1 00:00:05,220 --> 00:00:08,850 Welcome everyone to this lecture on variables and not PI files. 2 00:00:10,020 --> 00:00:15,090 So in this lecture, we're going to cover the very basics of running a Dart Pi or Python extension file, 3 00:00:15,480 --> 00:00:19,590 then we'll talk about printing results out so you can actually see results in your command line. 4 00:00:19,920 --> 00:00:22,430 Then we'll talk about just basic arithmetic with Python. 5 00:00:22,440 --> 00:00:26,370 What are the symbols you should know, as well as variable assignment how that works of Python? 6 00:00:26,790 --> 00:00:27,870 OK, let's get started. 7 00:00:28,140 --> 00:00:30,630 I'm going to go and open up visual studio code. 8 00:00:31,110 --> 00:00:33,450 OK, here I am in a Visual Studio code. 9 00:00:33,840 --> 00:00:39,000 Now, if you skip all the way to this section of the course, please make sure you watch the installation 10 00:00:39,000 --> 00:00:44,160 and setup for Visual Studio code, or you talk about setting up and installing Python with Visual Studio 11 00:00:44,160 --> 00:00:45,750 code, as well as setting up your terminal. 12 00:00:46,260 --> 00:00:51,360 What we're going to do right now is just set up a terminal instance inside Visual Studio code so we 13 00:00:51,360 --> 00:00:53,400 can actually run a Python file. 14 00:00:53,820 --> 00:00:57,660 So I'm going to hit Terminal here and I can open up a new terminal. 15 00:00:58,170 --> 00:01:03,540 You should notice that if you're on a Windows computer, this will by default open up Windows PowerShell. 16 00:01:03,840 --> 00:01:07,230 Sometimes this actually has issues of Python, depending how you install it. 17 00:01:07,500 --> 00:01:11,880 These days, it should normally work, but just in case what I'm going to do is, I'm actually going 18 00:01:11,880 --> 00:01:15,510 to open up my command prompt if you're only Mac OS or Linux. 19 00:01:15,780 --> 00:01:20,180 This should pretty much open what's known as your Mac OS or Linux Terminal, and you should be OK. 20 00:01:20,190 --> 00:01:21,390 You don't need to actually do this step. 21 00:01:21,420 --> 00:01:22,590 This is just for Windows users. 22 00:01:22,920 --> 00:01:28,740 You click over here on this little power down, not the plus sign, but the dropdown and then hit command 23 00:01:28,740 --> 00:01:29,160 prompt. 24 00:01:29,550 --> 00:01:32,250 And it's now going to open up command prompt or seemed. 25 00:01:32,700 --> 00:01:35,820 And a Mexican then put the little trashcan here to delete the PowerShell. 26 00:01:36,180 --> 00:01:36,480 OK. 27 00:01:36,870 --> 00:01:39,840 So I have my command prompt opened up. 28 00:01:40,290 --> 00:01:45,900 And then notice it's opened up at the same location where I've been on my desktop underneath Django 29 00:01:45,900 --> 00:01:46,470 lectures. 30 00:01:47,400 --> 00:01:54,150 So what I'm going to do is at Django Lectures, I will create a new file and I will call this example. 31 00:01:54,660 --> 00:01:58,290 But now it's going to have the extension dot pi and notice. 32 00:01:58,290 --> 00:02:03,600 Now Visual Studio code is smart enough to understand, OK, this is a Python file because it has Dot 33 00:02:03,600 --> 00:02:09,090 Pi and I'm going to collapse the explorer here and let me show you how to run Python at your terminal, 34 00:02:09,360 --> 00:02:12,810 as well as run a Python script at your terminal. 35 00:02:13,260 --> 00:02:16,230 So Python does have the ability to be run at the command line. 36 00:02:16,350 --> 00:02:22,290 And if you were just to type in Python like this and then hit Enter, once you have Python installed, 37 00:02:22,560 --> 00:02:27,960 you're going to see this output here, which allows you to run Python commands, so you'd actually be 38 00:02:27,960 --> 00:02:33,750 able to do something like one plus one hit enter and see the result of two. 39 00:02:34,170 --> 00:02:38,100 Now, typically, we're not actually going to be using the terminal because I would have to enter all 40 00:02:38,100 --> 00:02:39,750 my code line by line by line. 41 00:02:40,110 --> 00:02:43,380 I'd rather have it all in a nice script and then just run the entire script. 42 00:02:43,770 --> 00:02:45,690 So if you want to quit out of this? 43 00:02:47,100 --> 00:02:52,300 You can say quit open, close parentheses there, enter and notice I'm no longer running Python. 44 00:02:52,320 --> 00:02:57,240 So if you ever see yourself having some output like this where it says the version of Python when you 45 00:02:57,240 --> 00:03:02,280 installed it and then something like tape help copyright and you meant to actually run a file, go ahead 46 00:03:02,280 --> 00:03:03,510 and run quit first. 47 00:03:04,380 --> 00:03:06,300 And if you're on windows, you want to clear the screen. 48 00:03:06,630 --> 00:03:09,750 You can type seals if you're on Mac OS or Linux, it's just clear. 49 00:03:10,170 --> 00:03:12,030 So seals here to clear that. 50 00:03:12,360 --> 00:03:18,730 OK, so let's go ahead and explore how to actually run Python code within our PI file. 51 00:03:19,440 --> 00:03:20,990 So how can I do this? 52 00:03:21,000 --> 00:03:25,290 What I'm going to do is I'm pretty zoomed in here, but I was going to type in one. 53 00:03:26,610 --> 00:03:27,210 Plus one. 54 00:03:28,780 --> 00:03:32,710 I'm going to save that change, and I'm going to show you kind of a common and beginner mistake before 55 00:03:32,720 --> 00:03:33,770 actually should have fixed this. 56 00:03:34,120 --> 00:03:38,890 So a lot of times beginners have some sort of logic here, like one plus one and they want to run this 57 00:03:38,890 --> 00:03:39,680 Python script. 58 00:03:39,700 --> 00:03:46,210 So what they say is they come here and then they say Python space and then example that pie. 59 00:03:46,300 --> 00:03:48,190 This is actually how you run the Python script. 60 00:03:48,220 --> 00:03:52,480 This is saying using Python, execute this that file. 61 00:03:52,780 --> 00:03:58,900 Notice this That pie file is currently located at this location underneath desktop jingle lectures. 62 00:03:59,290 --> 00:04:04,150 If I were to just enter right now, it would run the file, but I wouldn't see the output. 63 00:04:04,180 --> 00:04:07,030 A lot of times students expect, Hey, where's the two? 64 00:04:07,450 --> 00:04:12,190 Well, the reason you're not seeing anything is because with Python, you have to be explicit about 65 00:04:12,190 --> 00:04:14,230 what you want to show as output. 66 00:04:14,590 --> 00:04:16,959 And in that case, you're going to need to say print. 67 00:04:18,110 --> 00:04:20,510 Open close parentheses, one plus one. 68 00:04:21,019 --> 00:04:23,870 Go ahead and save that change, remember to save it, there's a little circle here. 69 00:04:24,080 --> 00:04:28,400 Another really common mistake by beginners is they kind of forget to save their changes here and then 70 00:04:28,400 --> 00:04:29,480 run that code again. 71 00:04:29,600 --> 00:04:30,980 A shortcut for running the same code. 72 00:04:30,980 --> 00:04:35,410 If you go up Arrow, you get to see the history of commands put to the terminal so you can keep doing 73 00:04:35,420 --> 00:04:36,770 up errors or down errors. 74 00:04:37,340 --> 00:04:38,390 So I'm going to run Python. 75 00:04:38,390 --> 00:04:39,440 Example that pi again. 76 00:04:40,040 --> 00:04:42,910 I hit there and now I actually see the result, too. 77 00:04:43,670 --> 00:04:46,820 So I see two because I said print one plus one. 78 00:04:47,150 --> 00:04:52,850 So now that we understand how to run a python file, let's go ahead and run through some arithmetic. 79 00:04:52,910 --> 00:04:56,570 The last thing I want to show you is a real quick example of a common mistake. 80 00:04:56,570 --> 00:04:57,920 I see beginners do all the time. 81 00:04:58,190 --> 00:04:59,930 A lot of times they accidentally do this. 82 00:04:59,990 --> 00:05:03,780 They type Python enter, and now they're actually running Python. 83 00:05:03,800 --> 00:05:07,190 And then they try to do something like this python example that python. 84 00:05:07,190 --> 00:05:09,320 They hit enter and then they get this syntax error. 85 00:05:09,560 --> 00:05:14,840 That's because Python thinks you're actually trying to run Python code instead of using Python to execute 86 00:05:14,840 --> 00:05:15,710 that that file. 87 00:05:15,950 --> 00:05:16,930 So just be careful of this. 88 00:05:16,940 --> 00:05:19,820 I see a lot of beginners using Python X to make this mistake. 89 00:05:20,120 --> 00:05:24,200 So just keep that in mind if you ever see something like this because you accidentally are running the 90 00:05:24,200 --> 00:05:28,310 Python interpreter at the command line instead of executing the actual that file. 91 00:05:28,520 --> 00:05:29,630 So now I'm going to. 92 00:05:30,610 --> 00:05:31,900 Quit this, OK? 93 00:05:31,930 --> 00:05:33,100 And let's clear that out. 94 00:05:34,180 --> 00:05:35,440 Oops, see less. 95 00:05:36,190 --> 00:05:36,640 There we go. 96 00:05:37,180 --> 00:05:41,530 OK, so I can't add numbers by just saying something like one plus one. 97 00:05:42,070 --> 00:05:48,880 And if I say Python, example that pi, I can keep executing to see the results here if I want to multiply. 98 00:05:49,180 --> 00:05:53,800 Then that's going to be an Asterix site so I can say 20 Asterix times. 99 00:05:53,800 --> 00:05:55,760 20 save that change. 100 00:05:55,780 --> 00:05:57,450 And now this should be 400. 101 00:05:57,460 --> 00:05:58,500 So you see the result there. 102 00:05:59,080 --> 00:06:02,290 Other commands you may want to know is a minus for subtraction. 103 00:06:02,330 --> 00:06:05,800 So basically, what you would expect, it's going to be zero there. 104 00:06:06,280 --> 00:06:11,000 If you have something like exponential powers, that's going to be two Asterix signs. 105 00:06:11,020 --> 00:06:12,370 It's not a carrot symbol. 106 00:06:12,790 --> 00:06:19,450 So if you want to to the power of three, it's going to be two asterisks and then two, the power three 107 00:06:19,450 --> 00:06:21,310 there saved that change. 108 00:06:22,420 --> 00:06:25,420 And then you can go ahead and run it here and you see it's eight. 109 00:06:25,780 --> 00:06:26,140 OK. 110 00:06:26,650 --> 00:06:29,410 And then keep in mind, order of operations are followed. 111 00:06:29,680 --> 00:06:34,000 So you can have some sort of formula here inside the print statement so you can use parentheses for 112 00:06:34,000 --> 00:06:34,240 that. 113 00:06:35,470 --> 00:06:39,820 Hopefully not too confusing using so many ways, but you can do something like do two percent first 114 00:06:40,240 --> 00:06:45,250 and then multiply it by the result of, let's say, 10 plus three. 115 00:06:45,280 --> 00:06:48,160 This is just to give you a little bit of lingo into logic. 116 00:06:48,610 --> 00:06:55,000 And then if you run into that, you can say it's 156, essentially saying it's going to execute 12 times 117 00:06:55,000 --> 00:06:55,640 13. 118 00:06:55,660 --> 00:06:57,400 So order of operations there? 119 00:06:57,820 --> 00:06:58,180 OK. 120 00:06:58,750 --> 00:07:02,270 So it's going to get a little annoying to have to keep writing all these numbers. 121 00:07:02,350 --> 00:07:05,770 Typically, what you want to do is actually use variable assignments. 122 00:07:05,890 --> 00:07:12,070 So instead of saying two plus 10 or 10 plus three, usually these four numbers are referring to Real-World 123 00:07:12,070 --> 00:07:12,550 things. 124 00:07:12,730 --> 00:07:16,870 So to do a variable assignment, you use a single equals sign. 125 00:07:17,260 --> 00:07:24,190 So how do we do that kind of cleared my terminal here, span this and then inside example that PI, 126 00:07:24,550 --> 00:07:27,430 I'm going to create a very simple idea. 127 00:07:27,430 --> 00:07:35,800 Let's imagine I have my income and my income is $100, and I want to figure out what I pay in taxes. 128 00:07:36,010 --> 00:07:41,560 And let's say my tax rate is going to be equal to 10 percent or zero point one for variable assignment 129 00:07:41,560 --> 00:07:42,220 with Python. 130 00:07:42,520 --> 00:07:47,740 The variables are going to follow what's known as snake casing, where every single kind of separate 131 00:07:47,740 --> 00:07:49,960 word here is split up with an underscore. 132 00:07:50,290 --> 00:07:52,210 And then you choose your variable name. 133 00:07:52,270 --> 00:07:57,730 Notice how when I hover over it at Visual Studio Code actually tells me, Hey, this is a variable and 134 00:07:57,730 --> 00:08:00,160 it's equal to 100, so that's perfect. 135 00:08:00,670 --> 00:08:02,500 Then what I can do is say tax rate. 136 00:08:04,000 --> 00:08:06,040 That's a new variable on a new line. 137 00:08:06,580 --> 00:08:08,410 And then that's going to be equal to zero point one. 138 00:08:09,660 --> 00:08:15,660 Then I'm going to enter here and I'm going to actually assign a new variable for my own taxes. 139 00:08:15,900 --> 00:08:20,230 So this is what taxes I would owe and that would simply be equal to my income. 140 00:08:20,250 --> 00:08:24,590 And notice visual studio code actually starts kind of auto completing and helping you hear something 141 00:08:24,600 --> 00:08:24,840 to say. 142 00:08:24,840 --> 00:08:26,670 My income multiplied. 143 00:08:26,670 --> 00:08:27,510 That's an asterisk. 144 00:08:27,810 --> 00:08:28,320 Times. 145 00:08:29,890 --> 00:08:30,460 My tax rate. 146 00:08:31,240 --> 00:08:37,960 OK, so again, what's happening here is I'm using variables now to actually run this and then I have 147 00:08:37,960 --> 00:08:43,659 my taxes is equal to my income times tax rate, so I have a little pop quiz for you. 148 00:08:44,140 --> 00:08:46,330 If I were to save these changes. 149 00:08:47,600 --> 00:08:49,520 And run python example that pie. 150 00:08:49,790 --> 00:08:51,230 What would I see as the output? 151 00:08:52,190 --> 00:08:56,240 Now, if you said you would see 10, you're actually incorrect. 152 00:08:56,510 --> 00:08:59,720 Remember, I need to print something if I want to see the output. 153 00:08:59,870 --> 00:09:03,080 If I just run python, example that pie, I get no output. 154 00:09:03,240 --> 00:09:04,340 Common beginner mistake. 155 00:09:04,730 --> 00:09:07,070 Well, we need to do is come here and say print. 156 00:09:09,740 --> 00:09:16,640 My taxes saved that change and then run this, and you can see now I have 10 here. 157 00:09:17,030 --> 00:09:21,800 And if you're wondering why it says ten point zero instead of just 10, that's because there's a difference 158 00:09:21,800 --> 00:09:26,330 here between my income and tax rate as far as arithmetic or no type. 159 00:09:26,660 --> 00:09:29,150 This is what's known as an integer, just a whole number. 160 00:09:29,450 --> 00:09:35,270 And this is known as a floating point number, which means it has specificity past the actual decimal 161 00:09:35,270 --> 00:09:35,660 point. 162 00:09:35,930 --> 00:09:41,570 And when you begin to do arithmetic operations between an integer and a floating point number, it's 163 00:09:41,570 --> 00:09:45,980 just going to have the result be a floating point number like ten point zero instead of ten. 164 00:09:46,010 --> 00:09:49,580 This is going to show you that extra information for pretty much all our use cases. 165 00:09:49,580 --> 00:09:53,660 We don't really care about this, whether it's 10 or ten point zero, and we don't really care too much 166 00:09:53,660 --> 00:09:56,060 about the difference between integers and floating point numbers. 167 00:09:56,300 --> 00:09:58,490 We just care that the mathematics makes sense here. 168 00:09:58,670 --> 00:10:02,060 So that's the very basics of running a python file. 169 00:10:02,330 --> 00:10:07,460 Setting up variables and also the very basics of arithmetic and printing your output. 170 00:10:07,790 --> 00:10:09,980 And that's pretty much all we need to know so far. 171 00:10:10,310 --> 00:10:15,410 Coming up next, we're going to do is have a discussion on strings and different properties about strings. 172 00:10:15,740 --> 00:10:16,340 I'll see you there.