input: 
  Write a function to convert a given string to a list of integers. The string is assumed to be comma-separated, with no spaces between the commas and the numbers. The function should return a list of integer values corresponding to the numbers in the input string.
  
  def to_int_list(s):
      return [int(x) for x in s.split(',')]
  
  assert to_int_list("1,2,3,4")==[1, 2, 3, 4]
  assert to_int_list("10,20,30")==[10, 20, 30]
  assert to_int_list("0,0,0,0")==[0, 0, 0, 0]
  assert to_int_list("1")==[1]
  assert to_int_list("")==[]
output:     
      return [int(x) for x in s.split(',') if x]
  