Stefan Krah added the comment: But only Cython does not set suboffsets to NULL and you already have a small patch to fix that. The Python 3 docs say "suboffsets only if needed" and the PEP says the same, so the situation is not completely undocumented. I think your doc patch goes too far. Buffers propagate in unpredictable ways, and since the original consumer request is *not stored* in the buffer, setting unneeded fields to NULL provides a way to figure out the original request. It is actually *an optimization* to set suboffsets to NULL: Compliant code that uses arbitrary buffers always has to check for: if (suboffsets != NULL && suboffsets[i] >= 0) ... If suboffsets are consistently NULL, at least hopefully you get branch prediction to kick in. As Sebastian pointed out, it's relatively easy even for slicing/indexing functions to check for all-negative suboffsets and handle that case. All this is probably academic, since no one appears to be using suboffsets at all. :) Let's keep the status-quo and make this a doc issue for 2.7. ---------- assignee: -> docs@python components: +Documentation -Interpreter Core nosy: +docs@python priority: normal -> low stage: patch review -> title: PyBuffer_IsContiguous() sometimes returns wrong result if suboffsets != NULL -> Document "suboffsets if needed" in 2.7 type: behavior -> enhancement _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue23352> _______________________________________