Numpy: Joining structured arrays?

Input

I have many numpy structured arrays in a list like this example:

import numpy

a1 = numpy.array([(1, 2), (3, 4), (5, 6)], dtype=[('x', int), ('y', int)])

a2 = numpy.array([(7,10), (8,11), (9,12)], dtype=[('z', int), ('w', float)])

arrays = [a1, a2]

Desired Output

What is the correct way to join them all together to create a unified structured array like the following?

desired_result = numpy.array([(1, 2, 7, 10), (3, 4, 8, 11), (5, 6, 9, 12)],
                             dtype=[('x', int), ('y', int), ('z', int), ('w', float)])

Current Approach

This is what I'm currently using, but it is very slow, so I suspect there must be a more efficent way.

from numpy.lib.recfunctions import append_fields

def join_struct_arrays(arrays):
    for array in arrays:
        try:
            result = append_fields(result, array.dtype.names, [array[name] for name in array.dtype.names], usemask=False)
        except NameError:
            result = array

    return result