I am a -0 on this, but I think it was Greg Ewing that presented a real use case:
There is no way to use literal_eval that gets you an inf (or NaN value). Which is a real, though maybe not important, use case. -CHB On Fri, Sep 4, 2020 at 7:15 PM Steven D'Aprano <st...@pearwood.info> wrote: > On Fri, Sep 04, 2020 at 09:40:55PM -0400, Cade Brown wrote: > > > The `eval(repr(x)) == x` is not a segment of my code; rather it is part > of > > > Python's description of what 'repr' should do: > > > > > > https://docs.python.org/3.4/library/functions.html?highlight=repr#repr > > > > > > > > > Specifically: ` For many types, this function makes an attempt to return > a > > > string that would yield an object with the same value when passed to > eval()` > > > <https://docs.python.org/3.4/library/functions.html?highlight=repr#eval> > > > > "For many types" and "makes an attempt". > > > > There has never been, and never will be, a guarantee that all objects > > will obey that invariant. As I said, it is a Nice To Have, and it is > > designed for convenience at the interactive interpreter. > > > > > > > So everyone in this thread can stop mentioning security concerns; I'm > sure > > > we're all aware of those and we should instead focus on what repr should > do > > > and shouldn't do. > > > > You specifically said that math.inf doesn't solve your problem *because* > > `eval(repr(x))` doesn't work. Now you are backpeddling and saying that > > this is not your actual problem. > > > > (In fact it does work, if you do it correctly.) > > > > There are a million other objects that don't obey that invariant: > > > > py> x = object() > > py> eval(repr(x)) == x > > SyntaxError: invalid syntax > > > > > > Why is float infinity so special that it needs to obey the > > invariant? > > > > What's the actual problem, or problems, in your code that you are trying > > to solve by making an infinity builtin? If there is no actual problem > > being solved, and the only reason you want this is because: > > > > > > > I think it's weird to not fulfill this promise > > > > > > you don't have any sympathy from me: > > > > - `eval(repr(x))` is not a promise, it is a mere suggestion > > that *some* types *try* to provide. > > > > - Adding a special built-in constant Infinity just to satisfy > > this Nice To Have feature is overkill. > > > > - It would require float infinities to change their repr from > > 'inf' to 'Infinity', and that will break doctests. > > > > - And even if that feature were satisfied by infinity, it > > couldn't be satisfied by float NANs by their very definition: > > > > py> from math import nan > > py> nan == nan > > False > > > > So while the cost of adding a new Infinity builtin is small, the benefit > > is even smaller. > > > > > > -- > > Steve > > _______________________________________________ > > Python-ideas mailing list -- python-ideas@python.org > > To unsubscribe send an email to python-ideas-le...@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/AHJETD7PM6M6IKERP7NYNGYWAJBZDS27/ > > Code of Conduct: http://python.org/psf/codeofconduct/ > > -- Christopher Barker, PhD Python Language Consulting - Teaching - Scientific Software Development - Desktop GUI and Web Development - wxPython, numpy, scipy, Cython
_______________________________________________ Python-ideas mailing list -- python-ideas@python.org To unsubscribe send an email to python-ideas-le...@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/QIGOPPNQS3PJUHB3RFJ3FXAJWPVVDWDF/ Code of Conduct: http://python.org/psf/codeofconduct/
