input: Write a function to accept a number from the user and print all its divisors in a comma-separated list. If the input number is negative, the function should return an error message indicating invalid input.
  def find_divisors(num):
      if num < 0:
          return "Invalid input: number must be non-negative"
      divisors = [i for i in range(1, num + 1) if num % i == 0]
      print('The divisors of', num, 'are:', ', '.join(map(str, divisors)))
  
  assert find_divisors(12)=="The divisors of 12 are: 1, 2, 3, 4, 6, 12"
  assert find_divisors(15)=="The divisors of 15 are: 1, 3, 5, 15"
  assert find_divisors(17)=="The divisors of 17 are: 1, 17"
  assert find_divisors(-5)=="Invalid input: number must be non-negative"
  assert find_divisors(0)=="The divisors of 0 are: "
output: def find_divisors(num):
      if num < 0:
          return "Invalid input: number must be non-negative"
      divisors = [i for i in range(1, num + 1) if num % i == 0]
      return 'The divisors of ' + str(num) + ' are: ' + ', '.join(map(str, divisors))