Path: csiph.com!fu-berlin.de!uni-berlin.de!not-for-mail
From: Chris Angelico <rosuav@gmail.com>
Newsgroups: comp.lang.python
Subject: Re: Late-binding of function defaults (was Re: What is a function parameter =[] for?)
Date: Sat, 21 Nov 2015 19:46:17 +1100
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On Sat, Nov 21, 2015 at 7:38 PM, Todd <toddrjen@gmail.com> wrote:
> Rather than a dedicated syntax, might this be something that could be
> handled by a built-in decorator?
>
> Maybe something like:
>
> @late_binding
> def myfunc(x, y=[]):

No, it can't; by the time the decorator runs, the expression has
already been evaluated. Without syntax, this can only be done with
gross hacks like lambda functions.

It could be done thus:

@late_binding
def myfunc(x, y=lambda: []):

and then the decorator could wrap the function. I'm not entirely sure
I could implement it reliably, but even leaving that aside, having to
put "lambda:" in front of everything is pretty ugly.

ChrisA