input: Write a python function to calculate the sum of all elements in a 2D list.
  assert calculate_sum([[1,2,3], [4,5,6], [7,8,9]]) == 45
  assert calculate_sum([[0,0,0], [0,0,0], [0,0,0]]) == 0
  assert calculate_sum([[1,1,1], [1,1,1], [1,1,1]]) == 9
output: def calculate_sum(matrix):
      return sum(sum(row) for row in matrix)