17.4.py

#coding:utf-8

class Kangaroo(object):

    def __init__(self,pouch_contents=[]):
        self.pouch_contents = pouch_contents

    def put_in_pouch(self,obj):
        self.pouch_contents.append(obj)

        def __str__(self):
            t = [object.__str__(self) + ' with pouch contents:']
            for obj in self.pouch_contents:
                s = '    ' + object.__str__(obj)
                t.append(s)
            return '\n'.join(t)

kanga = Kangaroo()
roo = Kangaroo()

kanga.put_in_pouch('wallet')
kanga.put_in_pouch('cookies')
kanga.put_in_pouch(roo)

print kanga
print roo

print kanga.pouch_contents is roo.pouch_contents
print kanga.pouch_contents == roo.pouch_contents