On 2017-08-04 10:49, Vincent Delecroix wrote:
Indeed, this is a subtle issue

Cython thinks that F is a sequence because Family does support the
sequence protocol (this is lost somewhere in the macro
__Pyx_GetItemInt). As a consequence, Cython translates a negative index
"-i" into "len(sequence) - i". Which is indeed wrong in the above
case... Cython should have called PyObject_GetItem.

I can try to write a Cython bug report if nobody has done that already.

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