title: Convert letter grades to grade points via python 3
body: <p>I have a question for transforming a list
  Given: [A,B,C,D,F,W]
  but any letter counts, except W.
  Where A = 4 , B = 3, C = 2, D = 1 and F = 0
  so the final output should be [4, 3, 2, 1, 0]
  can anyone help on this? How to print out the list of [4,3,2,1,0] right after I filter out the letter 'W'? thanks!</p>