On 03/12/2021 22:38, Chris Angelico wrote:
On Sat, Dec 4, 2021 at 8:18 AM Rob Cliffe via Python-ideas <python-ideas@python.org> wrote:
On 03/12/2021 19:32, Adam Johnson wrote:
The first unwelcome surprise was:
>>> def func(a=>[]): ... return a ...
>>> import inspect >>> inspect.signature(func).parameters['a'].default Ellipsis
Here the current behaviour of returning `Ellipsis` is very unfortunate, and I think could lead to a lot of head scratching — people wondering why they are getting ellipses in their code, seemingly from nowhere. Sure, it can be noted in the official documentation that `Ellipsis` is used as the indicator of late bound defaults, but third-party resources which aim to explain the uses of `Ellipsis` would (with their current content) leave someone clueless.
+1. This may be a very naive question, apologies if it's nonsense. Instead of Ellipsis, would it be possible to have a built-in LateBound class and use instances of that class instead of Ellipsis? The __str__ method of the inspect.Parameter class could be modified to return something like "a=>[]" (or whatever syntax is adopted for specifying late-bound defaults) in such cases. The __repr__ and __str__ methods of a LateBound object could return something like, respectively, "LateBound('[]')" "[]" I am sure there is code that uses inspect.signature that would be broken, but isn't that inevitable anyway?
That's a possibility for the inspect module. For the core language - and therefore for anything that directly inspects the function's dunders - it's much more efficient to use a well-known object. OK. I'm guessing that by "well-known" you mean pre-existing. Python has a number of built-in singleton objects (None, True, False, Ellipsis). What about adding a new one called LateBound (or other bikeshed colour)? Best wishes Rob Cliffe In the current implementation, I've kept inspect.signature() consistent with the dunders, but if there's good reason to change, I wouldn't be averse to it. But I would need feedback from people who make heavy use of inspect.signature, as I don't do much with it other than the basics of help().
Everything in the reference implementation that isn't part of the PEP should be considered provisional at best :)
ChrisA _______________________________________________ Python-ideas mailing list -- python-ideas@python.org To unsubscribe send an email to python-ideas-leave@python.org https://mail.python.org/mailman3/lists/python-ideas.python.org/ Message archived at https://mail.python.org/archives/list/python-ideas@python.org/message/B3NBYK... Code of Conduct: http://python.org/psf/codeofconduct/