python 3.x - Making a 2D grid with two arrays (x,y) and corresponding values from a third array (z) -

i have 3 1d arrays(lists) in following format (example):

x = [10,10,10,20,20,20,30,30,30] y = [3.2,3.6,3.9,3.2,3.6,3.9,3.2,3.6,3.9] z = [21,25,35,45,41,32,23,47,28] 

i want create grid x , y being 2d grid in shape of 3x3 (actually need larger grid, concept matters). , each of 9 cells in 3x3 grid need appoint value z (example):

to cell x,y = (10, 3.2) first value of z (21) , on.... straitforward , in end have read want make contour plot, cannot figure out right procedure.

thanks in advance solution.