old_contents: def add(x, y=None):
      if y != None:
          return x + y
      else:
          def helper(z):
              return x + z
          return helper
  
  print(add(3,4))
  print(add(3)) # prints function
  print(add(3)(4))
  
new_contents: def add(x, y=None):
      if y != None:
          return x + y
      else:
          def helper(z):
              return x + z
          return helper
  
  print(add(3,4))
  print(add(3)) # prints function
  print(add(3)(4))
  
  # named arguments
  print(add(y=7, x=3))
  
subject: add named args