[IronPython] How to force ipy-engine to reload imported modules ?

Michael Foord fuzzyman at voidspace.org.uk
Mon Feb 5 17:53:22 CET 2007

Langer, Jochen ALRT/EEG2 * wrote:
> We use IronPython-engine embedded in a C# application. The engine 
> executes Python-scripts that are located in several directories with 
> ExecuteFile(). The scripts import modules that are located in 
> subfolders of folder of the respective script.
> Doing so the following problem occurs:
> 1. Executing ScriptA in DirectoryA imports Modules that are located in 
> subdrectories of DirectoryA - still everything is fine
> 2. Executing ScriptB in DirectoryB does not import modules if a module 
> with the same name had been imported during the previous call to 
> ExecuteFile("DirectoryA\ScriptA"). The previously imported modules 
> (belonging to ScriptA) are used instead.
> As a workaround we create a new engine prior to each execution and 
> dispose it afterwards. 
> But this is not the preferred implementation - I'd rather like to have 
> one static engine-object that can be used multiple times. (putting all 
> scripts into the same folder or using different module-names is not an 
> option due to maintainance and reuse)
> Any suggestions how the ipy-engine can be forced to reload modules 
> upon each call to ExecuteFile() ?
Reusing previously imported modules (recognised by name) is a feature 
not a bug. :-)

I'm not sure what the best approach from 'outside' the engine is, but 
there are a couple of Python tricks to get this to work as you expect.

Imported modules are stored in 'sys.modules' (a dictionary - keyed by 
the module name).  Deleting entires from here will cause them to be 
reloaded next time you import.

If you make your top level directory a package you can import using 
absolute references. E.g. if you have your main application libraries in 
a directory called main and then two subdirectories called 'a' and 'b' 
and you want to import modules from both a and b.  Add empty 
'__init__.py' files to directories a and b and then import using :

from Main.a import module
from Main.b import module

The entries in sys.modules will then be 'Main.a.module' and 
'Main.b.module'; which don't clash.


I'm sure there are alternative approaches from the C# sharp.

All the best,

Michael Foord

> regards,
> Jochen
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