[Numpy-discussion] Cython/NumPy syntax

[Dag Sverre Seljebotn]

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