On Sun, May 24, 2020 at 12:55 PM Chris Angelico <ros...@gmail.com> wrote:
>
> And it isn't entirely correct, because now None isn't a valid
> parameter.
Which is indeed, an extremely common use case :-)
> It's an extremely common idiom right up until it doesn't
> work, and you need:
>
> _SENTINEL = object()
> def fun(..., option=_SENTINEL):
> if option is _SENTINEL:
> option = something_else
>
I've thought to a while that there should be a more "standard" way to so
this:
A NOT_SPECIFIED singleton in builtins would be pretty clear.
(though I'd like to find a shorter spelling for that)
BTW, though I do find it tedious to write the:
if option is SOME_SENTINEL:
option = something
...
It's not always the case that it's a simple setting of the value to a empty
mutable -- sometimes there's some more complexity there. Which is why I
kind of like that it's explicit. But if we did make it simpler, I like the
idea of providing a factory function, so it would be possible to do more
complex things than a simple empty container of some sort.
Though that factory wouldn't have access to the full function namespace, so
maybe not that flexible.
-CHB
--
Christopher Barker, PhD
Python Language Consulting
- Teaching
- Scientific Software Development
- Desktop GUI and Web Development
- wxPython, numpy, scipy, Cython
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