> > > > This is inconsistent (and documented ;-).
But is it documented someplace easy for Sage users to find? Thanks! > For the operations "or" and > "and" Python actually uses "__nonzero__". *Not* "__or__" and "__and__" > which are the bitwise operation "|" and "&". > > They work as follows: > > In "x and y" if "x.__nonzero__()" is False then the result is "x" > otherwise it is "y". > > In "x or y" if "x.__nonzero__()" is True then the result is "x" and > otherwise it is "y". > > Examples: > > sage: 5 and 4 and 19 > 19 > sage: 4 and 0 and 12 > 0 > sage: 0 or 7 > 7 > > Similarly, even if X and Y are not defined you can write > > sage: False and X and Y > False > > The only way to fix Unknown would be to patch (non trivially) Python. > Boolean inherits from int... and it would be hard to have a third party > "Unknown" coherent with this inheritance. There was a slightly related > proposal, PEP 335, which was rejected with good reasons. We could > propose a new PEP for trooleans but it is not clear what should be the > concrete implementation. > > Vincent > > On 25/11/15 01:56, kcrisman wrote: > > On social media: > > > > sage: False or Unknown > > Unknown > > sage: Unknown or False > > False > > sage: False and Unknown > > False > > sage: Unknown and False > > Unknown > > > > It does seems somewhat inconsistent... > > > -- You received this message because you are subscribed to the Google Groups "sage-support" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-support+unsubscr...@googlegroups.com. To post to this group, send email to sage-support@googlegroups.com. Visit this group at http://groups.google.com/group/sage-support. For more options, visit https://groups.google.com/d/optout.
