title: Modify a specific x-axis tick label in python
body: <p>I am an undergrad newbie to the Python pyplot. What I want to do is to plot a function against a sequence, for example, <code>x = [1,2,3,4,5]</code>. </p>
  
  <p>The <code>pyplot.plot</code> function naturally gives a nice figure. But I want to replace on the x-axis the tick label "2" by a string say "key point" and at the same time make the tick labels, for example, "4" and "5" invisible. How can I achieve this in <code>pyplot</code>? </p>
  
  <p>Your help will be highly appreciated.  </p>