input: Write a function to add two numbers together and print the result. The function should take two arguments, `a` and `b`, and return the sum of these two numbers. If either of the arguments is not a number, the function should raise a `TypeError`. 
  
  assert add(5, 7)==12
  assert add(-1, -1)==-2
  assert add(0, 0)==0
  assert add(3.5, 2.5)==6.0
  try:
      add('a', 7)
  except TypeError:
      pass
  else:
      assert False
output: def add(a, b):
      if not isinstance(a, (int, float)) or not isinstance(b, (int, float)):
          raise TypeError
      return a + b