C-API proper initialization and deallocation of subclasses

Discussion in 'Python' started by ptb, Jun 13, 2014.

  1. ptb

    ptb Guest

    Hello all,

    I decided to play around with the C-API and have gotten stuck. I went through the Shoddy example (https://docs.python.org/3/extending/newtypes.html#subclassing-other-types) in the docs and tried to extend it by adding a method which creates and returns a shoddy instance. I dug around to find ways to allocate and initialize my shoddy instance and that seems to work well. However, I get segfaults when I try to delete my instance. The code is inthe gist: https://gist.github.com/pbrady/f2daf50761e458bbe44a

    The magic happens in the make_a_shoddy function.

    Here's a sample session (Python 3.4.1)
    tup build
    shd allocated
    list style allocation successful
    Py_SIZE(list) : 5
    Py_SIZE(shoddy) : 5
    Segmentation fault (core dumped)

    This happens even if I don't set the destructor. Any ideas on what I am doing wrong?

    ptb, Jun 13, 2014
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  2. ptb

    ptb Guest

    While there doesn't appear to be too much interest in this question I thought I would post the solution. I had to modify shoddy by adding the proper flags and clear/traverse methods such to ensure that cyclic garbage collection was properly handled. I'm not quite sure why I had to do this since myshoddy instance did not have any cyclic references but I'm wondering if itwas necessary since it's a subclass of list which has all the cyclic GC machinery in place. I suspect I won't understand the answer but if someone with more knowledge can clear things up, that would great.

    ptb, Jun 13, 2014
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