On Wednesday, June 13, 2012 05:32:26 PM Nathan Smith wrote: > We don't want to raise a RuntimeError when calling the hash function in > Shiboken because of the very reason you stated. Doing something that > raises exceptions in the hash function will break any container that uses > hashes (weak references, sets, dicts, weakref.WeakSet, probably many more). > Returning default error values has a similar effect. > > My most recent approach was to return the address of the shiboken object, > which is address of the PyObject. I tried this approach (I haven't > submitted it yet) on the example you provided below, and it seems to work. > I've been using it with my code for a few days now, and it's been working > well. > > Note that using the address method has the drawback that two objects > separated in time may have the same hash value because they may land at the > > same memory address. You can see this in the following test case: > >>> hash(QtCore.QObject()) == hash(QtCore.QObject()) > > True > > > The first QObject is created, the hash is taken of it, and then it is > destroyed. The reference count drops to 0, so the Shiboken handle is > cleaned up. A second QObject is created (at the same address as the first > QObject), the hash is taken of it, and then it is destroyed. This could be > avoided if we kept a running counter of SbkObject instances and used the > counter as the hash value (which I think is overkill). > > Incidentally, what is the difference between shiboken.delete and > shiboken.invalidate? There don't appear to be any docstrings in the > shiboken module and invalidate isn't in the online documentation.
The docs are on the PSEP[1] and on Shiboken docs[2]. delete really deletes the underlying C++ object then invalidate the Python object, i.e. any use of this object will raise a exception. invalidate only invalidates the Python object, causing it to raise an exception when used. [1] http://www.pyside.org/docs/pseps/psep-0106.html [2] http://www.pyside.org/docs/shiboken/shibokenmodule.html > Nathan > > On Wed, Jun 13, 2012 at 3:45 PM, John Ehresman <[email protected]> wrote: > > On 5/30/12 3:35 PM, John Ehresman wrote: > >> Can we use the address of the Shiboken object as the hash value? That > >> > >>> remains valid so long as there are references to the object, even after > >>> the object itself has been deleted in C++ land. > >> > >> This works if there can only be one wrapper at a time for a given > >> QObject. I don't know if this is the case. > > > > I just ran into this bug and tried to apply the patch locally, but ran > > into poblems. If the address of the PyObject* can be used, I think that > > > > would be preferable. Consider the following: > > o = QObject() > > d = {} > > d[o] = 1 > > > > def on_destroy(): > > d.pop(o) > > > > o.destroyed.connect(on_**destroy) > > shiboken.delete(o) > > > > The pop in the destroy handler will fail with a RuntimeError and even if > > the RuntimeError is suppressed and a default hash value returned, the > > entry > > in the dictionary won't be found or removed. > > > > John
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