input: Write a python function to safely divide two numbers, returning 'undefined' if division by zero is attempted.
  assert divide_numbers(10, 2) == 5
  assert divide_numbers(10, 0) == 'undefined'
  assert divide_numbers(9, 3) == 3
output: def divide_numbers(a, b):
      try:
          return a / b
      except ZeroDivisionError:
          return 'undefined'