On Fri, May 14, 2021 at 7:31 PM Petr Viktorin <encu...@gmail.com> wrote:
> Perhaps it would be beneficial to provide a common base class or
> factory, so we get a good repr. But I don't think another common value
> like None and Ellipsis would do much good.
>
Agreed - I think Sentinel would make a great class, from which you
instantiate purpose-specific sentinels.
But maybe there really needs to be a way to NOT specify an argument,
and to find out that an argument wasn't specified? Defaulting is only
one way to handle it. Consider:
def truly_optional_arg(x, y, *z):
"""Two mandatory args, and then an optional one"""
if z: print("Got an extra arg")
pass_arg = input("Pass the arg? ") == "y"
truly_optional_arg(10, 20, *([30] if pass_arg else []))
It's horrifically ugly, but it really and truly does/doesn't pass that
argument, and it really and truly detects whether one was passed. To
make that sort of thing actually viable, there'd need to be some sort
of language support; maybe something where the local name would start
out unbound, but testing for a local's boundness is a clunky
try/except, so that might also need some support.
Do we ever really need the ability to pass a specific sentinel to a
function, or are we actually looking for a way to say "and don't pass
this argument"?
ChrisA
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