[Edu-sig] More on decorators

[kirby urner]

>  I do use staticmethod, and I've got some good examples at http://ece.arizona.edu/~edatools/Python/Animals.py, but never saw a real need for classmethod.  Your example at least makes the utility plausible, although I could easily do the same without a classmethod.  But I think I see what you are trying to do.  Maybe you could expand the example a bit to make it more compelling.  In the current example, the variable klass has only one value, Register.  You could have multiple classes (Retail, Wholesale, etc.) to drive home that klass really is an important variable, and can't just be hard-coded as Register.
>

Hi Dave --

Good questions!

I think the staticmethod vs. classmethod topic, decorators aside,
is a good one, I hope we do more on it.

Here's your Animals.py with classmethod in place of staticmethod.
Works about the same.  But I won't say "this answers your question"
-- just adds more grist to the mill at this point.

class Animal(object):
    "Ancestor of the Animal hierarchy"
    _numAnimals = 0
    home = "Earth"
    def __init__(self):
        Animal._numAnimals += 1
    @classmethod
    def show(klass):
        print "Inventory:"
        print " Animals:", klass._numAnimals

class Reptile(Animal): pass

class Mammal(Animal):
    _numMammals = 0
    basal_metabolic_rate = 7.2
    def __init__( self, s = "Maa... Maa..."):
        Animal.__init__(self)
        Mammal._numMammals += 1
        self.sound = s
    @classmethod
    def show(klass):
        Animal.show()
        print " Mammals:", klass._numMammals,
        print "        BMR =", klass.basal_metabolic_rate
    def talk(self):
        print "Mammal sound: ", self.sound

class Bovine(Mammal): pass

class Canine(Mammal): pass

class Feline(Mammal):
    _numFelines = 0
    genus = "feline"
    def __init__( self):
        Mammal.__init__(self)
        Feline._numFelines += 1
    @classmethod
    def show(klass):
        Mammal.show()
        print " Felines:", klass._numFelines

class Cat(Feline):
    _numCats = 0
    def __init__( self, n = "unknown", s = "Meow" ):
        Feline.__init__(self)
        Cat._numCats += 1
        self.name = n
        self.sound = s
    @ classmethod
    def show(klass):
        Feline.show()
        print "    Cats:", klass._numCats

    def talk(self):
        print "My name is ...", self.name
        print "I am a %s from %s" % (self.genus, self.home)
        Mammal.talk(self)

def test():
    a = Animal()
    m = Mammal(); print "m:",; m.talk()
    f = Feline(); print "f:",; f.talk()
    c = Cat();    print "c:",; c.talk()
    print "--- Cat.show() ---"
    Cat.show()
    print "--- cat1.talk() ---"
    cat1 = Cat("Garfield", "Purr")
    cat1.talk()

if __name__ == '__main__':
    test()

Kirby