[Python-ideas] optional parameters

[Guido van Rossum]

TBH I think it's usually an anti-pattern when you have an API where the
absence of a parameter is not equivalent to some default value. It makes
wrapping such APIs awkward, e.g.

def logging_foo(*, arg1='something_other_than_spam', arg3=None,
arg4=<what???>):
    loging.info('calling foo(arg1=%r, arg3=%r, arg4=%r)', arg1, arg3, arg4)
    return foo(arg1=arg1, arg3=arg3, arg4=arg4)


On Wed, Apr 16, 2014 at 10:09 AM, Yury Selivanov <yselivanov.ml at gmail.com>wrote:

> Hello,
>
> There is a very common pattern for creating optional arguments
> when you can't use None:
>
> _optional = object()
> def foo(*, arg1='spam', arg3=None, arg4=_optional):
>     if arg4 is _optional:
>         # caller didn't pass *anything* for arg4
>     else:
>         # caller did pass some (maybe None) value for arg4
>
> It's a bit annoying to create this marker objects, and also,
> if you try to render a signature of such function, you'll get
> something like:
>
> "(*, arg1='spam', arg3=None, arg4=<object object at 0x104be7080>)"
>
> What if we add a standard marker for this use-case:
> functools.optional or inspect.Parameter.optional?
>
>
> Yury
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-- 
--Guido van Rossum (python.org/~guido)
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