On 28 August 2016 at 08:25, Terry Reedy <tjre...@udel.edu> wrote: > Slicing can be made to malfunction and even crash with an 'evil' __index__ > method. https://bugs.python.org/issue27867 > > The crux of the problem is this: PySlice_GetIndicesEx > receives a slice object and a sequence length. Calling __index__ on the > start, stop, and step components can mutate the sequence and invalidate the > length. Adjusting the int values of start and stop according to an invalid > length (in particular, one that is too long) will result in invalid results > or a crash. > > Possible actions -- very briefly. For more see end of > https://bugs.python.org/issue27867?@ok_message=msg 273801 > 0. Do nothing. > 1. Detect length change and raise.
I suggest taking this path - it's the lowest impact, and akin to the "dictionary changed size during iteration" runtime error. __index__ having side effects is pathological code behaviour, so we really just need to prevent the interpreter crash, rather than trying to make it sense of it. Cheers, Nick. -- Nick Coghlan | ncogh...@gmail.com | Brisbane, Australia _______________________________________________ Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
