Confused with methods

[jfj]

Hello Diez.
I sent a reply to the previous message requesting an example of
what would break, but unfortunatelly it didn't make it in python-list.
Here it is for the record [
> Diez B. Roggisch wrote:
> 
>>If things worked as you wanted it to, that would mean that passing bound
>>method as argument to a class and storing it there to an instance variable
>>that would "eat up" the arguments - surely not the desired behaviour.
> 
> 
> Could you please give an example of this ?
> 
> If you mean:
> 
>    class A:
>       def f(x):
>          print x
> 
>    class B:
>       pass
> 
>    a=A()
>    B.f = a.f
>    b=B()
>    b.f()     #surprise: it works!!
> 
> then that is equally "weird" as my case. "eat up" sounds
> rather bad but all what will happen is an argument number
> mismatch.
> In fact is seems more appropriate to use a.f.im_func in this
> case to "convert the bound method to an unbound one".
> 
> Maybe this happens more often?
> 
> 
> Thanks,
> 
> G.
> 
]

Diez B. Roggisch wrote:

>>If there a good reason that the __get__ of a boundmethod does not
>>create a new boundmethod wrapper over the first boundmethod?
> 
> 
> I already gave you the good reason:
> 
> class A:
>    def callback(self, arg):
>        print self, arg
> 
> def callback(arg):
>     print arg
> 
> class DoSomethingWithCallback:
>     def __init__(self, cb):
>         self.cb = cb
> 
>     def run(self):
>         for i in xrange(100):
>              self.cb(i)
> 
> u = DoSomethingWithCallback(A().callback)
   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Oops!!!
I think it would be more obvious to somebody who doesn't know
the python internals, to say:
  # take the callback from A and install it to DSWC
  u=DoSomethingWithCallback( A.callback)
or
  u=DoSomethingWithCallback (A().callback.im_func)
or
  u=DoSomethingWithCallback (A().im_class.callback)


> v = DoSomethingWithCallback(callback)
> 
> # would crash if your suggestion worked
> u.run()
> v.run()
> 

It would complain about not enough arguments.
As it does in the case I'm confused about!

> If you are after currying - look at the cookbook, there are recipes for
> that.

I'm satistfied with Alex's response that it is like that for backwards
compatibility, but in Python 3000 it may be the other way around.


Thanks all.

jfj