Ejemplo de dectools

gistfile1.py

 @post("self.name and self.price >= 0 and Item.tax_rate >= 0", globals())
    def __init__(self, name, price):
        self.name = name
        self.price = price

    def _invariant(self):
        assert self.name not in ("Swiss", "Cheddar")
        assert self.price > 0

    @pre("adjustment < 0")
    def adjust_price(self, adjustment):
        self.price += adjustment