input: Write a function to generate a countdown from a given positive integer and print each number in the sequence using a while loop. The function should print "Done!" after the countdown is complete.
  
  def countdown(num):
      while num > 0:
          print(num)
          num -= 1
      print("Done!")
  
  # Test cases
  countdown(6)  # Expected output: 6, 5, 4, 3, 2, 1, Done!
output: def countdown(num):
      while num > 0:
          print(num)
          num -= 1
      print("Done!")