Making (500,) array (500,20)
(500,) stands for a array with 500 values,
array (500,20), stands for an array which contains 500 list and each list containing 20 elements.
Examples: 
array(1,2,3,4) ----------------------&gt; (4,)

array([1,2],[3,4],[5,6])-------------&gt; (3,2)