On 01/30/2013 07:34 PM, Jason Swails wrote:
Hello,
I was having some trouble understanding decorators and inheritance and all
that. This is what I was trying to do:
# untested
class A(object):
def _protector_decorator(fcn):
def newfcn(self, *args, **kwargs):
return fcn(self, *args, **kwargs)
return newfcn
@_protector_decorator
def my_method(self, *args, **kwargs):
""" do something here """
class B(A):
def _protector_decorator(fcn):
def newfcn(self, *args, **kwargs):
raise MyException('I do not want B to be able to access the
protected functions')
return newfcn
The goal of all that was to be able to change the behavior of my_method
inside 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.
I presume this is because once the decorator is applied to my_method in
class A, A.my_method is immediately bound to the new, 'decorated' function,
which is subsequently inherited (and not decorated, obviously), by B.
Am I correct here? My workaround was to simply copy the method from class
A to class B, after which B._protector_decorator decorated the methods in
B. While this doesn't make the use of decorators completely pointless (the
decorators actually do something in each class, it's just different), it
does add a bunch of code duplication which I was at one point hopeful to
avoid.
I'm still stumbling around with decorators a little, but this exercise has
made them a lot clearer to me.
I'm certainly not the expert on decorators; I've only used them for
simple things. But I think I can clear up one misconception.
The decorator function will execute while *compiling* the class A, and
the one in class B is unreferenced.
The decorator @_protector_decorator is shorthand for something like
mymethod = _protector_decorator(mymethod)
So by the time the compiler ends with class A, the mymethod has its
final value.
(Note, I've not used a decorator that was defined inside a class, so I'm
probably missing the appropriate A. or self. or cls. overrides.)
But the order of definition is still correct. A decorator executes
once, just after a function is completed.
--
DaveA
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