title: Slicing a 20×20 area around known indices (x, y) in a numpy array
body: <p>I have a large 2D numpy array for which I know a pair of indices which represent one element of the array. I want to set this element and the surrounding 20×20 area equal to zero; I have attempted using a slicing technique:</p>
  
  <pre><code>s = array[x:10, y:10]
  s == 0
  </code></pre>
  
  <p>However, although x and y are previously defined, this is an 'invalid slice'.</p>
  
  <p>I would appreciate any suggestions as to how I can accomplish this as I am new to Python.</p>