Getting the dtype of a result array in numpy

Question

I want to preallocate memory for the output of an array operation, and I need to know what dtype to make it. Below I have a function that does what I want it to do, but is terribly ugly.

import numpy as np

def array_operation(arr1, arr2):
    out_shape = arr1.shape
    # Get the dtype of the output, these lines are the ones I want to replace.
    index1 = ([0],) * arr1.ndim
    index2 = ([0],) * arr2.ndim
    tmp_arr = arr1[index1] * arr2[index2]
    out_dtype = tmp_arr.dtype
    # All so I can do the following.
    out_arr = np.empty(out_shape, out_dtype)

The above is pretty ugly. Does numpy have a function that does this?

Answer 1

You are looking for numpy.result_type.

(As an aside, do you realize that you can access all multi-dimensional arrays as 1d arrays? You don't need to access x[0, 0, 0, 0, 0] -- you can access x.flat[0].)