On Mon, Jul 23, 2018 at 12:15:14PM +0100, Paul Moore wrote: > The examples are interesting, agreed. One thing they highlight to me > is that most uses of None are effectively convention. The only two > behaviours that are unique to None and implemented in the interpreter > are: > > 1. Functions that don't return an explicit value return None.
That is built into the language. > 2. The interactive interpreter does not display the value of a typed > expression when that value is None. But that is not built-in, it is merely the default behaviour. It is controlled by sys.displayhook, which can be customized: https://docs.python.org/3/library/sys.html#sys.displayhook We can have many interactive interpreters, including iPython, bpython, IDLE, etc and they don't necessarily suppress the printing of None. > One of the key points about this proposal That would be the None-aware PEP, not Jonathon's proposal to add documentation about None. > is that it adds a number of > additional ways in which the interpreter treats None specially (i.e., > four dedicated operators). That elevates None from the position of > being a commonly used sentinel value to one that has language support > for being a sentinel. None is already a special value. It is so special, it is one of only three built-in values given keyword status. All the other built-ins, including such things that are used implicitly by the interpreter (such as NotImplemented) are merely ordinary names. > That's not necessarily a bad thing, but it is a > point that should be considered when reviewing this PEP (people who > prefer to use object() for their sentinels are probably less happy > about making None "special", You make it sound like its a mere aesthetic choice. None is the default, recommended, most convenient sentinel. I use object() as a sentinel, when None is an otherwise ordinary value. I am also happy for None to be special, because it *is* special. -- Steve _______________________________________________ Python-ideas mailing list Python-ideas@python.org https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/
