I'd like input from anyone interested in the following syntax questions. The current experimental Cython syntax for efficient ndarray indexing looks like this: cdef numpy.ndarray[numpy.int64, 2] arr Issue 1: One can argue that "2" above looks like a length specifier to newcomers. Issue 2: This clashes with some forms of C array notation (you can do "sizeof(int[3])" or "extern ... def myfunc(int[])" in Cython, and though such syntax is redundant it will stay in order not to break code). Solving issue #1 helps with #2 as well because without a single integer literal in it it should look a lot less like an array declaration. So, some quick proposals: - Require a "D" suffix for the number of dimensions. This should make it very clear that the 2 stands for dimensionality and not shape. cdef numpy.ndarray[numpy.int64, 2D] arr Variations: a) numpy.ndarray[numpy.int64, 2D] b) numpy.ndarray[numpy.int64 2D] c) numpy.ndarray[2D numpy.int64] (Note that I want to leave the way open for adding mode="c" or mode="fortran", so using a "," seems good for that reason). - Require an ndim keyword: cdef numpy.ndarray[numpy.int64, ndim=2] - Other type of brackets. This boils down to (for various reasons) the <> brackets: cdef numpy.ndarray<numpy.int64, 2> (However, one should remember that Cython may want to support using C++ templates at some point). -- Dag Sverre