Conditional decoration

[Devin Jeanpierre]

On Mon, Jun 18, 2012 at 6:49 PM, Emile van Sebille <emile at fenx.com> wrote:
> On 6/18/2012 3:16 PM Roy Smith said...
> class myDecorator(object):
>    def __init__(self, f):
>        self.f = f
>    def __call__(self):
>        print "Entering", self.f.__name__
>        self.f()
>        print "Exited", self.f.__name__

I dunno about other people, but I generally avoid class decorators
because they do not behave the way functions do when applied as a
decorator for a method.

This is a decorator taken out of some of my own source code. I was
mostly dicking around with things, as opposed to actually coding. The
docstring was even more ridiculous.

    from functools import reduce

    def rapply(*args):
        """apply(f, ...) <-> rapply(..., f)"""
        return args[-1](*args[:-1])

    def condecorator(condition, *decorators):
        if condition:
            return lambda f: reduce(rapply, reversed(decorators), f)
        else:
            return lambda f: f

Example usage:

    @condecorator(condition,
       decorator1,
       decorator2)
    def decorated(...):
        ...

equivalent to:

    def decorated(...):
        ...

    if condition:
        decorated = decorator1(decorator2(decorated))

-- Devin