On Sun, May 24, 2020 at 01:38:26PM -0400, David Mertz wrote:
The pattern:
def fun(..., option=None): if option is None: option = something_else
Becomes second nature very quickly. Once you learn it, you know it. A line of two of code isn't a big deal.
Sure, but when you have seven parameters that all take late-bound defaults, it becomes a PITA. def func(...): # late binding boilerplate if dopey is None: if happy is None: if doc is None: if sneezy is None: if grumpy is None: if sleepy is None: if bashful is None: # AAAAND at last we get to the actual function body... This "if arg is None..." idiom is okay, but it's just a tiny bit of extra friction when coding. Nothing as drastic as a "design flaw" or a "wart" on the language, but it's slightly rough edge.
But this discussion DOES remind me of something much more general that I've wanted for a long time, and that has had long discussion threads at various times. A general `deferred` or `delayed` (or other spellign) construct for language-wide delayed computation would be cool. It would also require rethinking a whole lot of corners. I think it would address this mutable default, but it would also do a thousand other useful things.
Well, I don't know about a thousand, but I'm currently writing up a proto-PEP for delayed evaluation, and I've got six use-cases so far. -- Steven