Help in using introspection to simplify repetitive code

[jsceballos@gmail.com]

Hello.
I'm writing a proxy class, i.e: a class whose methods mostly delegate
their functionality to other class object. Most of the methods (which
are quite a lot) defined in the class would end up being:

def thisIsTheMethod Name(self):
self._handlerCl ass.thisIsTheMe thodName()

The handler object is the same in all methods.

I was wondering if there is a way to simplify this proxy class, maybe
using some pythonic technique like metaclasses, introspection.. . any
suggestion is appreciated.

Thanks,

Javier Sanz

[Simon Percivall]

Re: Help in using introspection to simplify repetitive code


jsceballos@gmai l.com wrote:

Hello.
I'm writing a proxy class, i.e: a class whose methods mostly delegate
their functionality to other class object. Most of the methods (which
are quite a lot) defined in the class would end up being:
>
def thisIsTheMethod Name(self):
self._handlerCl ass.thisIsTheMe thodName()
>
The handler object is the same in all methods.
>
I was wondering if there is a way to simplify this proxy class, maybe
using some pythonic technique like metaclasses, introspection.. . any
suggestion is appreciated.
>
Thanks,
>
Javier Sanz

http://docs.python.org/ref/attribute-access.html#l2h-206

[Terry Reedy]

Re: Help in using introspection to simplify repetitive code


<jsceballos@gma il.comwrote in message
news:1156090845 .875872.41220@7 5g2000cwc.googl egroups.com...

Hello.
I'm writing a proxy class, i.e: a class whose methods mostly delegate
their functionality to other class object. Most of the methods (which
are quite a lot) defined in the class would end up being:
>
def thisIsTheMethod Name(self):
self._handlerCl ass.thisIsTheMe thodName()

Are these parameterless static methods
or should this be self._handlerCl ass.thisIsTheMe thodName(self)
or does self get auto-bound even though not a _handlerClass instance?
(I have never needed or done such delegation.)

The handler object is the same in all methods.
>
I was wondering if there is a way to simplify this proxy class, maybe
using some pythonic technique like metaclasses, introspection.. . any
suggestion is appreciated.

My immediate thought would be to start with

_forwarded = set(......) # of forwarded method names
def __getattr__(sel f, name):
if name in _forwarded: return getattr(self._h andlerClass, name)

but I am not sure if this gives the right wrapping and binding.

Terry Jan Reedy

[jsceballos@gmail.com]

Re: Help in using introspection to simplify repetitive code

As you mention, wether the methods take arguments or not is something
to have into account.
And they do take arguments, and a variable number of them, so AFAIK
hooking with __getattr__ or __getattribute_ _ will not work, as you can
only get the method name with that. I was thinking of some __call__
overriding, but I've never done it before and I don't know if this
could be the way to go.
--


Un saludo,

Javier

[Fredrik Lundh]

Re: Help in using introspection to simplify repetitive code

jsceballos@gmai l.com wrote:

And they do take arguments, and a variable number of them, so AFAIK
hooking with __getattr__ or __getattribute_ _ will not work, as you can
only get the method name with that.

why not just return the bound method *object* (a callable), and let the
caller call that as usual (see Terry's last example).

(hint: x.foo() can be written f=getattr(x,"fo o"); f())


</F>

[Tim N. van der Leeuw]

Re: Help in using introspection to simplify repetitive code


Fredrik Lundh wrote:

jsceballos@gmai l.com wrote:
>

And they do take arguments, and a variable number of them, so AFAIK
hooking with __getattr__ or __getattribute_ _ will not work, as you can
only get the method name with that.

>
why not just return the bound method *object* (a callable), and let the
caller call that as usual (see Terry's last example).
>
(hint: x.foo() can be written f=getattr(x,"fo o"); f())
>
>
</F>

I can tell you from my experience that this works; I've used this
before to make something very much like this proxy-class:

class RequestCalculat ions(object):
def __init__(self, request):
self.serviceTyp e, self.facade =
makeMessageFaca deInstance(requ est)
return

def __getattr__(sel f, name):
return getattr(self.fa cade, name)

(rest of the code omitted)

Cheers,

--Tim

[Bruno Desthuilliers]

Re: Help in using introspection to simplify repetitive code

jsceballos@gmai l.com a écrit :

As you mention, wether the methods take arguments or not is something
to have into account.
And they do take arguments, and a variable number of them, so AFAIK
hooking with __getattr__ or __getattribute_ _ will not work, as you can
only get the method name with that.

Nope. Defining __getattr__ is the canonical pythonic way to do
delegation. Remember that in Python, functions and methods are objects
too and can be passed around/returned etc just like any other object.