Question

How can I create an array in shared memory without modifying the kernel using templates as seen in the official examples. Or is using templates the official way?

In PyOpenCL I can create an array in local memory with setting a kernel argument

kernel.set_arg(1,numpy.uint32(a_width))

... 
KERNEL_CODE = """
__kernel void matrixMul(__local float* A_temp,...)
    { ...} """

Answer 1

CUDA supports dynamic shared memory allocation at kernel run time, but the mechanism is a bit different to OpenCL. In the CUDA runtime API, a kernel using dynamically allocated/sized shared memory and the launch to size the memory uses the following syntax:

__global__ void kernel(...)
{
    extern __shared__ typename buffer[];

    ....
}
....
kernel <<< griddim, blockdim, sharedmem, streamID >>> (...)

where sharedmem is the total number of bytes per block which will be allocated to buffer.

In PyCUDA, the same mechanism works something like this:

mod = SourceModule("""
    __global__ void kernel(...)
    {
        extern __shared__ typename buffer[];

        ....
    }
  """)

func = mod.get_function("kernel")
func.prepare(..., shared=sharedmem)
func.prepared_call(griddim,blockdim,...)

with the shared memory allocation size passed to the prepare method.