Gregory Morton wrote: > I'm having a problem understanding how this code works in lesson 4.4 on > the python tutorial. Can anyone explain it in easy-to-digest details? I > kind of know what most of the stuff means, but I can't comprehend how it > all works in unison. That, and I'm having a hard time understanding what > break does.
break exits the for loop immediately even if there is still items that need to be looped. The prime finding program's algorithm is by trial division; it tests whether the number is divisible from 2 to the number itself - 1 (since a prime number is defined as only divisible by 1 and the number itself). The for-loop's else suite is executed iff the loop exits normally (i.e. when range(2, n) is exhausted, i.e. not because of break). > > for n in range(2, 10): > .... for x in range(2, n): > .... if n % x == 0: > .... print(n, 'equals', x, '*', n//x) > .... break > .... else: > .... # loop fell through without finding a factor > .... print(n, 'is a prime number') > .... > 2 is a prime number > 3 is a prime number > 4 equals 2 * 2 > 5 is a prime number > 6 equals 2 * 3 > 7 is a prime number > 8 equals 2 * 4 > 9 equals 3 * 3 > > Thanks for all your help, > Greg > > > ------------------------------------------------------------------------ > > _______________________________________________ > Tutor maillist - Tutor@python.org > http://mail.python.org/mailman/listinfo/tutor _______________________________________________ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
