case we'll pick up foobar from disk because presumably these 2 engines both share the entry in sys.path where foobar lives.

I think long term this logic is going to move into an importer hook because by CPython 3.1 the import logic may be written entirely in Python.  In that case you'd have the ability to re-order the import hooks so you could control the precedence.  But for now I think it's by design - we don't want to block potentially valid imports that would work in CPython (e.g. import System :) ).

-----Original Message-----
From: users-bounces at lists.ironpython.com [mailto:users-bounces at lists.ironpython.com] On Behalf Of Michael Foord
Sent: Friday, October 31, 2008 6:54 AM
To: Discussion of IronPython
Subject: [IronPython] IronPython 2: Oddity with Hosting API from within IronPython

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
+44 (0) 20 7253 6372

Try out Resolver One! <http://www.resolversystems.com/get-it/>

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