On Fri, 05 Sep 2014 12:48:56 -0400, Seymore4Head <Seymore4Head@Hotmail.invalid> wrote:
>I'm still doing practice problems. I haven't heard from the library >on any of the books I have requested. > >http://www.practicepython.org/exercise/2014/04/16/11-check-primality-functions.html > >This is not a hard problem, but it got me to thinking a little. A >prime number will divide by one and itself. When setting up this >loop, if I start at 2 instead of 1, that automatically excludes one of >the factors. Then, by default, Python goes "to" the chosen count and >not "through" the count, so just the syntax causes Python to rule out >the other factor (the number itself). > >So this works: >while True: > a=random.randrange(1,8) > print (a) > for x in range(2,a): > if a%x==0: > print ("Number is not prime") > break > wait = input (" "*40 + "Wait") > >But, what this instructions want printed is "This is a prime number" >So how to I use this code logic NOT print (not prime) and have the >logic print "This number is prime" I am sure this has already been done, but after it was pointed out that you don't need to test for any number that multiplies by 2 it made me think again. If you start with the list [3,5,7] and step through the list of all remaining odd numbers (step 2), and start appending numbers that won't divide by numbers already appended in the list, that would seem like a pretty efficient way to find all prime numbers. -- https://mail.python.org/mailman/listinfo/python-list
