[Python-ideas] Specifying constants for functions

[Bruce Leban]

On Tue, Oct 27, 2015 at 11:18 AM, Guido van Rossum <guido at python.org> wrote:

> IIRC it's an old micro-optimization; this was a common idiom at Zope. But
> I think it's way overused -- people believe it works so they do it all the
> time, even for code that's not performance sensitive, just because it's
> become a habit. (Like "register" in C in the '80s.)
>
> On Tue, Oct 27, 2015 at 10:55 AM, Yury Selivanov <yselivanov.ml at gmail.com>
> wrote:
>
>> Serhiy,
>>
>> On 2015-10-27 1:45 PM, Serhiy Storchaka wrote:
>>
>>> There is known trick to optimize a function:
>>>
>>>     def foo(x, y=0, len=len, pack=struct.pack, maxsize=1<<BPF):
>>>         ...
>>
>>
It's not a micro-optimization in this case:

def foo(x, SENTINEL=object()):
    ...


I don't like mangling function signatures to do this. What I really want is
the equivalent of C's static here:

def foo(x):
    static SENTINEL = object()
    ...


This has two important semantics: (1) the scope of the SENTINEL variable is
limited to the function foo; (2) it is only initialized once.

Hosting the value out of the function into a decorator like @asconstants is
fine.

--- Bruce
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