WEBVTT 0 00:00.200 --> 00:04.370 Now, in this lesson, I want to talk to you about Python variables, 1 00:04.370 --> 00:06.980 and it's a really, really useful concept. 2 00:06.980 --> 00:15.140 The first thing I want to do is to take a look at this line of code that you should have already, and 3 00:15.140 --> 00:18.770 when we run this, we should be pretty familiar with what happens, right? 4 00:18.770 --> 00:23.300 It will ask us for our name and when we hit Enter, nothing happens, 5 00:23.300 --> 00:31.760 but behind the scenes, this name or this input has now been received by this function. 6 00:31.760 --> 00:36.830 But once that's done, it kind of just disappears, right? 7 00:36.830 --> 00:41.690 And there's no way for us to be able to refer to it in the future. 8 00:42.320 --> 00:43.580 Or is there? 9 00:45.260 --> 00:48.710 Well, this is where variables come in really handy, 10 00:48.770 --> 00:53.060 if I give the result of this action, a name, well, 11 00:53.060 --> 00:55.700 then I'll be able to refer to it later on. 12 00:55.730 --> 01:02.300 So at the beginning of the line, I'm going to call it name, and then I'm going to add an equal sign, 13 01:02.300 --> 01:10.820 and what this does is it assigns whatever it is that the user typed in as the input to this prompt to 14 01:10.820 --> 01:13.640 a variable called name. 15 01:14.570 --> 01:21.700 So now if I go ahead and run my code again and I enter a name. 16 01:22.210 --> 01:28.630 Now, once I hit Enter, normally there's no way for me to get hold of this anymore, right? 17 01:28.660 --> 01:32.740 But now I can actually go ahead and write 18 01:32.740 --> 01:33.520 print, 19 01:33.520 --> 01:37.360 I'm going to print the value of this variable name. 20 01:37.480 --> 01:42.980 So now if I run my code and I write a name, hit Enter, 21 01:42.980 --> 01:45.500 you'll see that this gets printed. 22 01:45.500 --> 01:55.280 And I can use this at any point in my code just by referring to the name that's attached to this value. 23 01:55.940 --> 02:03.500 So it's almost like we've saved the data from this action to a name. 24 02:03.890 --> 02:10.800 And if you think about it, if you had a phone book, let's say, and you just jotted down the numbers 25 02:10.800 --> 02:17.880 of people, the next time you look at this, there's no way for you to know whose number that is, right? 26 02:18.060 --> 02:21.330 In a sense, it's the same thing with the computer, 27 02:21.330 --> 02:28.410 even though we've inputted this piece of data, there's no way for us to be able to refer to this data 28 02:28.410 --> 02:30.980 unless we give it a name. 29 02:30.980 --> 02:38.390 So in our phone book, we might say that this particular number is associated with the name James. 30 02:38.390 --> 02:43.370 And in programming, we would call this name, james, a variable. 31 02:43.640 --> 02:49.280 So we could write something like James =, and then his phone number. 32 02:49.640 --> 02:56.290 And this means that in the future, if we ever need this piece of data, we can just refer to it by 33 02:56.290 --> 02:57.130 its name, 34 02:57.520 --> 02:59.380 the variable name of james. 35 02:59.950 --> 03:08.470 Now, as the name variable suggests, it's something that can be changed or can be varied. 36 03:08.500 --> 03:15.400 So for example, just because this name is set to something up here doesn't mean that I can't change 37 03:15.400 --> 03:16.450 it later on. 38 03:16.480 --> 03:20.810 So to make things simple, let's go ahead and delete the input() function, 39 03:20.810 --> 03:24.740 and let's just say name is equal to jack. print("name"). 40 03:24.740 --> 03:31.520 When I run that, jack is what gets printed inside the console, because I'm now referring to that piece 41 03:31.520 --> 03:34.100 of data by the variable name. 42 03:34.370 --> 03:42.710 But if later on I decide to give this variable a different piece of data to hold on to, let's say, 43 03:42.800 --> 03:50.010 Angela, and I print(name) at this time point after I've changed it, 44 03:50.010 --> 03:53.640 what do you think these two lines will print? 45 03:53.640 --> 03:55.740 What do you think will first be printed? 46 03:55.740 --> 03:57.840 What do you think will be printed second? 47 03:58.350 --> 04:06.390 So even though they're both printing the same variable at this point, when we first call print, it's 48 04:06.390 --> 04:08.480 holding on to the value of jack, 49 04:08.480 --> 04:14.780 but by Line 5, I've now changed it so that it's holding on to the value of Angela. 50 04:16.340 --> 04:20.420 So to practice that, I have a challenge for you. 51 04:20.420 --> 04:29.690 So I want you to be able to figure out how many characters are in the name that the user types in using 52 04:29.690 --> 04:33.420 the input() function. So you already know how the input function works, 53 04:33.420 --> 04:39.630 you already know how to get the user to enter it, and then to get that data back into our code and 54 04:39.630 --> 04:40.410 print it out, 55 04:40.410 --> 04:42.330 but here's the extra step, 56 04:42.330 --> 04:47.700 "Can you calculate how many characters there are in the name that they type in?" 57 04:47.700 --> 04:50.520 For example, if they typed in jack, that would be four. 58 04:50.520 --> 04:53.310 If they typed in Angela that would be six. 59 04:53.310 --> 04:58.880 Now how do we figure out things when we're programming and we're trying to do something that we haven't 60 04:58.880 --> 04:59.720 done before? 61 04:59.750 --> 05:04.910 Well, one of the most important skills as a programmer is to be able to use Google well. 62 05:04.910 --> 05:10.280 It's to be able to find the answers that you need because it's inevitable that you won't remember 63 05:10.280 --> 05:14.390 every single function and you won't know every single function. 64 05:14.390 --> 05:19.070 So we need to read documentation and we need to know how to get hold of it. 65 05:19.070 --> 05:20.570 So very simple, 66 05:20.620 --> 05:26.530 we start off with our query, "how to find the length of a string." 67 05:26.530 --> 05:31.840 And then we add our programming language because this will be different in every programming language. 68 05:31.840 --> 05:34.540 So I normally just add Python to the end of it. 69 05:34.540 --> 05:40.210 And then once we hit Enter, normally we'll get hold of some form of documentation, 70 05:40.210 --> 05:44.080 and the W3Schools documentation for Python is not bad. 71 05:44.080 --> 05:48.110 And you can also browse through all of the other examples. 72 05:48.110 --> 05:52.820 So normally for Python, I stick to W3Schools or StackOverflow, 73 05:52.820 --> 05:55.490 and both of these will give you the right answer. 74 05:55.490 --> 06:02.060 But if we are reading documentation then you can see that normally there is a whole bunch of other things 75 06:02.060 --> 06:05.990 that we can look up, just like a dictionary of Python. 76 06:05.990 --> 06:10.890 Now, as you wouldn't start with a dictionary when you're learning a new language, 77 06:10.890 --> 06:11.940 believe me, I tried that, 78 06:11.940 --> 06:12.900 it did not work, 79 06:12.900 --> 06:19.560 you also wouldn't want to learn through everything in the documentation because it's very dry. 80 06:19.560 --> 06:25.350 And when you don't have a real-life application, when you're not trying to use a particular function 81 06:25.350 --> 06:29.100 or some sort of component, then you also don't remember it very well. 82 06:29.100 --> 06:34.130 So I recommend to find what you need when you need it, 83 06:34.130 --> 06:37.460 and our brain is for thinking and not for storing, 84 06:37.460 --> 06:44.390 because these days, as you know, it's super cheap to buy a single terabyte, storage hard disk 85 06:44.390 --> 06:45.320 online. 86 06:45.320 --> 06:50.210 I think it costs something like 10 or $20 and it's just getting cheaper every day. 87 06:50.210 --> 06:52.850 So don't use your brain to store things, 88 06:52.850 --> 06:53.750 use it to think. 89 06:53.750 --> 07:00.580 But coming back to our documentation here, in order to get the Python string length, we use the len() 90 07:00.580 --> 07:01.180 function. 91 07:01.180 --> 07:04.690 And just like the print() function, it's an inbuilt function in Python, 92 07:04.690 --> 07:07.210 so we can simply just write len(), 93 07:07.210 --> 07:10.780 and then we can use whatever it is we want to measure. 94 07:10.780 --> 07:19.180 For example, in this case it's, "Hello world!" and it will output the number of characters in that string. 95 07:19.240 --> 07:22.220 So now give it a go yourself. 96 07:22.430 --> 07:26.330 So the pause one is the instruction set. 97 07:26.330 --> 07:29.720 And I want you to get user input. 98 07:29.720 --> 07:35.900 I want you to take that user input and calculate the length of the string that the user inputted, 99 07:35.900 --> 07:40.280 and finally to print that number out into the output area. 100 07:40.280 --> 07:44.030 And everything could be done in just one line of code. 101 07:44.030 --> 07:49.570 So try to find the documentation, try to figure out how to do this, and I'll see you on the other 102 07:49.570 --> 07:51.100 side where we run through the solution. 103 07:51.100 --> 07:52.420 So pause the video now. 104 07:55.270 --> 07:55.810 All right. 105 07:55.810 --> 08:00.670 So referring to the documentation it's pretty straightforward. 106 08:00.670 --> 08:04.480 The first thing we're going to do is we're going to get hold of the input. 107 08:04.480 --> 08:07.240 So we know the input function looks like this, 108 08:07.240 --> 08:09.670 and we can add in whatever prompt we want. 109 08:09.670 --> 08:12.350 So what is your name? 110 08:12.740 --> 08:18.590 And then we're going to wrap this input inside another set of parentheses. 111 08:18.590 --> 08:22.520 And you can do that without having to type open and closing brackets, 112 08:22.520 --> 08:27.440 if you just highlight the entire line you want to wrap and then type the open bracket, 113 08:27.440 --> 08:30.200 and it should wrap everything inside. 114 08:30.200 --> 08:36.610 So the next step is to calculate the length which is using the len() function that we just heard about. 115 08:36.610 --> 08:41.440 And then finally I'm going to wrap everything in just one more bracket, 116 08:41.440 --> 08:44.320 and this one is the print() function. 117 08:44.320 --> 08:49.690 So the three steps are we get hold of the user input, 118 08:49.690 --> 08:53.530 we calculate the number of characters in that input, 119 08:53.530 --> 08:57.220 and then finally we print it out into the output area. 120 08:57.220 --> 08:59.990 So now let's go ahead and run our code. 121 08:59.990 --> 09:05.120 So first line that comes out is these two print statements from before. 122 09:05.120 --> 09:07.910 And then the third line asks me what is my name. 123 09:07.910 --> 09:12.470 And you can see the process is paused, waiting for me to type that in. 124 09:12.470 --> 09:20.060 And then once I hit Enter, that name is going to replace this part of our code and it's going to calculate 125 09:20.060 --> 09:20.810 the length. 126 09:20.810 --> 09:25.830 And then finally that length is going to be printed and we get 6, which is correct. 127 09:25.830 --> 09:28.650 That's the number of characters in my name. 128 09:28.740 --> 09:33.900 So hopefully you've learned a little bit about documentation and also search. 129 09:33.900 --> 09:38.730 And also the importance of being able to get your own answers as a programmer. 130 09:39.750 --> 09:43.260 So now I have another coding challenge for you. 131 09:43.290 --> 09:50.660 Can you use what you've learned about creating variables and using variables in order to take these 132 09:50.660 --> 09:58.250 two parts, the input() function, and the output of the len() function and store them in separate variables. 133 09:58.250 --> 10:06.020 So there should be a variable called username that will store whatever the user enters into the input 134 10:06.020 --> 10:06.830 area. 135 10:06.830 --> 10:13.350 And then using that variable you're going to create a variable called length to calculate the length 136 10:13.350 --> 10:14.760 of the username. 137 10:14.760 --> 10:24.750 So then instead of this combined print statement, we can end up with simply just printing length at the 138 10:24.750 --> 10:25.410 end. 139 10:25.410 --> 10:29.460 So that way we can get the same result as this, 140 10:29.460 --> 10:36.150 but we use several steps to get there by creating and using some variables. 141 10:36.170 --> 10:38.600 So give this a try. 142 10:38.630 --> 10:43.460 Pause the video and if it doesn't work, come back and we'll go through the solution together. 143 10:47.270 --> 10:47.840 Okay. 144 10:47.840 --> 10:53.330 So the first step is we're going to create our first variable which is called username. 145 10:53.330 --> 11:00.080 And this is simply going to be set to store whatever the user types into the input. 146 11:00.080 --> 11:03.820 And that will get stored under this reference username. 147 11:03.820 --> 11:08.560 And then we're going to use that to calculate the length of the username. 148 11:08.560 --> 11:17.440 But instead of putting the input into the length, we can now refer to it using our variable name, username. 149 11:17.440 --> 11:26.570 So now we can print this new variable that we created on Line 9 and through these three steps, we've 150 11:26.570 --> 11:31.880 made this one single line code hopefully a little bit easier to understand. 151 11:31.880 --> 11:34.250 So we get the username from the input, 152 11:34.250 --> 11:36.470 we calculate the length from the username, 153 11:36.470 --> 11:38.090 and then finally we print the length. 154 11:38.090 --> 11:42.230 And when we hit Run you'll see exactly the same thing happens. 155 11:42.230 --> 11:44.030 We get the same code. 156 11:44.300 --> 11:48.560 Now at this point, you might be wondering to yourself what exactly is the point of variables? 157 11:48.560 --> 11:53.730 We've just turned one very, very short line into three very long lines. 158 11:53.760 --> 11:57.300 Now, of course, we're working with very, very simple examples here. 159 11:57.300 --> 12:04.020 And it might be hard to see the exact use case, but as things get more complicated, you will be glad 160 12:04.020 --> 12:06.030 to know how to use variables. 161 12:06.030 --> 12:11.670 Even in this simple situation, you can see that instead of this line of code, having these three lines 162 12:11.670 --> 12:14.120 of code makes our code a lot more readable 163 12:14.120 --> 12:19.250 because we're labelling each step of our code, we're saying, well, from this line of code, we're 164 12:19.250 --> 12:24.140 going to get hold of the username, from this line of code, we're going to work out the length of the 165 12:24.140 --> 12:24.920 username. 166 12:24.920 --> 12:29.390 And then finally we're going to use that final variable and print it out. 167 12:29.420 --> 12:38.380 Now as things get more complex, and being able to split up code into smaller modules will become a 168 12:38.380 --> 12:39.400 lifesaver. 169 12:39.400 --> 12:46.780 So in the next lesson, I've got a coding exercise for you and hopefully through more and more examples, 170 12:46.780 --> 12:49.630 you'll see just how useful variables can be. 171 12:49.660 --> 12:56.710 Right now, bear with me and just try to learn to create variables and use variables, 172 12:56.710 --> 13:02.080 and I promise it's going to all become very, very clear very soon just how useful they are.