1 00:00:05,580 --> 00:00:08,100 Welcome back everyone to this lecture on numbers. 2 00:00:09,430 --> 00:00:13,480 As you previously mentioned there's two main number types in Python that we're going to be working with. 3 00:00:13,570 --> 00:00:17,920 And those are integers which are whole numbers and floating point numbers which are numbers of a decimal 4 00:00:17,920 --> 00:00:18,410 point. 5 00:00:18,610 --> 00:00:22,660 Let's explore just basic math with Python how we can treat Python as a calculator. 6 00:00:22,660 --> 00:00:27,280 And then after that for the second half of this lecture we're going to discuss and explore how we can 7 00:00:27,280 --> 00:00:29,290 create variables and assign them values. 8 00:00:29,440 --> 00:00:31,080 So let's head over to the text editor. 9 00:00:31,180 --> 00:00:31,560 All right. 10 00:00:31,570 --> 00:00:32,430 Open up Adam. 11 00:00:32,440 --> 00:00:34,290 I have an untitled file here. 12 00:00:34,480 --> 00:00:39,670 I need to say this as a PI file in order for Adam to understand it it's a python script so I can run 13 00:00:39,670 --> 00:00:40,300 it. 14 00:00:40,330 --> 00:00:47,110 So try this out in a say file then select Save As and underneath my desk top flask examples what I'm 15 00:00:47,110 --> 00:00:51,080 going to do is just say this as my example. 16 00:00:51,220 --> 00:00:55,630 Pi Pi is the extension for python files. 17 00:00:55,630 --> 00:01:01,420 Ok so now I see my example that pi and I'm going to quickly write some code here prince which will actually 18 00:01:01,420 --> 00:01:03,980 display the output of something if I don't have print. 19 00:01:04,000 --> 00:01:07,060 That means when I run the dot PI file I mean that see the output. 20 00:01:07,060 --> 00:01:09,850 So let's say it prints hello world. 21 00:01:09,850 --> 00:01:11,990 So that's a string which you're going to get on later. 22 00:01:12,100 --> 00:01:17,410 But for right now just go ahead and say print open print sees either single or double quotes and then 23 00:01:17,440 --> 00:01:18,300 hello world. 24 00:01:18,430 --> 00:01:22,100 Single or double quotes make sure they match and then print CS OK. 25 00:01:22,360 --> 00:01:25,880 And then over here at the bottom I'm going to open up a new terminal. 26 00:01:26,000 --> 00:01:30,920 If you don't have this ability to open up a new terminal go back and check out our installation lecture 27 00:01:30,920 --> 00:01:31,880 and set up lecture. 28 00:01:31,940 --> 00:01:36,440 We cover the installation of python and adding this terminal to Adam there. 29 00:01:36,800 --> 00:01:37,220 OK. 30 00:01:37,340 --> 00:01:41,770 So make sure you're in the same location right here at your command line as you originally were. 31 00:01:41,780 --> 00:01:47,210 When you say the file so under-class examples my file is there in order to run this all I need to do 32 00:01:47,390 --> 00:01:51,600 is say Python space and then the name of the file. 33 00:01:51,650 --> 00:01:57,720 In my case it's called My example the PI I hit enter and now as the output I should see whatever it 34 00:01:57,720 --> 00:01:58,400 was printing. 35 00:01:58,490 --> 00:01:59,430 Hello world. 36 00:01:59,460 --> 00:01:59,910 OK. 37 00:02:00,020 --> 00:02:00,730 Perfect. 38 00:02:00,740 --> 00:02:05,210 If you have any issues again not seeing this little plus button in the lower left hand corner or maybe 39 00:02:05,210 --> 00:02:09,830 you haven't set up python yet go back to the very beginning check up our installation and setup lecture. 40 00:02:09,830 --> 00:02:14,180 We cover all that stuff and we actually have a time set for you so you can head forward in that video 41 00:02:14,270 --> 00:02:15,100 and check it all out. 42 00:02:15,320 --> 00:02:15,780 OK. 43 00:02:15,950 --> 00:02:21,260 With that being said and it's discussed now it's just very basic Python essentially how to do very basic 44 00:02:21,260 --> 00:02:22,020 math. 45 00:02:22,460 --> 00:02:27,420 So for example if we ever want to do addition and for this I'm actually going to zoom in a lot more. 46 00:02:27,440 --> 00:02:28,130 There we go. 47 00:02:28,130 --> 00:02:31,060 And let me clear my screen. 48 00:02:31,250 --> 00:02:31,800 OK. 49 00:02:32,120 --> 00:02:36,590 So if I ever want to do math such as Ed. I can say two plus one. 50 00:02:36,650 --> 00:02:39,330 So if I run that I get back three. 51 00:02:39,500 --> 00:02:46,140 If you ever want to do division that's going to be one forward slash to if you save that and you were 52 00:02:46,150 --> 00:02:47,970 to run that you'd get back 0.5. 53 00:02:47,970 --> 00:02:51,700 Notice how this is now a floating point even though these two were integers. 54 00:02:51,930 --> 00:02:54,210 And then we can also do subtraction. 55 00:02:54,210 --> 00:02:57,060 So one minus two that should give us a negative one. 56 00:02:57,270 --> 00:03:01,710 And there it is negative 1 is the output multiplication is an asterix. 57 00:03:01,710 --> 00:03:04,640 So we can say it 1 times 3. 58 00:03:05,030 --> 00:03:06,580 Or let's say three times three. 59 00:03:06,660 --> 00:03:07,950 So it's more obvious. 60 00:03:08,010 --> 00:03:12,010 So we'll save that three times three and we get back 9 as a result. 61 00:03:12,030 --> 00:03:13,300 So it makes sense. 62 00:03:13,320 --> 00:03:17,850 Keep in mind that if I didn't have the print statement here and I just said three times three and I 63 00:03:17,850 --> 00:03:21,990 tried to run this it would have no problem running it you just wouldn't see the output. 64 00:03:21,990 --> 00:03:27,150 So again in order to see the output we should be printing things so Prince overprint sees whatever the 65 00:03:27,150 --> 00:03:30,930 thing is and then enclose princes division we already went over. 66 00:03:30,960 --> 00:03:35,400 If you ever want to do something to the power for instance if I want to do that power three it's just 67 00:03:35,400 --> 00:03:36,290 to Asterix in a row. 68 00:03:36,320 --> 00:03:41,580 So two to the power of three I save that I run that it's going to be two times two times two. 69 00:03:41,580 --> 00:03:43,110 So in that case it's eight. 70 00:03:43,500 --> 00:03:48,180 And the last thing I want to mention here is the order of operations actually followed by Python. 71 00:03:48,450 --> 00:03:50,110 So I get to do that through an example. 72 00:03:50,550 --> 00:03:56,810 I'll say two plus ten times ten plus three. 73 00:03:56,820 --> 00:04:02,010 So Python is going to follow your standard order of operations which means multiplication here is going 74 00:04:02,010 --> 00:04:04,460 to happen first before this addition. 75 00:04:04,500 --> 00:04:08,750 So when I run this it's going to say OK ten times ten is one hundred. 76 00:04:08,760 --> 00:04:10,080 And then it's going to add them all up. 77 00:04:10,080 --> 00:04:13,550 So two plus 100 plus three which is 1 0 5. 78 00:04:13,740 --> 00:04:14,390 But let's imagine. 79 00:04:14,400 --> 00:04:19,340 I want to add this number first and then add these two numbers first and then multiply that result. 80 00:04:19,560 --> 00:04:25,800 Well I use parentheses to actually dictate the order of operations I want so I can wrap these in parentheses 81 00:04:26,190 --> 00:04:27,810 just like you would for normal math. 82 00:04:28,140 --> 00:04:32,550 Let's wrap these guys in princes and then we were going to add one more set of princes because that's 83 00:04:32,610 --> 00:04:34,480 outside that a prince is for Prince. 84 00:04:34,530 --> 00:04:39,780 So now I'm going to say OK add two plus 10 first then add templates 3 and then multiply these guys for 85 00:04:39,780 --> 00:04:40,800 the result. 86 00:04:40,800 --> 00:04:44,800 So I say run it and I get back 156 this time. 87 00:04:44,970 --> 00:04:45,220 OK. 88 00:04:45,240 --> 00:04:47,050 That should have been a very straight for and pretty basic. 89 00:04:47,080 --> 00:04:49,500 It's just how to do basic arithmetic with python. 90 00:04:49,500 --> 00:04:51,390 A lot of it been pretty intuitive. 91 00:04:51,390 --> 00:04:53,380 Now let's talk about variable assignments. 92 00:04:53,550 --> 00:04:57,660 OK let's take a quick dive into variable assignments in Python. 93 00:04:57,660 --> 00:05:01,770 So we just saw how to work with numbers but often we're asking ourselves well what do these numbers 94 00:05:01,770 --> 00:05:02,880 actually represent. 95 00:05:02,880 --> 00:05:08,160 I'm just writing two or three will to of one or three of what is actually a pretty nice if I could assign 96 00:05:08,160 --> 00:05:12,930 these data types a variable name that I can easily reference them later on in our code. 97 00:05:13,170 --> 00:05:18,150 For example instead of just having to I could say the variable my underscore dogs is equal to two. 98 00:05:18,270 --> 00:05:19,820 And then I could reference that variable name. 99 00:05:19,860 --> 00:05:26,680 My dogs throughout my script now there are a couple of rules for choosing a variable name variable names 100 00:05:26,680 --> 00:05:28,420 that cannot start a number. 101 00:05:28,420 --> 00:05:30,250 There can also be no spaces in the name. 102 00:05:30,250 --> 00:05:35,290 Instead you should use an underscore and you can't use any of these special symbols such as an exclamation 103 00:05:35,290 --> 00:05:37,320 mark or question mark or a dollar sign. 104 00:05:37,330 --> 00:05:38,760 So none of those symbols are allowed. 105 00:05:38,800 --> 00:05:43,480 Essentially you just be using lower case letters and then underscore and you can also use numbers as 106 00:05:43,480 --> 00:05:49,170 long as they're not the first letter or character in the variable name. 107 00:05:49,170 --> 00:05:53,170 Now there's also best practices for variable names and this is known as pep 8. 108 00:05:53,340 --> 00:05:57,110 So in general it's considered best practice that the names are all lowercase. 109 00:05:57,210 --> 00:05:59,410 It'll still work even if they're not lowercase. 110 00:05:59,430 --> 00:06:02,910 It's just a convention so that when you're reading someone else's code or someone else is reading your 111 00:06:02,910 --> 00:06:06,790 code it follows the same sort of basic convention or best practice. 112 00:06:06,810 --> 00:06:12,270 You should also avoid using words that have a special meaning in Python such as list or as TR. 113 00:06:12,270 --> 00:06:17,280 Often there are built in variables that are already used within Python and will be going through them 114 00:06:17,310 --> 00:06:21,850 throughout the course but a very common on that beginners often mistake is using list. 115 00:06:21,870 --> 00:06:27,430 So don't use that as a variable name because it's actually already built into Python. 116 00:06:27,540 --> 00:06:31,410 The last thing I want to mention is that Python actually uses dynamic typing. 117 00:06:31,410 --> 00:06:36,390 This means you can reassign variables to different data types and this makes Python very flexible in 118 00:06:36,390 --> 00:06:41,370 assigning data types and it's actually different than other languages that are what is known as statically 119 00:06:41,370 --> 00:06:42,110 typed. 120 00:06:42,120 --> 00:06:47,100 So let me quickly show you the difference between statically typed and dynamic typed. 121 00:06:47,440 --> 00:06:53,020 So let's imagine somewhere in my Python script maybe at the top I say my underscore dogs is equal to 122 00:06:53,020 --> 00:06:53,500 two. 123 00:06:53,530 --> 00:06:58,180 And then there's a bunch of code and then later at the end I say all right same variable name my underscore 124 00:06:58,180 --> 00:07:02,740 dog is not equal to what is known as a list of Samie and Franki. 125 00:07:02,740 --> 00:07:06,790 Python isn't going to complain that you suddenly change an integer into a list. 126 00:07:06,820 --> 00:07:08,450 That's totally OK in Python. 127 00:07:08,530 --> 00:07:11,910 You don't have to specify beforehand what my dogs was going to be. 128 00:07:11,920 --> 00:07:14,820 You'd have to say OK this is going to be integer or this is going to be a list. 129 00:07:14,980 --> 00:07:17,600 That's not always the case in other programming languages. 130 00:07:17,620 --> 00:07:20,190 So this is known as they Nemec typing in Python. 131 00:07:20,200 --> 00:07:24,940 It makes it really easy to code things really fast but it also leaves the potential for mistakes to 132 00:07:24,940 --> 00:07:25,330 be done. 133 00:07:25,360 --> 00:07:27,700 So just keep that in mind there is a tradeoff here. 134 00:07:28,740 --> 00:07:31,340 So again that can produce an error in other languages. 135 00:07:31,590 --> 00:07:37,030 So something that was statically typed for example to C++ you'd have to add the clear first integer. 136 00:07:37,050 --> 00:07:39,260 My dog is equal to one semi-colon. 137 00:07:39,390 --> 00:07:43,940 And then if you try to reassign my dog to something that wasn't an integer that would result in an error. 138 00:07:43,950 --> 00:07:45,770 So that's called static typing. 139 00:07:45,780 --> 00:07:50,760 However again Python doesn't use static typing Toney's dynamic typing which is why it's so popular for 140 00:07:50,760 --> 00:07:53,480 beginners and it's easy to learn. 141 00:07:53,510 --> 00:07:57,980 So again the pros of dynamic typing it's very easy to work with has faster development time. 142 00:07:57,980 --> 00:07:59,660 The cons of dynamic typing. 143 00:07:59,660 --> 00:08:02,000 It may result in bugs for unexpected data types. 144 00:08:02,010 --> 00:08:03,420 They need to be aware of that type. 145 00:08:03,470 --> 00:08:07,720 All you need to do is use that builtin type function which will go over in future lectures. 146 00:08:07,890 --> 00:08:13,550 OK so let's get an idea of all of this together by jumping over back to the Adam text editor and going 147 00:08:13,550 --> 00:08:15,620 through a couple of more examples. 148 00:08:15,620 --> 00:08:17,820 Ok here I am again at my example that PI. 149 00:08:17,870 --> 00:08:23,880 I'm going to delete this print statement save that change and when to clear out my terminal here. 150 00:08:24,290 --> 00:08:26,800 OK so the first thing going to do is just do an assignment. 151 00:08:26,810 --> 00:08:32,770 So say a is equal to the number 10 and then I can print out a. 152 00:08:32,800 --> 00:08:34,820 Let's save that. 153 00:08:35,000 --> 00:08:38,090 And when I run this I get back 10. 154 00:08:38,160 --> 00:08:39,340 So now I have high. 155 00:08:39,390 --> 00:08:42,590 I've assigned the variable a to the number 10. 156 00:08:42,630 --> 00:08:45,590 Now it's really interesting as I can actually use a to read the fine. 157 00:08:45,900 --> 00:08:52,050 So then later on in my code what I could say is OK now am going to be equal to a plus a. 158 00:08:52,140 --> 00:08:53,310 So what does that actually mean. 159 00:08:53,310 --> 00:08:57,850 It means a starts off as 10 and then you're going to reassign it to be equal to a plus a. 160 00:08:57,900 --> 00:09:03,480 So then you would expect when you print out a after that to get 20 because 10 plus 10 is 20 which is 161 00:09:03,480 --> 00:09:05,090 what happened exactly when and run it. 162 00:09:05,100 --> 00:09:07,370 Now you get back 20 as the output. 163 00:09:07,800 --> 00:09:11,820 OK let's show you a more realistic example because you won't just be using variable names like this. 164 00:09:11,820 --> 00:09:16,720 Let's imagine that we just had a bunch of puppies born so let's say six puppies were born. 165 00:09:17,500 --> 00:09:19,270 So we'll say puppies is equal to six. 166 00:09:19,340 --> 00:09:24,260 And each of them weighs two pounds which I'm actually not sure if that's a lot or a little for a puppy 167 00:09:24,290 --> 00:09:26,500 but hopefully bear with me here. 168 00:09:26,720 --> 00:09:28,370 So two pounds per puppy. 169 00:09:28,370 --> 00:09:31,300 Now the question is what's the total weight of all the puppies. 170 00:09:31,520 --> 00:09:36,000 Well now I can use variable names to easily find this in a very readable way. 171 00:09:36,080 --> 00:09:45,040 I'll just say something like total Ezekial to puppies times and then I'll just print out the totals 172 00:09:45,260 --> 00:09:47,670 to report that. 173 00:09:47,730 --> 00:09:48,750 So say that again. 174 00:09:48,750 --> 00:09:52,710 All I'm doing here is variable assignments and then I'm working the variables of the same arithmetic 175 00:09:52,770 --> 00:09:55,190 I was working with numbers when I run this. 176 00:09:55,230 --> 00:09:58,510 Now I get back the result six times two which is 12. 177 00:09:58,530 --> 00:10:00,610 So now my total is assigned to 12. 178 00:10:00,630 --> 00:10:01,160 OK. 179 00:10:01,290 --> 00:10:06,030 So we just learned some of the basics of numbers and arithmetic and also how we can create what are 180 00:10:06,030 --> 00:10:10,490 essentially labels for all these data types through the use of variable assignments. 181 00:10:10,500 --> 00:10:14,430 Hopefully this was pretty intuitive and pretty straightforward but if you have any questions feel free 182 00:10:14,430 --> 00:10:15,990 to post the Q&A forums. 183 00:10:15,990 --> 00:10:17,010 We'll see you at the next lecture.