On Thu, 24 Feb 2005 15:00:46 -0700, Steven Bethard
<[EMAIL PROTECTED]> wrote:
> Tom Willis wrote:
> > Question on decorators in general. Can you parameterize those?
> >
> > If I wanted to something and after the function call for example, I
> > would expect something like this would work.
> >
> > def prepostdecorator(function,pre,post):
> > def wrapper(*args,**kwargs):
> > pre()
> > result = function(*args,**kwargs)
> > post()
> > return result
> > return wrapper
> >
> > def dopre():
> > print "call pre"
> >
> > def dopost():
> > print "call post"
> >
> > @prepostdecorator(pre,post)
> > def sayhello(Name):
> > print "Hey %s, nice to meet you" % Name
> >
> > #sayhello = prepostdecorator(sayhello,dopre,dopost)
> >
> > if __name__=="__main__":
> > sayhello("Dude")
> >
> > but I get ...
> > TypeError: prepostdecorator() takes exactly 3 arguments (2 given)
>
> You get this TypeError for the same reason that I get the following
> TypeError:
>
> py> def prepostdecorator(function, pre, post):
> ... pass
> ...
> py> prepostdecorator(1, 2)
> Traceback (most recent call last):
> File "<interactive input>", line 1, in ?
> TypeError: prepostdecorator() takes exactly 3 arguments (2 given)
>
> The expression after @ is a _normal Python expression_. So since you
> couldn't call prepostdecorator with 2 arguments in any other situation,
> you still can't.
>
> If you want to call prepostdecorator with 2 arguments, you need to write
> it this way. A few options:
>
> (1) Use nested functions:
>
> py> def prepostdecorator(pre,post):
> ... def decorator(function):
> ... def wrapper(*args,**kwargs):
> ... pre()
> ... result = function(*args,**kwargs)
> ... post()
> ... return result
> ... return wrapper
> ... return decorator
> ...
> py> @prepostdecorator(dopre, dopost)
> ... def sayhello(name):
> ... print "Hey %s, nice to meet you" % name
> ...
> py> sayhello('Tom')
> call pre
> Hey Tom, nice to meet you
> call post
>
> (2) Use functional.partial (PEP 309[1])
>
> py> def prepostdecorator(pre, post, function):
> ... def wrapper(*args,**kwargs):
> ... pre()
> ... result = function(*args,**kwargs)
> ... post()
> ... return result
> ... return wrapper
> ...
> py> @partial(prepostdecorator, dopre, dopost)
> ... def sayhello(name):
> ... print "Hey %s, nice to meet you" % name
> ...
> py> sayhello('Tom')
> call pre
> Hey Tom, nice to meet you
> call post
>
> (3) Use a class:
>
> py> class prepostdecorator(object):
> ... def __init__(self, pre, post):
> ... self.pre, self.post = pre, post
> ... def __call__(self, function):
> ... def wrapper(*args,**kwargs):
> ... self.pre()
> ... result = self.function(*args,**kwargs)
> ... self.post()
> ... return result
> ... return wrapper
> py> @prepostdecorator(dopre, dopost)
> ... def sayhello(name):
> ... print "Hey %s, nice to meet you" % name
> ...
> py> sayhello('Tom')
> call pre
> Hey Tom, nice to meet you
> call post
>
> Note that in all of the above cases, the result of evaluating the
> expression after the @ is a callable object that takes _exactly one_
> argument, the function to be decorated.
>
> HTH,
>
> STeVe
>
> [1] http://www.python.org/peps/pep-0309.html
> --
> http://mail.python.org/mailman/listinfo/python-list
>
Wow thanks for the explanation!! Some of it is a bit mind bending to
me at the moment , but I'm going to mess with it a bit.
--
Thomas G. Willis
http://paperbackmusic.net
--
http://mail.python.org/mailman/listinfo/python-list
