handling return codes from CTYPES

MRAB python at mrabarnett.plus.com
Mon Jan 21 21:21:22 CET 2013

On 2013-01-21 16:52, Steve Simmons wrote:
> Mike,
> Thanks for your response - I was puzzled by one part of it though...
>      On 21/01/2013 15:14, Mike C. Fletcher wrote:
>>     That's because you've just discarded the object you created
> I (mis?)understood from the ctypes documentation that '>>> initResult =
> c_short(0)' would result in the creation of a ctypes 'short' called
> initResult and that this object would be mutable.  On that basis, I
> expected the following statement '>>> initResult = initScanLib( ... )'
> would assign the result of the call to initResult.
> So, I can understand that I am not using the correct approach but I
> don't understand how I discarded the object I created.  Can you clarify
> please?

initResult = initScanLib( ... )

will make initResult refer to whatever initScanLib(...) returned, just
as this:

initResult = c_short(0)

will make initResult refer to whatever c_short(0) returned.

What you were doing was this:

1. You created a c_short object and bound initResult to it.

2. You called a function and bound initResult to its result, unbinding
the c_short object in the process.

3. There were no other references to the c_short object, therefore it 
could be discarded by the garbage collector.

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