On Wednesday, September 17, 2014 6:10:35 PM UTC+3, Chris Angelico wrote: > On Thu, Sep 18, 2014 at 12:55 AM, cool-RR <ram.rac...@gmail.com> wrote: > > Terry, that doesn't really answer the question "why", it just pushes it > > back to the documentation. Is there a real answer why? Why return NaN when > > Inf would make mathematical sense? > > > To answer that, we have to first look at what it means to do > operations on Inf. The definition of "Infinity + 1" is the limit of "x > + 1" as x goes toward positive infinity - which is positive infinity. > Same with infinity-1, infinity/1, infinity*1, etc, etc, etc. So far, > so good. But as x tends toward positive infinity, the value of "x // > 1" (or simply of floor(x)) doesn't simply increase tidily. It goes up > in little jumps, every time x reaches a new integer.
Despite the fact it goes up in jump, it still satisfies the mathematical condition needed for a limit. (I won't quote the epsilon-delta thing but I think you can find it.) > And while it's > conceivable to define that infinity divided by anything is infinity, > and infinity modulo anything is zero, that raises serious issues of > primality and such; > I'm not sure that that would really help anything. I didn't ask for the modulo, I agree it should remain NaN. I'm talking about the floor division. I don't see any problems this will cause with primality. "I'm not sure that that would really help anything" is a little bit too vague. Thanks, Ram. -- https://mail.python.org/mailman/listinfo/python-list
