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POHow can I get methods to work as callbacks with python ctypes?
 

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  1. POHow can I get methods to work as callbacks with python ctypes?
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    <p>I have an C api that i'm interfacing with the python ctypes package. Everything works well, except this little tidbit.</p> <p>To register functions as callbacks to some notifications, i call this function :</p> <pre><code>void RegisterNotifyCallback( int loginId, int extraFlags, void *(*callbackFunc)(Notification *)) </code></pre> <p>so in python my code looks like :</p> <pre><code>CALLBACK = ctypes.CFUNCTYPE(None, ctypes.POINTER(Notification)) func = CALLBACK(myPythonCallback) myLib.RegisterNofityCallback(45454, 0, func) </code></pre> <p>If the value of myPythonCallback is a FunctionType (i.e. not a method), it works fine and calls the callback function with the correct parameters. If it's a MethodType, it still calls the method but then blows up with a segfault once the method is finished.</p> <p><em>edit</em></p> <p>To clarify, when i say function type i mean that myPythonCallback is defined as a function,</p> <pre><code>def myPythonCallback(Notification): ...do something with the Notification object i get passed in </code></pre> <p>When i say it's a MethodType, i mean a class method :</p> <pre><code>class MyClass(object): def myPythonCallback(self, Notification): ...do something with Notification </code></pre> <p>It blows up on the second type.</p> <p>Is there an easy away around this ? Or can someone offer me an explanation as to why this is happening ?</p> <p>Many thanks, Al.</p> <p><em>edit</em></p> <p>Digging a bit further with GDB gives me this :</p> <pre><code>Program received signal SIGSEGV, Segmentation fault. [Switching to Thread 1544567712 (LWP 5389)] 0x555ae962 in instancemethod_dealloc (im=0x558ed644) at Objects/classobject.c:2360 2360 Objects/classobject.c: No such file or directory. in Objects/classobject.c (gdb) backtrace #0 0x555ae962 in instancemethod_dealloc (im=0x558ed644) at Objects/classobject.c:2360 #1 0x555f6a61 in tupledealloc (op=0x5592010c) at Objects/tupleobject.c:220 #2 0x555aeed1 in instancemethod_call (func=0x558db8ec, arg=0x5592010c, kw=0x0) at Objects/classobject.c:2579 #3 0x5559aedb in PyObject_Call (func=0x558db8ec, arg=0x5592c0ec, kw=0x0) at Objects/abstract.c:2529 #4 0x5563d5af in PyEval_CallObjectWithKeywords (func=0x558db8ec, arg=0x5592c0ec, kw=0x0) at Python/ceval.c:3881 #5 0x5559ae6a in PyObject_CallObject (o=0x0, a=0x0) at Objects/abstract.c:2517 </code></pre> <p>and the value passed into instancemethod_dealloc is :</p> <pre><code>(gdb) x 0x558ed644 0x558ed644: 0x00000000 </code></pre> <p>Do you reckon this is fixable ?</p>
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    1. USAlMcLean
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      1. POHow can I get methods to work as callbacks with python ctypes?
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    1. COAre you using cdecl or stdcall in the C API? I don't know what you mean by the distinction between function type and method type. Please could you explain more, possibly with code samples of the form that works and the form that doesn't. By the way, I have successfully created callbacks with ctypes so I'm sure it's possible.
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      1. POHow can I get methods to work as callbacks with python ctypes?
      1. USDavid Heffernan
    2. COPlease see the edit.
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      1. POHow can I get methods to work as callbacks with python ctypes?
      1. USAlMcLean
 

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