windll exception

[Gordon McMillan]

Mike Palmer wrote:
> Below is a simple test file I wrote. It opens bwcc32.dll, and
> runs the BWCCGetVersion() function to get the version, then
> prints the version as a hex value. All that works fine.
> 
> As the output shows, an exception occurs when the program
> finishes, but ONLY if I run it from the command line (NT4, SP4).
> If open PythonWin and run it using execfile(), no exception is
> reported.
> 
> I thought the problem might be related to the bwcc.unload() line,
> but it doesn't matter whether I include that line or not. The
> error message is the same.
> 
> This leads me to believe that Python is generating the error on
> cleanup, and that somehow Python thinks None has been attached to
> a class in the same way that bwcc was when I called
> windll.module(). I suspect that I don't see the error from within
> PythonWin because it's only generated when PythonWin closes, and
> there probably isn't any mechanism to trap exceptions and report
> them on closing.
> 
> Can anyone confirm this? Is there any known fix or workaround?

You got most of it.

The solution goes something like this:

def __del__(self)
  xxx.free_library()

becomes:

def __del__(self, xxx=xxx):
  xxx.free_library()

The __del__ method (or whatever cleanup function) needs to 
squirrel away a reference to the module it is using. Otherwise, 
Python's order-of-destruction will clean up the module and set 
it to None, yielding the AttributeError.
 
> Thanks,
> 
> -- Mike --
> 
> ------- Python windll test file -------
> # Python windll test
> import windll
> bwcc = windll.module('bwcc32')
> ver  = bwcc.BWCCGetVersion()
> verstr = "%x" % ver
> print verstr # should print '10200'
> bwcc.unload()
> ----------------------------------------
> 
> ------- Output -------
> 10200
> Exception exceptions.AttributeError: "'None' object has no
>   attribute 'free_library'" in <method module.__del__ of module
>   instance at 7fd610> ignored
> ----------------------
> 
> 
> 
> 
> -- 
> http://www.python.org/mailman/listinfo/python-list



- Gordon