The open source UML tools can be really tricky. Even though exporting/importing in XMI, there seem to be a lot of incompatibilities between tools.
Thus, I wonder if anybody found a good workflow for generating python code from UML models created in ArgoUML, using Open Source tools?
Did you try http://argouml-python.tigris.org/ ? If that doesn't suit, perhaps you could file bug reports so that people could fix the problems.
If you're looking for a different tool, you'll want one which accepts UML 1.4 which is what most recent versions of ArgouML implement.
BTW, the UML/XMI compatibility problem isn't unique to open source UML tools. It's all rooted in the OMG's complete disregard for compatibility among versions of UML. Pretty much the only time they maintained compatibility was UML 1.5 which is a pure superset of UML 1.4. All other versions of UML are completely incompatible -- UML 2.x and UML 1.x hugely so.