module with __call__ defined is not callable?

[limodou]

On 2/8/06, Delaney, Timothy (Tim) <tdelaney at avaya.com> wrote:
> limodou wrote:
>
> > On 2/8/06, adam johnson <adam.sven.johnson at gmail.com> 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.

--
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