class Foo(object):
  x=1.5
foo=Foo()
print foo.x#通过实例访问类属性
>1.5
print Foo.x #通过类访问类属性
>1.5
foo.x=1.7  #只改新实例属性，不会改变类属性
print foo.x
>1.7
print Foo.x
>1.5
foo.x+=0.2 ##只改新实例属性，不会改变类属性
print foo.x
>1.9
print Foo.x
>1.5
del foo.x ##删除更新的实例属性，默认变为类的属性
print foo.x
>1.5
print Foo.x
>1.5

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

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

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