Looking for advice: supporting multiple embedded interpreters

Paul Miller paul at fxtech.com
Thu Jan 22 15:46:04 CET 2004

Some background first - we have some software that embeds a Python 
interpreter into a host application. Scripts are loaded dynamically and 
used. But we want to support the ability to edit scripts while the app is 
running. This means we have to "unload" the script and cause a reload. 
Normal module reloading tricks don't work because if you try to reimport a 
script that imports another script, and if the nested script is changed, it 
might not be reloaded itself. Also, we have 2 parts of the software, each 
using Python for its own set of scripts. We don't want scripts loaded into 
each parts to "see" scripts loaded into the other part. Ideally, we would 
like multiple "instances" of a Python interpreter to manage this.

So, for Python 2.2, I came up with a system that works. When we need a new 
self-contained Python interpreter, I use Py_NewInterpreter(), swap it in 
using PyThreadState_Swap, load my built in modules, and swap it back out. 
When I need to run some code in that interpreter, I swap it back in, load 
the module I need, call methods in it, and swap it back out. When I'm done 
with the interpreter, I swap it back in and call Py_EndInterpreter.

When I want to force a reload of all the script code in a given 
interpreter, I just delete the interpreter, create a new one, and load the 
scripts into that one. This has worked flawlessly. And each "part" of my 
application can use a different interpreter without modules and globals in 
each one interfering with the other.

Now, with Python 2.3, this code doesn't seem to work anymore. Someone told 
me it is likely because of the extensive rewrite of GUSI or whatnot. It is 
important to note that I'm NOT really doing any threading. I just was 
self-contained interpreters for the above reasons.

What I am wondering is if there a reliable method in 2.3 that does what I 

It has recently come to my attention that Lutz Paelike is in exactly the 
same situation I am in, so I don't think this is a fringe concept.

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