title: how to combine 2D arrays into a 3D array in python?
body: <p>I have a project in which there is a for loop running about 14 times. In every iteration, a 2D array is created with this shape (4,3). I would like to concatenate those 2D arrays into one 3D array (with the shape of 4,3,14) so that every 2D array would be in different "layer". 
  How should that be implemented in Python?</p>