On Tue, Oct 25, 2011 at 12:50 PM, Joachim Durchholz <[email protected]> wrote: > Am 25.10.2011 18:33, schrieb Aaron Meurer: >>> >>> The issue report suggests testing for non-"intness" via >>>>>> >>>>>> int(N) != N >>>>>> What's the best way to test for "floatness" in Python? >>>>>> >>>>> >>>>> This is not what the issue suggests. >>>>> >>>> >>> Why is this important? >>> More specifically, I do not fully understand why extending the issue to >>> cover more functions is okay, but extending the domain of parameter >>> values >>> is not. >>> Might be some ramifications that I don't know yet - in which case I'd >>> like >>> to know :-) >>> >> >> I'm afraid I don't understand what you're asking here. If you're asking >> why >> you can't use floats, you can. Calling int() on a float will truncate it, >> but it doesn't matter, because it's just a range over the integers. >> Actually, I guess you would really need to call ceil() in that case. >> >> Did I understand your question correctly? > > That's answers I already had, so, I fear that's not the case :-) > > I see that the functions in generate.py fall into two classes: > > 1. Those that identify primes by index. I.e. you ask for the tenth prime and > get 23. > For these, calling int() would be just fine; asking for the 2.5th prime > would not make much sense after all. > > 2. Those that identify primes by magnitude. I.e. you ask for the list of > primes between 20 and 30 and get [23, 29]. > For these, I'm suggesting to use float(), so we can ask for the list of > primes between 19.5 and 30.5. In fact, primerange(19.5, 30.5) would do > exactly that, which is what got me thinking in that direction in the first > place :-) > > Aaahh... I wasn't aware that int(some_float) simply truncates some_float to > its integer part, which would be as useful for searching in the primes array > as a float (and maybe be a bit faster). > Now I'm wondering why primerange(a, b) uses float()... > > Regards, > Jo
So actually, using float() is probably cleaner than using int() as I had previously suggested, because to really do it correctly, you would actually have to use floor() and ceil(). So go ahead and just use that. There really isn't much concern with it since you are just comparing it (maybe someone can correct me if I am wrong). Aaron Meurer > > -- > You received this message because you are subscribed to the Google Groups > "sympy" group. > To post to this group, send email to [email protected]. > To unsubscribe from this group, send email to > [email protected]. > For more options, visit this group at > http://groups.google.com/group/sympy?hl=en. > > -- You received this message because you are subscribed to the Google Groups "sympy" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/sympy?hl=en.
