input: Write a function to convert a given string to a list of integers by splitting the string by commas and converting each split part to an integer.
  
  def to_int_list(s):
      return [int(x) for x in s.split(',')]
  
  assert to_int_list("1,2,3,4,5")==[1,2,3,4,5]
  assert to_int_list("10,20,30")==[10,20,30]
  assert to_int_list("5,10,15,20")==[5,10,15,20]
  assert to_int_list("1,3,5,7,9")==[1,3,5,7,9]
  assert to_int_list("")==[]
output: def to_int_list(s):
      return [int(x) for x in s.split(',')]