Wrapping a method twice

[Nicolas Girard]

Hi all,
given the following code:

---
def append(method,b ottom):
def wrapped(*args, **kwargs):
res = method(*args, **kwargs)
return bottom(res,*arg s, **kwargs)
setattr(method. im_class,method .__name__,wrapp ed)

def prepend(method, top):
def wrapped(*args, **kwargs):
top(*args, **kwargs)
return method(*args, **kwargs)
setattr(method. im_class,method .__name__,wrapp ed)


def test():
class C:
def f(self):
print "f"

def pre(self):
print "pre"

def post(res,self):
print "post"

prepend(C.f,pre )
append(C.f,post )
C().f()
---

how comes that test() only outputs:

pre
f

rather than what I expected:

pre
f
post

Thanks very much in advance,
cheers,
Nicolas

[marek.rocki@wp.pl]

Re: Wrapping a method twice

Nicolas Girard napisa³(a):

prepend(C.f,pre )

This wraps f, returns wrapped and binds it to C.f (but the
method.__name__ is still wrapped).

append(C.f,post )

This wraps wrapped (the one previously returned), returns wrapped (a
new one) and binds it to C.wrapped (since that is what its
method.__name__ says).

C().f()

If you try C().wrapped() it works as expected.

So the problem is in retaining the function name. Try:

def append(method,b ottom):
def wrapped(*args, **kwargs):
res = method(*args, **kwargs)
return bottom(res,*arg s, **kwargs)
wrapped.__name_ _ = method.__name__
setattr(method. im_class,method .__name__,wrapp ed)

def prepend(method, top):
def wrapped(*args, **kwargs):
top(*args, **kwargs)
return method(*args, **kwargs)
wrapped.__name_ _ = method.__name__
setattr(method. im_class,method .__name__,wrapp ed)

[Michele Simionato]

Re: Wrapping a method twice

On Jun 25, 1:52 pm, marek.ro...@wp. pl wrote:

>Try:
>
def append(method,b ottom):
    def wrapped(*args, **kwargs):
        res = method(*args, **kwargs)
        return bottom(res,*arg s, **kwargs)
    wrapped.__name_ _ = method.__name__
    setattr(method. im_class,method .__name__,wrapp ed)
>
def prepend(method, top):
    def wrapped(*args, **kwargs):
        top(*args, **kwargs)
        return method(*args, **kwargs)
    wrapped.__name_ _ = method.__name__
    setattr(method. im_class,method .__name__,wrapp ed)

If you are using Python 2.5, consider functools.updat e_wrapper, which
also sets __module__,
__doc__ and other attributes.