Referring to method of a class without instance?

[Daniel Berlin]

gmol at my-deja.com writes:


> In my application I use the observer/observable pattern..question
> I hate duplicating the information of what was changed by making up a
> new message type (global message variables or strings) and using tonnes
> of if-else clauses.  I'd rather just tell my observer which method was
> called and the arguments passed to it.  (I.e. I have atoms in 3d space,
> when setPosition(position) is called I would just like to tell whoever
> is interested that setPosition was called with the argument position))
> 
> Problem, how do I refer to the method of a given class without making an
> instance?  Like suppose I notify my observers by giving the funciton
> address and arguments, I would like the observer to have a dictionary
> whose keys are methods
> 
> class Atom:
> ....
> 
> 
> class myobserver:
> ...
> 
>    updateTable={....
>        Atom.setPosition:handle_A_setPositio
>     }
> ...
> 
> Hmm I have also just realized that given
> class A:
>  def __init__(self...)
> 
> a=A()
> 
> a.init is not equal to A.__methods__['__init__']
> 
> Hmmm I thought that would be the worst way I could do it, but I guess I
> couldn't if I wanted to...
> 
> Any thoughts or better general solution would be appreciated...
>


This is a simple problem.

Try A.__init__
>>> class B:
...     def __init__(self):
...             pass
...
>>> B.__init__
<unbound method B.__init__>
>>>               __

If you try to call it without a class instance as the first parameter, you'll get an error.

>>> B.__init__(5)
Traceback (innermost last):
  File "<stdin>", line 1, in ?
TypeError: unbound method must be called with class instance 1st argument

Otherwise, it'll work fine.

>>> B.__init__(B())  

HTH,
Dan