Hello, I was learning Cython from this tutorial when I noticed a glitch: Near the end, after boundscheck False, some variables are changed to unsigned int. But this has unexpected consequences: variables t_from and such are not determined correctly, as one of the arguments is negative, but gets cast to unsigned for comaprison. (Yes, this is a weird feature of C.) Actually, the use of unsigned does not seem to have any impact on performance, so I suggest to scratch that part of tutorial. Just explain that with boundscheck off, negaitive indices no longer work. (But there might perhaps be one small improvent in cython itself: with boundscheck off, the index might be cast to unsigned before it is used: this way we probably crash on negative values, instead of silently accessing the negative offset of the array data.) Thank you for nice piece of software, Stepan Kasal