divide list ['a', 'b', 'c', '1', '2', '3'] into three separate list

def separate_list(list):
  list_length = len(list)
  first_list_length = int(list_length/3)
  first_list = list[:first_list_length]
  second_list = list[first_list_length:first_list_length*2]
  third_list = list[first_list_length*2:]
  return first_list, second_list, third_list