Sometimes I just want to monkeypatch the list to be immutable in my app.

  def make_pizza(crust=THIN, toppings=[], cheese=REGULAR, sauce=TOMATO):
    // first call: toppings=["peperoni"]
    // second call: toppings=["peperoni", "sausage"]
    // third call: toppings=["peperoni", "sausage"]

  make_pizza(toppings=["peperoni"])
  make_pizza(toppings=["sausage"])
  make_pizza()