On Jul 2, 10:41 am, Stephen Hansen <me+list/pyt...@ixokai.io> wrote:
> Okay, so!
>
> I actually never quite got around to learning to do deep and useful
> magic with decorators. I've only ever done the most basic things with
> them. Its all been a little fuzzy in my head: things like what order
> decorators end up being called in if there's more then one, etc.
>
> But in my current situation, what I'm wanting to do is have a decorator
> that wraps a function but which takes an *optional* argument, and sets
> that argument as an attribute on said function if its there.
>
> Here's what some tweaking and playing around has gotten me, as a recipe:
>
> import functools
>
> def my_decorator(arg):
> if callable(arg): # Stuck on 2.5. Leavemealone. :)
> protocol = None
> else:
> protocol = arg
>
> def wrap(fn):
> print "Wrapping."
> fn.protocol = protocol
>
> �...@functools.wraps(fn)
> def wrapper(*args, **kwargs):
> print "Calling."
> result = fn(*args, **kwargs)
> print "Called."
> return result
>
> return wrapper
>
> if not protocol: # argument-less decorator
> print "Calling wrap."
> return wrap(arg)
> else:
> print "Returning wrap."
> return wrap
>
> To be used as:
>
> class Thing(object):
> �...@expose
> def test1(self, arg1):
> return arg1
>
> �...@expose("testing")
> def test2(self, arg2):
> return arg2
>
> So, my question: am I doing this right? :) Some play-through testing
> appears to work. But, the dizzying array of nested def's up there leaves
> me a bit dazed, so I'm wondering if there's a simpler way to accomplish
> what I'm trying to do.
I usually recommend to factoring out magic parts into their own little
function, which then invoke the non-magical part in different ways:
def expose_as(protocol):
def wrap(fn):
print "Wrapping."
fn.protocol = protocol
@functools.wraps(fn)
def wrapper(*args, **kwargs):
print "Calling."
result = fn(*args, **kwargs)
print "Called."
return result
return wrapper
return wrap
def expose(arg):
"""Magic function to allow omitting argument."""
if type(arg) is types.FunctionType:
print "Calling with arg as function"
return expose_as(None)(arg)
print "Calling with arg as protocol"
return expose_as(arg)
I believe it's a good practice to isolate magic so that it's easy to
see, and also to ensure there's a non-magical way to do it if that is
needed. However, the world won't come to an end if you do it your
way.
Carl Banks
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