Initializes a 2D list of given width and height and value.

Use list comprehension and range() to generate h rows where each is a list with length h, initialized with val. If val is not provided, default to None.

def initialize_2d_list(w,h, val = None):
  return [[val for x in range(w)] for y in range(h)]

initialize_2d_list(2, 2, 0) # [[0,0], [0,0]]