1 00:00:04,500 --> 00:00:08,890 Sometimes we need to check more than just two cases. So looking at the code 2 00:00:08,890 --> 00:00:14,420 from the last video, we're testing to see if age is greater than equal to 18 on line 5, 3 00:00:14,420 --> 00:00:19,780 and we test the opposite condition, age less than 18, on line 11. 4 00:00:19,820 --> 00:00:24,420 In both cases, the condition can be either True or False. If it's True, 5 00:00:24,420 --> 00:00:31,520 the code blocks on lines 6 and 7 and line 12 are executed. If the condition evaluates to False, 6 00:00:31,520 --> 00:00:36,480 the code in the else block executes. Python lets us test several conditions 7 00:00:36,480 --> 00:00:41,340 by using elif, so I'll explain a couple of rules about elif in a moment. 8 00:00:41,340 --> 00:00:45,640 Firstly though, let's see an example of using it. What I'm going to do is add another condition 9 00:00:45,640 --> 00:00:52,180 to the second if statement. So I'm gonna come down here to line 12, after line 12, 10 00:00:52,180 --> 00:00:59,160 you could do a backspace there. I'm going to type elif space age is equal to, that's two 11 00:00:59,160 --> 00:01:05,640 equal signs 900: and on the indented line I'm gonna type print, 12 00:01:05,640 --> 00:01:16,880 in parentheses double quotes, Sorry, Yoda you die in Return of the Jedi, 13 00:01:16,880 --> 00:01:23,840 and I've left the final else on line 15. So elif, if you haven't guessed it, is short for else if. 14 00:01:23,860 --> 00:01:28,520 The code now checks to see if age is less than 18. If it is, the message on 15 00:01:28,539 --> 00:01:33,399 line 12 will be printed. If age isn't less than 18, Python checks the elif 16 00:01:33,400 --> 00:01:40,020 condition on line 13. So that'll evaluate to either True or False. If True, 17 00:01:40,020 --> 00:01:43,660 we let Yoda know of his demise. We're assuming that anyone who's 900 years old must 18 00:01:43,660 --> 00:01:48,620 be Yoda from Star Wars, and if I just spoiled that movie for you I do apologize. 19 00:01:48,620 --> 00:01:51,640 But moving on, if the age doesn't equal 900, 20 00:01:51,640 --> 00:01:58,100 the condition evaluates to False and Python continues with the else on line 15. 21 00:01:58,100 --> 00:02:01,740 Now before I run the program, what I'm going to do is comment out the first if 22 00:02:01,749 --> 00:02:05,380 statement on lines 5 through 9, and instead of having to manually go through 23 00:02:05,380 --> 00:02:09,490 each line, most IDEs do have a quick way of doing that. So in IntelliJ I can just 24 00:02:09,490 --> 00:02:13,460 select the lines I want to comment out. I'm on Windows, I can do a control 25 00:02:13,460 --> 00:02:18,680 forward slash, and it's a Cmd / if you're on a Mac 26 00:02:18,680 --> 00:02:23,500 and the Ctrl slash will also work on Linux. Alright, so that's commented out 27 00:02:23,500 --> 00:02:28,620 and now won't execute. Let's run the program, and first, I'm going to enter Tim 28 00:02:28,629 --> 00:02:34,200 as my name again, which I've been doing. Then next we have to enter an age. 29 00:02:34,200 --> 00:02:39,000 We've got a few tests to perform, starting with the value less than 18, so let's try that 30 00:02:39,000 --> 00:02:44,540 and I'll do 11, and I'll just put the code on screen there, so we can see that. 31 00:02:44,540 --> 00:02:49,500 So you can see that's less than 18 that I entered, 11, and the code on line 12 was executed, 32 00:02:49,500 --> 00:02:52,340 and we got that output, and that's because the condition on line 11 33 00:02:52,359 --> 00:02:56,319 evaluated to a true, and just to be consistent let's check what happens when 34 00:02:56,320 --> 00:03:04,200 I enter an age of exactly 18. Tim and 18, 18 You're old enough to vote. 35 00:03:04,200 --> 00:03:08,100 Please put an X in the box, and this time the condition on line 11 36 00:03:08,100 --> 00:03:14,500 evaluated to False. Python then checks the elif condition, the else if, on line 13. 37 00:03:14,500 --> 00:03:18,960 This also evaluates to False and therefore, line 14 didn't get executed. 38 00:03:18,960 --> 00:03:23,040 Instead Python skipped to the else block. There's no more conditions to check and 39 00:03:23,080 --> 00:03:26,720 none of the ones that were checked were True, so we're left with the else. 40 00:03:26,720 --> 00:03:31,140 Lines 16 and 17 were executed and we get that message that You're old enough to vote, 41 00:03:31,140 --> 00:03:35,280 and to put an X in the box. And just to confirm, if we run this again, 42 00:03:35,280 --> 00:03:41,660 if I enter an age that's greater than 18, you should see the same result. So I put, say 45. 43 00:03:41,660 --> 00:03:46,080 Same result as we just talked about, when I entered 18. 44 00:03:46,080 --> 00:03:54,480 Alright, so the final test now is to enter 900 to see whether that works, and you can see there 900, 45 00:03:54,489 --> 00:03:58,449 Sorry Yoda you die in Return of the Jedi. So we're getting that message and 46 00:03:58,449 --> 00:04:03,760 that's because the elif, else if, for age is equal to 900, evaluates to True, 47 00:04:03,760 --> 00:04:08,079 and line 14 was executed. So all that would be much easier to understand if we could 48 00:04:08,080 --> 00:04:13,240 see the computer executing the code, line by line. Well as it happens we can do that. 49 00:04:13,240 --> 00:04:15,980 In the next couple of videos we're going to have a look at the debugger 50 00:04:15,980 --> 00:04:20,228 that's built into the IntelliJ IDEs. We're going to look at the IntelliJ and 51 00:04:20,228 --> 00:04:24,969 PyCharm debugger in the next video. In the video after that we'll see how to do 52 00:04:24,969 --> 00:04:28,029 the same thing with the debugger that's built into IDLE. Now if you're using 53 00:04:28,029 --> 00:04:31,340 a different IDE, it probably has a debugger as well, 54 00:04:31,340 --> 00:04:35,520 but please don't ask us how to use it. There's literally hundreds of IDEs, 55 00:04:35,520 --> 00:04:38,960 and we've chosen to use the Jetbrains products for this course. 56 00:04:38,960 --> 00:04:42,220 If you use something else, then that's either because you know how to use it, 57 00:04:42,220 --> 00:04:45,340 or there's someone in your company who does know. We can't, unfortunately, provide 58 00:04:45,340 --> 00:04:48,640 support for other IDEs, but if it's IntelliJ support you're after, were quite 59 00:04:48,640 --> 00:04:50,820 happy to help you with that. So let's move on now, 60 00:04:50,820 --> 00:04:54,140 and I'll see you in the next video.