Would you like to inspect the original subtitles? These are the user uploaded subtitles that are being translated: 1 00:00:00,469 --> 00:00:07,770 Great, now let's learn numbers. Let me open an interactive shell here to 3 00:00:07,770 --> 00:00:13,380 explain this faster and so numbers, you know what numbers are. To create a number 5 00:00:13,380 --> 00:00:19,640 just type the number in python and that's it and you also have operators 7 00:00:19,640 --> 00:00:25,350 like this is the plus operator and you can also store numbers in variables 9 00:00:25,350 --> 00:00:33,020 let's say a equals to 2, b equals to 3 and then if you do a plus b you get 5. 11 00:00:33,020 --> 00:00:41,550 Something to note is that you know if you do that in here, a equals to 2 b 13 00:00:41,550 --> 00:00:48,170 equals to 3, and then if you just do a plus B and then you execute the script, 15 00:00:48,170 --> 00:00:58,739 let me open another terminal, you will not get any output in there. The reason 17 00:00:58,739 --> 00:01:04,559 is that you are not printing out anything in your program, so this is 19 00:01:04,559 --> 00:01:10,229 different from an interactive session. Here if you simply do an operation or if 21 00:01:10,229 --> 00:01:16,650 you simply call a variable like that, you'll get the output promptly, so this is just 23 00:01:16,650 --> 00:01:21,840 for simplicity when you when you try things out, so you don't have to pass 25 00:01:21,840 --> 00:01:27,600 print explicitly, but Python will understand that you met print. But here 27 00:01:27,600 --> 00:01:35,130 things are more strict, so you if you want to print out the output, you want 29 00:01:35,130 --> 00:01:43,680 to say print a plus b and then execute and you get the output and yeah basically 31 00:01:43,680 --> 00:01:48,960 that's the only difference between executing a program from a Python file 33 00:01:48,960 --> 00:01:56,130 and running the code in the interactive shell, so these are numbers and I can 35 00:01:56,130 --> 00:02:03,439 prove that if I do type 2 for instance. You'll see that this is an INT 37 00:02:03,439 --> 00:02:10,289 type which means is an integer, so basically we have integers and we have 39 00:02:10,289 --> 00:02:13,799 floats. These are the two main types of numbers. 41 00:02:13,799 --> 00:02:22,379 A float is, let's say 2.4 it's a float and I can prove that 2.4, 43 00:02:22,379 --> 00:02:30,359 type 2.4. You'll see that this is a float, however if you do type 2 in 45 00:02:30,359 --> 00:02:35,609 brackets you'll see that this is a string, it's not a number and therefore 47 00:02:35,609 --> 00:02:42,689 you cannot make operations using a string and a number so Python will give 49 00:02:42,689 --> 00:02:47,430 you a type error and this is saying cannot convert integer to string 51 00:02:47,430 --> 00:02:54,569 implicitly so when you do a string plus something else Python expects that you 53 00:02:54,569 --> 00:03:00,000 were adding another string after a plus sign, so that's why it says I cannot 55 00:03:00,000 --> 00:03:05,549 convert integer object, so it cannot convert this to a string implicitly 57 00:03:05,549 --> 00:03:14,040 because if you were to do two plus three you'd get 23 because Python treats these 59 00:03:14,040 --> 00:03:17,189 two as text. So to understand it better 61 00:03:17,189 --> 00:03:26,729 let's add some text here b so you get 2a3b, so it's a concatenation operation. 63 00:03:26,729 --> 00:03:31,199 When the plus operator is used with strings it is referred to as 65 00:03:31,199 --> 00:03:37,010 concatenation. Now let's go back to our sample program that we used earlier 67 00:03:37,010 --> 00:03:44,549 which was this one in here, so now what if instead of getting a greeting from 69 00:03:44,549 --> 00:03:53,220 the user you ask their for their age? Enter your age, so this is just a message 71 00:03:53,220 --> 00:03:56,879 you can write anything you want there, but just try to have a message that 73 00:03:56,879 --> 00:04:04,680 makes some sense to the user and so also I'm going to change the variable name to 75 00:04:04,680 --> 00:04:11,400 something more meaningful, age and then what I want to do is let's say new age, 77 00:04:11,400 --> 00:04:18,790 I want to calculate the age plus 50. Why not? 79 00:04:18,790 --> 00:04:28,540 I'll print out the new age. Save the script and let's go and execute this, we are 81 00:04:28,540 --> 00:04:33,130 going to get an error here I warn you. But it's good that you see the errors 83 00:04:33,130 --> 00:04:36,030 that you get because that's how you learn better. 85 00:04:36,030 --> 00:04:45,580 So Python my program, execute. For now it's working fine because what 87 00:04:45,580 --> 00:04:51,280 happens is Python executes a script line by line so it goes to the first 89 00:04:51,280 --> 00:04:56,980 line and if there is no error it executes that line and in this case we have 91 00:04:56,980 --> 00:05:02,830 an input function so the program is on standby mode so it expects from the user 93 00:05:02,830 --> 00:05:10,780 to enter the input, so let's enter the input here. Let's say 28 and here is the 95 00:05:10,780 --> 00:05:16,420 error that we get. So again we saw this error before. This is saying type error 97 00:05:16,420 --> 00:05:21,250 cannot convert int object to string implicitly and you also have the line 99 00:05:21,250 --> 00:05:30,630 here that the error occurred. So these are important messages and line two in here. 101 00:05:30,630 --> 00:05:37,270 So what's happening is that age is a string it's not a number therefore 103 00:05:37,270 --> 00:05:43,180 python cannot add up a string with a number and so why is age a string? 105 00:05:43,180 --> 00:05:48,520 Because that's what the input function produces, so the input function get the 107 00:05:48,520 --> 00:05:55,000 user input and converts it to a string so even if you pass a number there these 109 00:05:55,000 --> 00:05:59,140 will always convert everything to a string. 111 00:05:59,140 --> 00:06:07,570 Therefore Python you know cannot concatenate 28 plus 50 so what can you 113 00:06:07,570 --> 00:06:13,480 do in that case? Well you want to convert that string into an integer and for 115 00:06:13,480 --> 00:06:19,360 that you want to use the int function, so it's a Python function that does the work. 117 00:06:19,360 --> 00:06:27,570 As you can see it outputs now the correct output so 28 plus 50 equals 119 00:06:27,570 --> 00:06:32,410 78 and similarly you can convert numbers to strings 121 00:06:32,410 --> 00:06:42,280 and let's say str 50 and I think we'll get an error here. Yeah, it says type error. 123 00:06:42,280 --> 00:06:48,580 Unsupported operand type four plus. So you're adding up an integer with a 125 00:06:48,580 --> 00:06:57,850 string, so integer with a string. If you like to convert this to a float, let me 127 00:06:57,850 --> 00:07:07,270 remove that, save, execute. 28. You get 78 point zero because what 129 00:07:07,270 --> 00:07:19,330 Python does when you use float is you know float 28, it converts it to 28.0. 131 00:07:19,330 --> 00:07:24,160 So floats can be useful in certain scenarios. And you'll have a lot of scenarios in the 133 00:07:24,160 --> 00:07:28,690 course, so don't worry about that now because we have real world 135 00:07:28,690 --> 00:07:33,490 applications later on where you see the real benefit of everything that you are 137 00:07:33,490 --> 00:07:39,040 explaining here in this early sections that cover the basics. So this is about 139 00:07:39,040 --> 00:07:43,540 numbers. Try to practice them a little bit and I'll talk to you in the next 141 00:07:43,540 --> 00:07:45,690 lecture. 8316