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Newsgroups: comp.lang.python
Date: Fri, 1 Feb 2013 03:26:27 -0800 (PST)
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Subject: Re: confusion with decorators
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Xref: csiph.com comp.lang.python:38037

Jason Swails=E6=96=BC 2013=E5=B9=B41=E6=9C=8831=E6=97=A5=E6=98=9F=E6=9C=9F=
=E5=9B=9BUTC+8=E4=B8=8A=E5=8D=888=E6=99=8234=E5=88=8603=E7=A7=92=E5=AF=AB=
=E9=81=93=EF=BC=9A
> Hello,
>=20
>=20
> I was having some trouble understanding decorators and inheritance and al=
l that. =C2=A0This is what I was trying to do:
>=20
>=20
>=20
> # untested
> class A(object):
> =C2=A0 =C2=A0def _protector_decorator(fcn):
>=20
> =C2=A0 =C2=A0 =C2=A0 def newfcn(self, *args, **kwargs):
> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0return fcn(self, *args, **kwargs)
> =C2=A0 =C2=A0 =C2=A0 return newfcn
>=20
>=20
>=20
> =C2=A0 =C2=A0@_protector_decorator
> =C2=A0 =C2=A0def my_method(self, *args, **kwargs):
> =C2=A0 =C2=A0 =C2=A0 """ do something here """
>=20
>=20
>=20
> class B(A):
> =C2=A0 =C2=A0def _protector_decorator(fcn):
> =C2=A0 =C2=A0 =C2=A0 def newfcn(self, *args, **kwargs):
>=20
> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0raise MyException('I do not want B to b=
e able to access the protected functions')
> =C2=A0 =C2=A0 =C2=A0 return newfcn
>=20
>=20
>=20
> The goal of all that was to be able to change the behavior of my_method i=
nside class B simply by redefining the decorator. Basically, what I want is=
 B.my_method() to be decorated by B._protector_decorator, but in the code I=
'm running it's decorated by A._protector_decorator.
>=20
>=20
>=20
> I presume this is because once the decorator is applied to my_method in c=
lass A, A.my_method is immediately bound to the new, 'decorated' function, =
which is subsequently inherited (and not decorated, obviously), by B.
>=20
>=20
>=20
> Am I correct here? =C2=A0My workaround was to simply copy the method from=
 class A to class B, after which B._protector_decorator decorated the metho=
ds in B. =C2=A0While this doesn't make the use of decorators completely poi=
ntless (the decorators actually do something in each class, it's just diffe=
rent), it does add a bunch of code duplication which I was at one point hop=
eful to avoid.
>=20
>=20
>=20
> I'm still stumbling around with decorators a little, but this exercise ha=
s made them a lot clearer to me.
>=20
>=20
> Thanks!
> Jason

It sounds that you need a decorator mapper to=20
perform the functionality of your designs.