On Tue, 2008-05-13 at 11:09 -0400, "Simón A. Ruiz" wrote: > kinuthia muchane wrote: > > On Mon, 2008-05-12 at 14:08 -0400, "Simón A. Ruiz" wrote: > >> For each of those numbers, it checks to see if any number between 2 and > >> i is divisible into i. If it finds anything, we know it's not a prime, > >> and so it breaks out of that second loop without completing it, which > >> means the else block isn't executed. > > > > This is where I am getting lost. When the variable 'number' is 3, it > > means that in that instance the inner 'for' statement will be 'for j in > > range(2,3)', hmmm which means that we will be dividing each element by 2 > > in the first 'for' statement and checking whether it is true , no? But > > 2%2 is zero, so, in my warped logic, the inner 'for' loop should break > > and the else clause will not execute! > > When i is 3, then we'll only check (2 % 3 == 0) which is False, so the > loop ends unbroken and runs the else clause letting us know that 3 is > indeed a prime number. Shouldn't we be checking for (3%2 == 0) instead of (2%3 == 0)? > > Never will we check (2 % 2 == 0). > > When i is 2, range(2,2) returns [], so the loop ends unbroken (without > starting) and runs the else clause. > > >> If it can't find anything that i is divisible by, then that inside for > >> loop finishes without breaking, we know that i is a prime number, and > >> the "else" clause is executed. > > > > This is where it gets even more interesting for me. Wont 'i' in one > > instance be 8, so at that particular moment there will be a 7 in the > > inner 'for' loop which will be divisible by one of our 'prime' numbers > > ie 7?! I know I am wrong but for some reason I cannot see the light! :-) > > Don't worry about it, you're doing fine. > > Remember, when you're most confused you're most ready to learn > something. :-D > > Ok, so when i is 8, we check: > is (8 % 2 == 0)? True. Break! > So, we've broken out of the inner loop and thus ignore the else > statement. We know 8 is not a prime number. > > Now, for a prime. When i is 7, we check: > is (7 % 2 == 0)? False. Next! > is (7 % 3 == 0)? False. Next! > is (7 % 4 == 0)? False. Next! > is (7 % 5 == 0)? False. Next! > is (7 % 6 == 0)? False. Next! > So, we've finished the inner loop without breaking, so we now run the > else clause: > is a prime number 7 > > > Does this help at all?
It was crystal clear! Thanks Simon (I didn't know how to put the accent mark over the 'o', though), the confusion is gone. ;) > > Hope this finds you all having a beautiful day! > > Simón _______________________________________________ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
