On Wed, Apr 16, 2014 at 10:09 AM, Yury Selivanov
There is a very common pattern for creating optional arguments when you can't use None:
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=
What if we add a standard marker for this use-case: functools.optional or inspect.Parameter.optional?
There is already a singleton which works very well for this use case: def foo(*, arg1='spam', arg3=None, arg4=NotImplemented): if arg4 is NotImplemented: # caller didn't pass *anything* for arg4 else: # caller did pass some (maybe None) value for arg4 It is already defined, and reads like sensible English.