If you are going to introduce this functionality, please don't call it np.arr.

Right now, np.a<tab> presents you with a whopping 53 completion choices.  Adding "r", narrows that to 21, but np.arr<tab> completes to np.array right away.  Please don't introduce another bump in this road.

"Namespaces are one honking great idea -- let's do more of those!"

I would suggest calling it something like np.array_simple or np.array_from_string, but the best choice IMO, would be np.ndarray.from_string (a static constructor method).