"Er, among our chief weapons are fear, surprise, ctypes, gc, and fanatical devotion to the Pope!"
On Thu, Jun 23, 2016 at 1:03 PM, Devin Jeanpierre <jeanpierr...@gmail.com> wrote: > On Thu, Jun 23, 2016 at 8:19 AM, Guido van Rossum <gu...@python.org> > wrote: >> >> It was a long time when I wrote this, but IIRC the breakage could express >> itself as a segfault or other C-level crash due to some internal state >> invariant of the type object being violated, not just an exception. The >> existence of ctypes notwithstanding, we take C-level crashes very seriously. >> > > Big digression: one can still obtain the dict if they really want to, even > without using ctypes. I suppose don't actually mutate it unless you want to > segfault. > > >>> import gc > >>> class A(object): pass > >>> type(A.__dict__) > <class 'mappingproxy'> > >>> type(gc.get_referents(A.__dict__)[0]) > <class 'dict'> > >>> gc.get_referents(A.__dict__)[0]['abc'] = 1 > >>> A.abc > 1 > >>> > > (One can also get it right from A, but A can have other references, so > maybe that's less reliable.) > > I think I wanted this at the time so I could better measure the sizes of > objects. sys.getsizeof(A.__dict__) is very different > from sys.getsizeof(gc.get_referents(A.__dict__)[0]), and also different > from sys.getsizeof(A). For example: > > >>> import gc > >>> class A(object): pass > >>> sys.getsizeof(A); sys.getsizeof(A.__dict__); > sys.getsizeof(gc.get_referents(A.__dict__)[0]) > 976 > 48 > 288 > >>> for i in range(10000): setattr(A, 'attr_%s' % i, i) > >>> sys.getsizeof(A); sys.getsizeof(A.__dict__); > sys.getsizeof(gc.get_referents(A.__dict__)[0]) > 976 > 48 > 393312 > > (Fortunately, if you want to walk the object graph to measure memory usage > per object type, you're probably going to be using gc.get_referents already > anyway, so this is just confirmation that you're getting what you want in > one corner case.) > > -- Devin > -- --Guido van Rossum (python.org/~guido)
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