1 00:00:00,150 --> 00:00:04,320 Now the next tip has been the thing that you've probably been screaming out for. 2 00:00:05,010 --> 00:00:10,010 Why don't we use print? And indeed you are correct. 3 00:00:10,200 --> 00:00:14,220 Print is basically your best friend. Now as developers 4 00:00:14,250 --> 00:00:15,870 I know we don't have a lot of friends, 5 00:00:16,230 --> 00:00:20,220 but at least we can rely on print to be our trusty friend. 6 00:00:21,120 --> 00:00:25,650 Do you have heartbreak? Use print. Now print probably can't help you with your 7 00:00:25,650 --> 00:00:28,650 relationship issues or family issues, 8 00:00:28,920 --> 00:00:32,100 but it can help you debug your code, 9 00:00:32,430 --> 00:00:34,590 which is a pretty decent thing for it to do. 10 00:00:35,280 --> 00:00:40,280 So let's go ahead and comment out the previous block and let's uncomment this 11 00:00:40,920 --> 00:00:45,690 one. And now I'm sure you're pretty much dying to use print to solve these 12 00:00:45,690 --> 00:00:49,560 debugging issues. Why Angela? Why haven't you been using it before? Well, 13 00:00:49,560 --> 00:00:51,990 I've been saving it for this perfect moment. 14 00:00:52,710 --> 00:00:57,710 Take a look at the code and see if you can use print as your friend to help you 15 00:00:58,410 --> 00:01:02,070 solve the issue. Pause the video now and give that a go. 16 00:01:04,430 --> 00:01:05,630 So here, we've got 17 00:01:05,780 --> 00:01:10,780 a very simple program that figures out the number of words in a book. Pages 18 00:01:11,690 --> 00:01:14,960 starts out zero, words starts out at zero, 19 00:01:15,440 --> 00:01:20,440 and we have to input the number of pages in our book and the number of words in 20 00:01:20,450 --> 00:01:21,260 our book. 21 00:01:21,260 --> 00:01:26,260 And then we multiply the pages by the words to calculate the total number of 22 00:01:26,330 --> 00:01:30,350 words in the book and then we print it out. But if we have a go, 23 00:01:30,380 --> 00:01:32,990 you can see that let's say we have, um, 24 00:01:33,020 --> 00:01:38,020 45 pages making a booklet and we have 250 words per page and we get 0. 25 00:01:40,940 --> 00:01:44,900 So the output that's supposed to tell us the total number of words in the book 26 00:01:45,320 --> 00:01:47,990 ends up being 0. So what's going on here? 27 00:01:48,860 --> 00:01:53,330 How can we debug this? Let's go ahead and use print. 28 00:01:53,810 --> 00:01:55,820 What are our assumptions? Well, 29 00:01:55,880 --> 00:01:59,300 we're actually getting the number of pages and the number of words correct 30 00:01:59,330 --> 00:02:00,890 so that we can calculate this. 31 00:02:01,310 --> 00:02:05,720 Why don't we add some print statements before the final one? Let's print 32 00:02:05,750 --> 00:02:10,580 what's the actual value of some of our variables that we're getting from the 33 00:02:10,580 --> 00:02:14,030 user. For example, I could say, um, 34 00:02:15,200 --> 00:02:20,200 the pages equals and then insert the pages variable in here in an fstring. 35 00:02:22,730 --> 00:02:27,560 And I can also print my other variable in an fstring, 36 00:02:27,680 --> 00:02:31,400 which is the word per page variable. 37 00:02:31,910 --> 00:02:36,910 And this is equal to let's insert that variable as well. 38 00:02:37,850 --> 00:02:40,190 And now when I run my code, 39 00:02:40,220 --> 00:02:44,180 I've got my print statements going and I can test it out. 40 00:02:44,300 --> 00:02:49,300 So we still got 45 pages and then 250 words per page. 41 00:02:50,030 --> 00:02:54,680 Now you can see that my variables are logged. So this one, 42 00:02:54,680 --> 00:02:59,000 this pages variable does equal 45. So it captured my data correctly. 43 00:02:59,410 --> 00:03:02,080 But the word per page equals 0, 44 00:03:02,320 --> 00:03:06,400 which is not what I entered at all. I entered 250 45 00:03:06,490 --> 00:03:08,950 so I was expecting this to be 250. 46 00:03:10,120 --> 00:03:13,030 So now using print, my best friend, 47 00:03:13,450 --> 00:03:15,190 I've managed to narrow down the problem. 48 00:03:15,250 --> 00:03:17,590 It's something to do with this variable. 49 00:03:17,740 --> 00:03:21,220 So let's take a look at what's going on here. Well, 50 00:03:21,550 --> 00:03:23,200 I've spotted the problem, 51 00:03:23,290 --> 00:03:27,310 have you? Pause the video and see if you can fix this code 52 00:03:27,460 --> 00:03:31,840 so the final total number of words actually gets printed when you run the code. 53 00:03:32,440 --> 00:03:35,650 Pause the video now. All right, 54 00:03:35,680 --> 00:03:40,000 we've narrowed down to this one line of code that's probably broken. 55 00:03:40,900 --> 00:03:45,790 And if you look closely, you'll see that instead of a single equal sign 56 00:03:45,820 --> 00:03:47,350 which means assignment, 57 00:03:47,740 --> 00:03:51,160 this variable should be equal to this value. 58 00:03:51,820 --> 00:03:53,920 We had two equal signs. 59 00:03:54,370 --> 00:03:58,660 This means does this variable equal this value? 60 00:03:59,230 --> 00:04:03,820 And this actually gets evaluated and becomes either true or false. 61 00:04:04,330 --> 00:04:08,770 Now, in this case, it's actually false. Words per page starts out being equal to 62 00:04:08,770 --> 00:04:11,710 zero, and then it becomes equal to 250. 63 00:04:12,520 --> 00:04:17,110 So if this line of code is false, then that's just left as it is, 64 00:04:17,140 --> 00:04:18,880 it doesn't actually affect anything. 65 00:04:19,360 --> 00:04:24,190 And this total word is still using zero, which is why it's printing out zero. 66 00:04:24,790 --> 00:04:29,440 So now that we've identified the issue, all we have to do to fix it is that. 67 00:04:30,310 --> 00:04:31,870 And if we run our code again, 68 00:04:34,860 --> 00:04:37,770 you can see it works exactly as it should do.