Just checked my understanding of the documentation: we pass arrays by reference to python. Modified example from this thread
using PyCall
py"""
import numpy
xs = numpy.zeros((2, 2))
"""
xs = PyArray(py"xs"o)
println(xs)
py"""
import numpy
xs[0, 0] = 1
"""
println(xs)
resolves to
[0.0 0.0; 0.0 0.0]
[1.0 0.0; 0.0 0.0]
But of course you are out of luck if Python generates the array.