This method works for any mapping:
month2quarter = {
1:1,2:1,3:1,
4:2,5:2,6:2,
7:3,8:3,9:3,
10:4,11:4,12:4,
}.get
We have just generated a function int->int
month2quarter(9) # returns 3
This method is also fool-proof
month2quarter(-1) # returns None
month2quarter('July') # returns None