[Python-ideas] optional parameters

[Yury Selivanov]

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