WEBVTT 0 00:00.110 --> 00:02.300 Now we're really close to the finish line. 1 00:02.300 --> 00:06.200 I know today is quite a long day, but just bear in there, 2 00:06.200 --> 00:08.300 you're going to get there really, really soon. 3 00:08.300 --> 00:13.310 So the last part of our Caesar Cipher just has three TODOs. 4 00:13.310 --> 00:18.980 One is we need to import and print the logo from this file, art.py. 5 00:19.220 --> 00:25.790 And then we have to figure out, well, what happens if the user enters a number or space. 6 00:25.790 --> 00:33.290 So if you take a look at the final, demo and we were to write a message, say "hello," and then we add 7 00:33.290 --> 00:41.600 some numbers or some symbols, we don't want those to be lost when we encode the message, 8 00:41.600 --> 00:42.050 right? 9 00:42.050 --> 00:48.410 So what we want instead is we only want to encode the alphabetical letters. 10 00:48.410 --> 00:55.820 And then for anything that is not within the alphabet, we just keep it as it is and add it to the final 11 00:55.820 --> 00:57.380 encoded result. 12 00:57.410 --> 01:03.440 This way we can encode and decode and keep any of these characters the user types in. 13 01:03.440 --> 01:12.080 And then finally we need a way for our program to rerun once the user is done with encoding or decoding. 14 01:13.220 --> 01:17.690 So that way we ask them, "Type 'yes' if you want to go again. 15 01:17.690 --> 01:19.270 Otherwise type 'no'." 16 01:19.270 --> 01:24.040 And if they type yes then they get to encode_or_decode again. 17 01:24.040 --> 01:28.720 And once they're actually done then they could type 'no', 18 01:28.720 --> 01:33.220 and the program just says, 'Goodbye' like a good little robot. 19 01:33.220 --> 01:35.500 So those are the three TODOs, 20 01:35.500 --> 01:37.660 have a look in the Description box, 21 01:37.660 --> 01:44.710 have a look at the hints if you need them, and go ahead and pause the video and complete the final 22 01:44.710 --> 01:47.260 part of the Caesar Cipher project. 23 01:53.680 --> 01:57.970 Okay, hopefully, it was straightforward and you're just here to check the solution. 24 01:57.970 --> 02:03.160 If not, don't worry, I'm going to walk through everything and explain everything anyways, so hopefully 25 02:03.160 --> 02:05.140 it'll be a lot more clear afterwards. 26 02:05.140 --> 02:07.300 So TODO one is pretty simple, 27 02:07.300 --> 02:14.830 All we need to do is import the module art and then just simply print(art.logo), which is the name 28 02:14.830 --> 02:16.540 that we've got in here. 29 02:16.540 --> 02:18.160 That's the name of the variable. 30 02:18.160 --> 02:26.020 And that's going to print out that Caesar Cipher logo with ASCII art every time we start our program. 31 02:26.020 --> 02:29.860 Now you can also do the previous from import, 32 02:29.860 --> 02:33.040 but this is also clear enough as well. 33 02:33.220 --> 02:40.480 Now TODO Number 2, we need to figure out what to do if the user enters a number, or symbol, or space, 34 02:40.480 --> 02:46.210 and how can we keep hold of it when they actually type that in. 35 02:46.210 --> 02:52.900 So let's think about where we would make that differentiation every time we loop through each of the 36 02:52.900 --> 02:59.560 letters, if that letter that we're looping through from the original_text happens to be not something 37 02:59.560 --> 03:05.260 that exists in this list of alphabet, then it's probably a symbol or a number or something that we 38 03:05.260 --> 03:07.090 can't shift very easily. 39 03:07.090 --> 03:13.990 So then we probably want to bypass the rest of this and do something separate. 40 03:14.890 --> 03:25.480 So what we can do is we can say if the letter is not in the alphabet list, then in that case, all 41 03:25.480 --> 03:31.900 we're going to do is simply take the output_text += the current letter. 42 03:31.900 --> 03:39.070 And this will add whatever letter it is that we need to skip into the output_text as its original format. 43 03:39.070 --> 03:46.140 But then we can have an else statement and have the rest of this carryout 44 03:46.140 --> 03:53.040 if this is not the case, which means the letter is in the alphabet and we can in fact shift it. 45 03:53.040 --> 03:59.010 Now, another way that we could do this is we could add a bunch of symbols and numbers to our alphabet 46 03:59.010 --> 04:02.340 list, and instead of calling it alphabet, call it something else, 47 04:02.340 --> 04:04.740 and that way we can be more inclusive. 48 04:04.740 --> 04:09.330 But it's quite hard to include all of the symbols and all of the numbers. 49 04:09.330 --> 04:15.720 And just to keep it simple for this practice exercise, this is probably the most straightforward solution. 50 04:16.260 --> 04:19.530 So now we're on to TODO Number 3, 51 04:19.530 --> 04:22.860 can you figure out a way to restart the Cipher program. 52 04:22.860 --> 04:28.470 So as previous, the way that we need to do this is to use a while loop. 53 04:28.470 --> 04:34.170 So if we have some sort of variable let's call it should_continue, 54 04:34.740 --> 04:42.510 and we set it to true because normally while the program is going, it should in fact continue asking 55 04:42.510 --> 04:45.120 the user, do you want to go again? 56 04:45.120 --> 04:46.380 Do you want to go again? 57 04:46.380 --> 04:49.530 But sometimes the user will say, no. 58 04:49.530 --> 04:54.690 So let's go ahead and create a while loop that checks for this variable. 59 04:54.690 --> 05:00.960 And if it is the case, then we're going to keep running all of these inputs, asking them direction, 60 05:00.960 --> 05:04.290 text, shift and also running our ceasar() function. 61 05:04.290 --> 05:12.060 But then at the end of all of that, once we've given them the encoded_or_decoded text and that caesar() 62 05:12.060 --> 05:19.860 function has come to an end, then the next thing we're going to do is we're going to check with them 63 05:19.860 --> 05:22.020 whether if they want to go again. 64 05:22.020 --> 05:26.430 So I'm going to copy this message and add it into an input. 65 05:27.330 --> 05:38.280 So in this input, I'm going to go ahead and change it to .lower() to make sure that we've got 66 05:38.280 --> 05:45.660 the...whatever it is they type capital, or no capital set to the same thing so that we can check it more 67 05:45.660 --> 05:46.440 easily. 68 05:46.440 --> 05:55.890 And I'm also just going to add a \n so that our cursor goes on to the next line when they do 69 05:55.890 --> 06:00.510 have to type, so that its cursor here rather than cursor here. 70 06:00.840 --> 06:05.850 Now finally I'm going to save that input into a variable called restart. 71 06:05.850 --> 06:14.600 And now we can check the value of that restart. If restart is equal to "no", 72 06:14.630 --> 06:20.600 well, in that case, we can change our should continue to False. 73 06:20.600 --> 06:25.070 And then we can print ("Goodbye"). 74 06:25.070 --> 06:28.550 And if the restart is any other value. 75 06:28.550 --> 06:30.680 So 'yes', or capital 76 06:30.680 --> 06:34.550 'Yes', or whichever then this if statement is skipped, 77 06:34.550 --> 06:38.660 and our while loop loops back up from the start. 78 06:38.660 --> 06:48.440 So that is how we can make sure that our code continues asking the user for a message and their encoding 79 06:48.440 --> 06:49.580 or decoding. 80 06:49.580 --> 06:53.630 And it will continue forever until they basically say, 'no'. 81 06:53.720 --> 07:01.580 Now, if you've been following my code all along, I want you to try and test your code right now repeatedly, 82 07:01.580 --> 07:05.300 and see if you can spot a crucial bug. 83 07:05.330 --> 07:12.380 Now it relates to this caesar() function, and I want you to see if you can, through testing, figure 84 07:12.380 --> 07:14.960 out what is wrong and solve the issue. 85 07:14.990 --> 07:16.520 So pause the video now. 86 07:18.860 --> 07:21.110 So did you manage to find the problem? 87 07:21.140 --> 07:22.610 Here, let me show you. 88 07:22.610 --> 07:31.730 So if I go ahead and start encoding and we decide to type a and b, and then type the shift to go up by 89 07:31.730 --> 07:35.060 2, so that becomes cd, which is great. 90 07:35.060 --> 07:36.440 So let's go again. 91 07:36.440 --> 07:45.470 And let's now type decode and again use the previous cyber_text which is CD. 92 07:45.800 --> 07:50.090 And if we take our cipher_text and shift it down by 2, 93 07:50.120 --> 07:57.860 we should expect ab, which is our original message which we encoded up here, but instead we get an 94 07:57.860 --> 07:58.340 f. 95 07:58.340 --> 08:00.530 So what is going on? 96 08:00.560 --> 08:11.120 Well, if you debug either using the debugger or your own knowledge, you'll find that this line here 97 08:11.120 --> 08:12.650 is the culprit. 98 08:13.220 --> 08:19.730 We're determining the shift-amount by shifting it back to the negative, 99 08:19.730 --> 08:22.370 and that's what happens when we do -1. 100 08:22.490 --> 08:30.860 But this is inside the for loop, which means that it's going to happen and flip every single time the 101 08:30.860 --> 08:32.120 for loop runs. 102 08:32.120 --> 08:40.690 So in order to fix this, what we need to do is just to take it out of the for loop and then put it 103 08:40.690 --> 08:42.340 above the for loop. 104 08:42.340 --> 08:48.280 And now if we retest, you'll see we've managed to solve that problem. 105 08:48.490 --> 08:54.220 So going up works, and going down also works. 106 08:54.910 --> 09:01.030 So that is all there is to it to this three-part Caesar Cipher project. 107 09:01.030 --> 09:07.450 And of course, as always with all of these projects, feel free to add modifications, tackle any edge 108 09:07.450 --> 09:12.460 cases, there might be things that I haven't thought of, that you've thought of, it might be improvements 109 09:12.460 --> 09:13.420 you want to make. 110 09:13.450 --> 09:18.940 The program is yours, so you can do whatever it is you want to do to improve it. 111 09:18.940 --> 09:26.590 And hopefully in the process, you've managed to solidify and revise some of the topics that we've learned 112 09:26.590 --> 09:29.170 in today and previous lessons. 113 09:29.170 --> 09:32.440 And if it was really, really hard, then that's a good thing. 114 09:32.440 --> 09:37.540 That means you really struggled and you're building those programming muscles, right? 115 09:37.540 --> 09:41.200 There's no point going to the gym and lifting one kilogram weights. 116 09:41.200 --> 09:44.530 It's not going to make you very muscular. 117 09:44.530 --> 09:47.650 We got to push ourselves and this is okay. 118 09:47.650 --> 09:51.940 So I hope you had fun with me today and I look forward to seeing you tomorrow.