Mathew Elman writes:
I believe this is a rebirth of a request that has come up many times before, which is to have something like javascript's `undefined` where it means "use the default value" if passed to a function that has a default value or "value not provided" (slightly different to "None"). [...] "undefined" would either have to be an alias for "None" everywhere _except_ function signatures, or be only allowed in function signatures and have special handling.
Either would be a significant complication in Python semantics, though. And I don't really see how the latter works: notdefined = None def foo(x=undefined): # here notdefined = x return wrapped_function(x) # there foo() print(notdefined) To get this "use the default" functionality from #here to #there, either the above has to allow you to capture the object representing undefined but you're not allowed to use the name "undefined" for it (very un-Pythonic), or there has to be some horrifying magic, maybe macro-like, that turns the name "x" into a name that isn't there.
It opens up a can of worms in javascript but has its uses.
If you're phishing, I guess worms are useful. *shudder* Wisecracks aside, I'm not sure I want to read code designed so that 'undefined' is genuinely useful. I'd need to see real code that uses it, plus the translation to Python, plus some argument why it has to be that way, before I'd be willing to go higher than -1 on this complication.