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getbuffer() checks that the buffer is contiguous. "s#", "y", "z" formats use convertbuffer() which doesn't check that the buffer is contigious, as "w" and "w#" formats which call directly PyObject_GetBuffer() which extra check.
I don't think that the functions using these format support discontiguous buffers. I cannot check because I don't know how to create such buffer. It would be safer to reject discontigious buffer.
If a function would like to support discontigious buffer, it should use "O" format, call PyObject_GetBuffer() with the right option and do its own checks on the buffer object.