title: How to calculate Standard Deviation using loops on Python
body: <p>I have to calculate the standard deviation using loops for a list. 
  This is what I have: </p>
  
  <pre><code>elif user_option == 2:
    stdev= 0
    average = 0
    for val in scores_list:
      diffsquared= (val - average)**2
      sum_diffsquared= diffsquared + val
      stdev= ((sum_diffsquared)/num_scores)**(1/2)
      print(stdev)
  </code></pre>
  
  <p>I keep on getting the wrong number.</p>