title: calculation of variance function equation
body: <p>I have an error in this code as I want to calculate the variance between the values in the(x1) and (x2) list. any recommendation?!</p>
  
  <pre><code>def my_var(L):
      s = 0
      t = 0
      u = 0
      for i in range(0, len(L)):
          s += L[i]
          t = s/len(L)
          u += ((L[i]-t)*(L[i]-t))
      return u / len(L)
  x1 = [1, 3, 4, -3, 8]
  x2 = [1, -4, 7, 2]
  v1 = my_var(x1)
  v2 = my_var(x2)
  print(v1)
  print(v2)
  </code></pre>