Sebastian Haase wrote: > Hi, > Before I start I want to admit that I don't understand much about > this. I just saw that the memmap class defines __del__ and that I had > problems in the past when I added a 'def __del__' to a class of mine. > So here is a quote, I would like to know if this is "standard > knowledge" on this list or not. > > # I found the info originally here: http://arctrix.com/nas/python/gc/ > # Circular references which are garbage are detected when the > optional cycle detector is enabled (it's on by default), but can only > be cleaned up if there are no Python-level __del__() methods involved. > Refer to the documentation for the 'gc' module for more information > about how __del__() methods are handled by the cycle detector, > particularly the description of the garbage value. Notice: [warning] > Due to the precarious circumstances under which __del__() methods are > invoked, exceptions that occur during their execution are ignored, and > a warning is printed to sys.stderr instead. Also, when __del__() is > invoked in response to a module being deleted (e.g., when execution of > the program is done), other globals referenced by the __del__() method > may already have been deleted. For this reason, __del__() methods > should do the absolute minimum needed to maintain external invariants. > > This is particularly annoying when using ctypes, and you need to clean some ressources. I had this problem with pyaudiolab:
Class A def __init__(self): # here call C library open def close(self): # here dispose of all handlers related to the file def __del__(self): # here dipose of all handlers (if not cleaned by close) As mentionned in the above paragraph, the problem is that sometimes (typically, when exiting the python interpreter) the C library reference is "out of scope" (not sure the expressionis appropriate for python) before calling __del__ on an instance of A. I am using ctypes for the interface with C in this case, so what I do is: def __del__(self, close_func = _snd.sf_close): # Stupid python needs the close_func, otherwise # it may clean ctypes before calling here if not(self.hdl == 0): close_func(self.hdl) self.hdl = 0 This is not pretty, and you better not call __del__ with your own close_func function, but that's the only solution I can think of. David _______________________________________________ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
