类继承（Python）输出问题

Question

I'm going through 'Learning Python The Hard Way', and I got to the class lesson. I understood it (or I at least think I did!) and tried to create a simple variation, using my own names, functions, etc...

Now the problem I'm having is that the code won't return anything in command line\\powershell. It doesn't have any errors, it just goes to another line of input.

Here's the Code:

class Animal(object):
    '''represents any animal'''
    def __init__(self, legs, size):
        self.legs = legs
        self.size = size

    def detail_animal(self):
        '''show # of legs and size'''
        print "Name: %r\nAge: %r" % (self.legs, self.size)

class canine(Animal):   
    '''represents a canine'''

    def __init__(self, legs, size, hair_length):
        Animal.__init__(self, legs, size)
        self.hair_length = hair_length

    def detail_canine(self):
        Animal.detail(self)
        print 'Has %r inch long hairs.' % self.hair_length

class feral_cat(Animal):
    '''represents a feral cat'''

    def __init__(self, legs, size, tail_length):
        Animal.__init__(self, legs, size)
        self.tail_length = tail_length

    def detail_feral(self):
        Animal.detail(self)
        print "Tail Length: %r" % tail_length

c1 = canine(4, 2, 0.5)
c2 = canine(5, 3, 0.75)
fc1 = feral_cat(4, 5, 3)
a = Animal(4, 2)

Thanks in advance!

Answer 1

There are a few problems in your code: the Animal class doesn't have a method called detail , which you try to call in all its subclasses. You should probably rename detail_animal(self) to detail(self) . To have your program print some output add these lines at the end:

c1.detail_canine()
c2.detail_canine()
fc1.detail_feral()
a.detail()

Furthermore if your program is meant to experiment with method overriding, ie the possibility of redefining base class methods in subclasses, you should try and change detail_canine(self) and detail_feral(self) into detail(self) . Remember to make the change also in the lines I suggested you should add! You'll see that when you instantiate (ie create) an object of the base class Animal 's detail(self) method gets called; when you instantiate one of the subclasses that class's detail(self) method gets called instead.