wxPython gurus, please help

[Jive Dadson]

    I have an application that opens an image file of the user's choice. 
   I have an exception handler for the case that the user selected a bad 
or unsupported image file.  My code is catching the exception, but 
unfortunately for me, after I exit the except-clause, wxPython is 
popping up its own message dialog from somewhere in deepest, darkest 
__core__.

    How do I make it not do that?

    Thankee much,
    Jive