【python】class之子类

父类：

 class AddrBookEntry(object):
    "address book entry class"
    def __init__(self, nm, ph):
        self.name = nm
        self.phone = ph
        print "created instance for:", self.name
    def updatePhone(self, newph):
        self.phone = newph
        print "updated phone# for:", self.name

子类：

当一个类被派生出来，子类就继承了基类的属性。所以EmplAddrBookEntry继承了AddrBookEntry的updatePhone的方法。子类最好自定义自己的构造器，不然基类的构造器会被调用。如果子类重写了基类的构造器，基类的构造器就不会自动调用，除非被显示声明出来。

class EmplAddrBookEntry(AddrBookEntry):
    "employee address book entry class"
    def __init__(self, nm, ph, id, em):##重写基类构造器
        AddrBookEntry.__init__(self, nm, ph)
        self.empid = id
        self.email = em
    def updateEmail(self, newem):
        self.email = newem
        print "updated e-mail address for:", self.name

使用子类：

john = EmplAddrBookEntry("john doe","408-555-1212", 42, "[e-mail]")
created instance for: john doe
>>> john
<__main__.EmplAddrBookEntry object at 0x02115FD0>
>>> john.name
'john doe'
>>> john.phone
'408-555-1212'
>>> john.email
'[e-mail]'
>>> john.updatePhone("415-555-1212")
updated phone# for: john doe
>>> john.phone
'415-555-1212'
>>> john.updateEmail("[e-mail]")
updated e-mail address for: john doe
>>> john.email
'[e-mail]'