python中添加方法，等等

Functions are descriptors, and their __get__ method is used to bind
them to a particular instance::
     >>> class test(object):
     ...     def __init__(self):
     ...         pass
     ...
     >>> x = test()
     >>> def fun(self):
     ...     print "fun", self
     ...
     >>> x.fun = fun.__get__(x, test)
     >>> x.fun()
     fun  
Note that calling __get__ returns a bound method, and that method can be
bound to an instance or a class depending on the parameters of __get__::
     >>> fun.__get__(x, None)
     >
     >>> fun.__get__(x, test)
     >
     >>> fun.__get__(None, test)
     

Injecting a method into a class, so that even already-created instances
have that method, is trivial:
>>> class K(object):
...     pass
...
>>> def fun(self, arg):
...     print "fun"
...     self.frob = arg
...
>>> o = K()
>>> K.methc = fun
>>> o.methc("xyz")
fun
>>> o.frob
'xyz'
>>>
Injecting a "private" method into a particular instance is not much more
complicated:
>>> def own(self, arg):
...    print "own"
...    self.ozz = arg
...
>>> p = K()
>>> import types
>>> p.metho = types.MethodType(own, p)
>>> p.metho("plugh")
own
>>> p.ozz
'plugh'
>>> o = K()
>>> o.metho("xyzzy")
Traceback (most recent call last):
   File "", line 1, in ?
AttributeError: 'K' object has no attribute 'metho'
>>>