On 2/8/06, Delaney, Timothy (Tim) <[EMAIL PROTECTED]> wrote: > limodou wrote: > > > On 2/8/06, adam johnson <[EMAIL PROTECTED]> wrote: > >> Thanks for you answer. > >> > >> I was under the impression that you could tack methods onto an > >> object at any time, your example almost works with old style classes > >> and would with a function instead of a method. > > In fact it will work if you change the A.hello to self.hello ... > > class A: > > def __init__(self): > self.__call__ = self.hello > > def hello (self): > print 'Hello, world!' > > a = A() > a() > > Hello, world! > > >> So now all I need to know is why now with new style classes the > >> special functions need to be defined on the class instead of > >> attached to the instance at any time. > > http://users.rcn.com/python/download/Descriptor.htm > > > don't need do like above! > > > > >>> class A: > > ... def __init__(self): > > ... A.__call__ = A.hello > > ... def hello(self): > > ... print "Hello, world!" > > > > >>> a = A() > > >>> a() > > Hello, world! > > > > You should review the bound method and unbound method. > > This has nothing to do with it - in the above example, you are setting > the *class* attribute of a user-defined class (which allows setting > additional attributes) - which therefore makes instances callable. > Of course I know that.
> Compare the equivalent for the current module: > > import sys > > def hello (self): > print 'Hello, world!' > > m = sys.modules[__name__] > mc = type(m) > mc.__call__ = hello > > Traceback (most recent call last): > File "D:\Python\modules\testclasscall.py", line 7, in ? > mc.__call__ = hello > TypeError: can't set attributes of built-in/extension type 'module' > The exception is right, some special method cannot be replace for some built-in type(new-style class). I just don't suggest adding __call__() to a module, I don't know why does he need this. Because I think the module normally works like a namespace. -- I like python! My Blog: http://www.donews.net/limodou NewEdit Maillist: http://groups.google.com/group/NewEdit -- http://mail.python.org/mailman/listinfo/python-list
