title: how to extract required dimension from a numpy array
body: <p>Given that I have a numpy array of three dimension [3,500,500], how can I extract one dimension as [1,500,500]?</p>
  
  <pre><code>import numpy as np
  my_array = np.ones((3,500,500),dtype=int,order='C')
  print (my_array)
  </code></pre>