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Wed Feb 25 16:21:02 EST 2004 · https://mail.python.org/pipermail/python-dev/2004-February/042720.html

On Feb 25, 2004, at 4:02 PM, Skip Montanaro wrote:

>
>     Michael>   The "def name [modifiers]:" is unpythonic because:
>     Michael>    * It re-uses the "[]" for a completely new purpose, 
> unrelated
>     Michael>      to lists or indexing.
>
> Not necessarily.  It names a list of functions to be applied to this
> function to get the final definition (I'll leave it to others to 
> figure out
> the order of application :-).  In particular, you could probably dream 
> up
> some rather "interesting" list constructors which would allow the 
> programmer
> (or even the user) to modify the behavior at function definition time:
>
>     def is_enabled(m, fname, tracers=os.environ.get("TRACERS", "")):
>         "ex: TRACERS=func1:trace,func2:count_lines ; export TRACERS"
>         return tracers.find("%s:%s"%(fname,m.__name__)) != -1
>
>     modifiers = [trace, profile, count_lines]
>
>     def func1(a,b,c) [m for m in modifiers if is_enabled(m, "func1")]:
>         ...
>
>     def func2(a,b,c) [m for m in modifiers if is_enabled(m, "func2")]:
>         ...
>
> that it would necessarily be good to always use such 
> complex
> constructs, but it might provide some as-yet-unanticipated power for
> debugging or other magic.  If you are going to add [...] as a function
> modifier syntax, I would argue that it should allow the full power of 
> list
> (or generator) comprehensions.

I agree with you here, but the patch doesn't do that yet.  Right now 
you would need to do something like:

def fnseq(lst):
     def fnseq(fn):
         for obj in lst:
             fn = obj(fn)
         return fn
     return fnseq

def func1(a,b,c) [fnseq([m for m in ...])]:

-bob

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[Python-Dev] Re: new syntax for wrapping (PEP 318)