1 00:00:04,720 --> 00:00:09,910 In the last video, we saw how a binary chop can be used, to reduce the number of 2 00:00:09,910 --> 00:00:15,160 guesses needed. In this video, we'll write the code to let the computer guess a number. 3 00:00:15,160 --> 00:00:17,240 The code will implement the algorithm 4 00:00:17,240 --> 00:00:22,240 that we discussed in the slides, in the last video. So an algorithm is a set of 5 00:00:22,240 --> 00:00:27,820 steps that are followed, to perform a task or calculate a result. So I'm going 6 00:00:27,820 --> 00:00:31,539 to start with a couple of variables for our low and high values. We need a new 7 00:00:31,540 --> 00:00:41,440 file for this, and we're going to call this new Python file hilo. 8 00:00:41,440 --> 00:00:49,200 We're gonna take the opportunity to close some of these other tabs. Alright, so the variables I'm 9 00:00:49,210 --> 00:00:55,750 starting with: low equals one and high equals 1000. So next we need some simple 10 00:00:55,750 --> 00:01:00,340 instructions and get the program to wait until we're ready. So on line 3, print 11 00:01:00,340 --> 00:01:12,120 parentheses double quotes Please think of a number between, 12 00:01:12,120 --> 00:01:16,520 and we need our left and right curly braces and another set of left and right curly braces, 13 00:01:16,520 --> 00:01:21,780 because obviously we're going to change that to the actual numbers, dot format outside of 14 00:01:21,780 --> 00:01:27,740 the double quotes, low comma high in parentheses and the closing parenthesis. 15 00:01:27,740 --> 00:01:33,300 Then we need to add a line to get started, so import parentheses double quotes, 16 00:01:33,300 --> 00:01:39,660 press ENTER to start. So on line 5, we're not interested in anything that 17 00:01:39,670 --> 00:01:43,479 the human types. We're just calling the input function so that the computer 18 00:01:43,479 --> 00:01:47,840 waits until the user presses the enter key to start the game. 19 00:01:47,840 --> 00:01:52,159 It will be useful to count the number of guesses. We know that the computer should 20 00:01:52,159 --> 00:01:56,690 be able to get the correct answer with ten guesses at most, and that's because 21 00:01:56,690 --> 00:02:03,000 we're having the range of numbers each time, and two to the power of 10 is 1,024. 22 00:02:03,000 --> 00:02:07,180 So that's slightly more than 1,000. In fact, the computer can guess any number 23 00:02:07,190 --> 00:02:13,550 from 1 to 1,023, within 10 guesses. But 1,023 is a strange number to 24 00:02:13,550 --> 00:02:18,200 show to the user. That's why we're sticking with 1,000. Alright so we need 25 00:02:18,200 --> 00:02:21,120 a variable now to store the number of guesses, 26 00:02:21,120 --> 00:02:26,360 so on line 7, I'll type guesses equals 1. Alright so we'll use a while loop to 27 00:02:26,360 --> 00:02:30,350 let the computer keep guessing until it gets the answer. After each guess the 28 00:02:30,350 --> 00:02:34,610 human will tell the computer whether to guess higher or lower, or if it got the 29 00:02:34,610 --> 00:02:38,959 answer right. We'll keep looping until the answer is correct and break out of 30 00:02:38,960 --> 00:02:46,180 the loop when it is. So I'm going to do a while True colon, then on line 9, 31 00:02:46,180 --> 00:02:55,800 guess equals low plus, and in parentheses, high take low, integer division so two slashes there, 2. 32 00:02:55,800 --> 00:02:58,459 So we're dividing by 2 there and making sure that we're using integer 33 00:02:58,460 --> 00:03:03,460 division. Now I mentioned while True in an earlier video. True is always true, 34 00:03:03,460 --> 00:03:05,920 which means this loop will go round forever. 35 00:03:05,920 --> 00:03:09,340 Sometimes it's easier to do that then break out of the loop at some point, 36 00:03:09,340 --> 00:03:12,720 rather than trying to include a condition in the while loop. So what we 37 00:03:12,739 --> 00:03:16,970 want, is for the loop to stop when the computer gets the right answer, but 38 00:03:16,970 --> 00:03:21,709 because the computer doesn't know the answer, we can't include a test here. So 39 00:03:21,709 --> 00:03:26,570 what I mean is, on line 8 here, we can't do something like wild guess is not 40 00:03:26,570 --> 00:03:31,549 equal to answer, because we don't actually know the value of answer. So I'm going to 41 00:03:31,549 --> 00:03:35,359 do that change and go back to what we had, while True, so that the program will 42 00:03:35,359 --> 00:03:39,769 keep looping. The line 9 is the formula that we saw in the slides in the 43 00:03:39,769 --> 00:03:44,359 previous video. It calculates the midpoint between the low and high values 44 00:03:44,359 --> 00:03:49,370 to produce the next guess. So what we'll do is we'll print the guess, then ask the 45 00:03:49,370 --> 00:03:53,480 user to type H if the computer should guess higher, L if the computer should guess 46 00:03:53,480 --> 00:03:58,489 slower or C if the guess was correct. And we can include the text that we want to 47 00:03:58,489 --> 00:04:02,840 print in the input prompt. So I'm going to come down here, line 10, 48 00:04:02,840 --> 00:04:12,640 high underscore low is equal to input parentheses double quotes My guess 49 00:04:12,640 --> 00:04:17,930 is and left and right curly braces. Full stop. Should I guess 50 00:04:17,930 --> 00:04:32,440 higher or lower? - should I type better as well. Should I guess higher or lower? Enter h 51 00:04:32,440 --> 00:04:40,820 or l, or c if my guess was correct, and then double quotes, and we can't really see 52 00:04:40,820 --> 00:04:44,580 now and I'm going to actually talk about having lines that are too long, in a minute. 53 00:04:44,580 --> 00:04:49,700 We're gonna keep typing for now and put dot format left parenthesis guess 54 00:04:49,700 --> 00:04:55,300 two right parentheses, then outside of that I'm going to do dot casefold. So again, as I 55 00:04:55,310 --> 00:04:59,030 pointed out there, that line is a bit long. So you can easily see here the 56 00:04:59,030 --> 00:05:01,820 problem that long lines can cause, because it's hard for me to show it all 57 00:05:01,820 --> 00:05:06,060 on the video. In fact, I can't show the entire line on the video right now. 58 00:05:06,060 --> 00:05:09,500 I don't want to digress here, but I will be talking about line length and other 59 00:05:09,500 --> 00:05:13,280 things about formatting a code in a later video. Remember this example and 60 00:05:13,280 --> 00:05:17,810 how inconvenient it is for you to type the code from my screen, when we come 61 00:05:17,810 --> 00:05:21,409 back to code style, noting that you can't see it all at once. For now, though, what I'm 62 00:05:21,409 --> 00:05:24,979 going to do is split this line. So I'm going to position the cursor before 63 00:05:24,980 --> 00:05:30,600 the E of enter. I'm going to type a double quote, then I'm going to press Enter. 64 00:05:30,600 --> 00:05:34,340 That gives an error, as you can see, but that's okay, just enter another double 65 00:05:34,340 --> 00:05:38,990 quote here and that then delimits the split-up string correctly. If I go back 66 00:05:38,990 --> 00:05:42,860 now, we can see the whole thing on the screen. The double quote should line up 67 00:05:42,860 --> 00:05:46,550 with the one on the line above but don't worry too much about that just yet. We'll 68 00:05:46,550 --> 00:05:49,699 leave it as it is for now. What we will do is position the cursor again before the 69 00:05:49,699 --> 00:05:55,849 dot of format, up here before the dot, press ENTER again. That's now split the 70 00:05:55,849 --> 00:05:59,840 line into three. Now rather than lining up manually, what you could do is go to 71 00:05:59,840 --> 00:06:07,060 the code menu and choose Reformat code. Most modern IDEs have a similar feature, 72 00:06:07,060 --> 00:06:11,000 and now the code is correctly formatted, as you can see. Alright so I think you'd 73 00:06:11,000 --> 00:06:14,810 agree now, that's easier to read. You can now see all the code on my screen and I 74 00:06:14,810 --> 00:06:17,240 don't have to scroll sideways as much to show it to you. 75 00:06:17,240 --> 00:06:20,680 Alright so moving on with this program, we've got four possibilities to deal 76 00:06:20,680 --> 00:06:26,840 with. The user could enter h for a high guess, so let's start with that. 77 00:06:26,840 --> 00:06:35,980 So I'll start that on line 14. If high underscore low is equal to 78 00:06:35,980 --> 00:06:40,100 h in lowercase : Remember we're using case fold on line 12, 79 00:06:40,100 --> 00:06:43,760 so we're guaranteed it's going to be in lowercase. And the comment here, we want 80 00:06:43,760 --> 00:06:56,680 to Guess higher. The low end of the range becomes 1 greater than the guess. 81 00:06:56,680 --> 00:06:59,680 Now I'm not going to add the code for guessing higher. Let's get all the 82 00:06:59,690 --> 00:07:03,440 conditions in place first. That'll let you see what the conditions are, but it 83 00:07:03,440 --> 00:07:06,950 will cause a problem. Because the error message is very confusing, I want to get 84 00:07:06,950 --> 00:07:12,020 the error and explain it. Right, so moving on now, the next condition to test is if 85 00:07:12,020 --> 00:07:16,920 the user enters l for lower. So we're going to go ahead and do that on line 17: 86 00:07:16,920 --> 00:07:23,540 elif high_low is equal to l : again in lower case, and a comment 87 00:07:23,540 --> 00:07:28,580 for that will be Guess lower. The high end of the range becomes 1 less than the guess. 88 00:07:34,000 --> 00:07:36,940 So we're getting errors here but we'll ignore them for the moment. 89 00:07:36,940 --> 00:07:40,460 Next the input would be c if the guess is correct, so let's move down on to that, 90 00:07:40,460 --> 00:07:47,780 line 20, elif high_low is equal to c in double quotes, lower case c : 91 00:07:47,780 --> 00:07:51,140 So what I'll do here is print out the answer here, no need to add a comment, so print 92 00:07:51,140 --> 00:07:56,720 parentheses double quotes I got it in, left and right curly braces 93 00:07:56,720 --> 00:08:03,950 guesses exclamation mark double quote dot format guesses. Alright we'll scroll up a 94 00:08:03,950 --> 00:08:07,670 little bit so we can see the other code. Alright so that's the three conditions 95 00:08:07,670 --> 00:08:11,690 that we expect, but humans often don't do what we expect, and we should also deal 96 00:08:11,690 --> 00:08:15,700 with anything else that they might type. We're gonna use an else block to do that. 97 00:08:15,700 --> 00:08:27,920 I'm gonna come down here, on line 23, else colon print parentheses Please enter h, l or c. 98 00:08:27,920 --> 00:08:29,500 So if they do anything else, we just remind 99 00:08:29,500 --> 00:08:32,349 them what the three options are. Alright, so I'm going to stop the video here and 100 00:08:32,349 --> 00:08:35,740 in the next one, we'll look at why we've got those errors. 101 00:08:35,740 --> 00:08:38,820 See you in the next video.