[Python-ideas] PEP-3150

[Carl M. Johnson]

On Wed, Apr 13, 2011 at 10:06 PM, Greg Ewing
<greg.ewing at canterbury.ac.nz> wrote:

> In this particular case (i.e. a function that does nothing
> but define and return another function) I'd like to be able
> to write
>
>  def decorator(f)(*args, **kwargs):
>    do something...
>
> but that's a subject for another hotly-debated PEP!

Interesting, but could that be extended to support making a throwaway
key function for sorted? With given it's obviously

sorted_list = sorted(original_list, key=keyfunc) given:
   def keyfunc(item):
       item = item.replace(" ", "")
       item = item.lowercase()
       ...
       return item

but I can't see how that your proposal could be expanded beyond the
one use case of decorator making, and today it's already possible to
make a simple decorator decorator that injects f as the first arg:

class MetaDec:
   def __init__(self, dec):
       self.dec = dec

   def __call__(self, f):
       def callme(*args, **kwargs):
            return self.dec(f, *args, **kwargs)
       return callme

@MetaDec
def logger(f, *args, **kwargs):
   print("Logging...")
   return f(*args, **kwargs)

@logger
def foo():
   print("Foo!")

I think the recipe for something like this is already in the docs
somewhere... Obviously, a built-in syntax for simple decorators might
have some savings in efficiency, but I would be surprised if it were
especially noteworthy, since decoration typically happens many fewer
times than function invocation.

Hmm, as I look at the given syntax here again, I find that I don't mind
the extra level of indention. Also, you can add another docstring to
clarify things a bit:


sorted_list = sorted(original_list, key=keyfunc) given:
   "A list of widgets sorted by removing whitespace and lowercasing..."
   def keyfunc(item):
       ...

>>> help(sorted_list)
"A list of widgets sorted by removing whitespace and lowercasing..."