Re: handling return codes from CTYPES

Discussion in 'Python' started by MRAB, Jan 21, 2013.

  1. MRAB

    MRAB Guest

    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?
    >

    This:

    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.
    MRAB, Jan 21, 2013
    #1
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