[C++-sig] Handling exception thrown by Boost.Python c-extension in Python code

[English, Mark]

X-Replace-Address: mark.ignorethisbit.english at xxxrbccmxxx.ignorethisbittoo_and_removethosepreceding_xxxs_.com
This is a cross-posting of a reply-less message I posted in comp.lang.python a week ago, so apologies if I'm breaking rules. I suspect that was the wrong place.

I'm just getting started on Boost Python and may have missed this 
obvious looking problem somewhere. 

Given a c-extension "testext" written using Boost Python containing a 
base class "Base", a derived class "Derived", and a function 
"doSomething" which expects a "Derived" parameter, if I pass it a 
"Base" parameter an exception is thrown. This is a 
Boost.Python.ArgumentError. My question is how do I catch this error ? 


I tried the following bit of investigation: 
#Start code 
import testext 
b = testext.Base() 
try: 
   testext.doSomething(b) 
except Exception, e: 
    pass 
help(e.__class__) 
#End code 


which produces 
#Start output 
Help on class ArgumentError: 

class ArgumentError(exceptions.TypeError) 
 |  Method resolution order: 
 |      ArgumentError 
 |      exceptions.TypeError 
 |      exceptions.StandardError 
 |      exceptions.Exception 
 | 
 |  Methods inherited from exceptions.Exception: 
 | 
 |  __getitem__(...) 
 | 
 |  __init__(...) 
 | 
 |  __str__(...) 
#End output 

"print e" produces "<Boost.Python.ArgumentError instance>" 

So I could handle this by writing an except clause for TypeError. 

Boost.Python doesn't exist as a module i.e. it's not in sys.modules, 
and I don't know how to import it - should there be a Boost.Python 
module somewhere on my PythonPath that I've forgotten to setup ? 
Is there a standard way of catching these errors by their actual 
type ? 
Is there an easy way to export the exception classes from my c- 
extension (testext) so that I can use that ? Thus "except 
testext.ArgumentError" would catch the "Boost.Python.ArgumentError".


Thanks for any help, 
Mark 
mark.ignorethisbit.english at xxxrbccmxxx.ignorethisbittoo_and_removethosepreceding_xxxs_.com
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