Using descriptors to wrap methods

[Edward C. Jones]

Here is a stripped-down version of a Python Cookbook recipe. Is there a
simpler, more Pythonical, natural way of doing this?

------
#! /usr/bin/env python

# Modified from Python Cookbook entry 91192, "eiffelmeth od" by Andres
# Tuells. The url is
# http://aspn.activestate.com/ASPN/Coo...n/Recipe/91192

class MethodWraper(ob ject):
def __init__(self, method):
self.method = method
def __get__(self, inst, type=None):
result = wrapper(inst, self.method)
setattr(inst, self.method.__n ame__, result)
return result

class wrapper:
def __init__(self, inst, method):
self.instance = inst
self.method = method

def __call__(self, *args, **kargs):
print 'pre'
result = apply(self.meth od, (self.instance, ) + args, kargs)
print 'post'
return result

def test():
class C:
def f(self, arg):
print 'in f'
return arg+1
f = MethodWraper(f)

c = C()
print c.f(1)

if __name__=='__ma in__':
test()
------

[Duncan Booth]

Re: Using descriptors to wrap methods

"Edward C. Jones" <edcjones@erols .com> wrote in
news:408cfa5a$0 $28920$61fed72c @news.rcn.com:
[color=blue]
> Here is a stripped-down version of a Python Cookbook recipe. Is there a
> simpler, more Pythonical, natural way of doing this?[/color]

Here's a simpler way of doing the same thing:
[color=blue][color=green][color=darkred]
>>> def MethodWrapper(f ):[/color][/color][/color]
def wrapper(self, *args, **kw):
print 'pre'
result = f(self, *args, **kw)
print 'post'
return result
return wrapper
[color=blue][color=green][color=darkred]
>>> class C(object):[/color][/color][/color]
def f(self, arg):
print 'in f'
return arg+1
f = MethodWrapper(f )

[color=blue][color=green][color=darkred]
>>> c = C()
>>> print c.f(1)[/color][/color][/color]
pre
in f
post
2[color=blue][color=green][color=darkred]
>>>[/color][/color][/color]

Or if you want pre and post code customisable you might try:
[color=blue][color=green][color=darkred]
>>> def MethodWrapper(f , pre=None, post=None):[/color][/color][/color]
def wrapper(self, *args, **kw):
if pre: pre(self, *args, **kw)
result = f(self, *args, **kw)
if post: post(self, result, *args, **kw)
return result
return wrapper
[color=blue][color=green][color=darkred]
>>> class C(object):[/color][/color][/color]
def pre_f(self, arg):
print 'pre',arg
def post_f(self, res, arg):
print 'post',res,arg
def f(self, arg):
print 'in f'
return arg+1
f = MethodWrapper(f , pre_f, post_f)


[color=blue][color=green][color=darkred]
>>> c = C()
>>> c.f(1)[/color][/color][/color]
pre 1
in f
post 2 1
2[color=blue][color=green][color=darkred]
>>>[/color][/color][/color]

I don't know if you could call it Pythonic though.

[Sean Ross]

Re: Using descriptors to wrap methods


"Edward C. Jones" <edcjones@erols .com> wrote in message
news:408cfa5a$0 $28920$61fed72c @news.rcn.com.. .[color=blue]
> Here is a stripped-down version of a Python Cookbook recipe. Is there a
> simpler, more Pythonical, natural way of doing this?
>[/color]

def wrap(f):
def wrapped(*args, **kwds):
print 'pre'
result = f(*args, **kwds)
print 'post'
return result
return wrapped