WEBVTT 0 00:00.230 --> 00:07.730 In the previous challenge, you saw that when we calculated the BMI and we printed out this large number 1 00:07.730 --> 00:14.660 divided by another number, usually there is a large number of digits after the decimal place. 2 00:14.690 --> 00:21.230 Now, this is not really an ideal way to output some number to the user. 3 00:21.230 --> 00:28.760 We'd really like to be able to round it to the nearest whole number or to a specified number of digits. 4 00:28.760 --> 00:31.160 So how do we do this? 5 00:31.190 --> 00:37.790 Well, you've already seen that we can convert any number into an integer. 6 00:37.910 --> 00:44.510 So instead of simply just printing the original BMI, we can convert it first into an integer, 7 00:44.510 --> 00:46.670 and then we try printing it. 8 00:46.670 --> 00:51.050 You can see what this does is it floors the number. 9 00:51.050 --> 00:57.820 And this is a programming term for basically just removing all of the remaining decimal places, flooring 10 00:57.820 --> 01:00.850 it to the lowest whole number. 11 01:01.030 --> 01:03.160 Now that's not quite what we want. 12 01:03.160 --> 01:10.060 We want to use the round() function which performs the rounding in the traditional mathematical sense, 13 01:10.060 --> 01:16.360 where when it's 0.5, it rounds up to the next whole number, and when it's below that, it rounds up 14 01:16.360 --> 01:19.240 to the lower whole number. 15 01:19.240 --> 01:27.130 So let's go ahead and print using the round() function and round our BMI instead. 16 01:27.130 --> 01:29.410 See what all three of them print. 17 01:29.410 --> 01:33.970 So this is our original value 30.85, 18 01:33.970 --> 01:37.150 and when we simply chop off the end, 19 01:37.150 --> 01:39.850 we have a whole number 30. 20 01:39.850 --> 01:41.700 And this is called flooring. 21 01:41.700 --> 01:49.080 Whereas rounding we'll round up or down one whole number depending on the first decimal place. 22 01:49.080 --> 01:51.510 So in this case it becomes 31. 23 01:52.350 --> 02:04.650 So this depends on, of course, whether it is 3.9 will round into 4, whereas 3.3 will round into 3. 24 02:04.650 --> 02:11.400 So it's a really, really handy function when we're working with numbers in Python. 25 02:11.430 --> 02:16.950 Now you can go even one step further, instead of just rounding the number... 26 02:16.950 --> 02:20.040 notice that it actually takes two inputs. 27 02:20.040 --> 02:27.450 So when I typed out round, and you can see the auto-suggest showing me the function that it thinks I'm 28 02:27.450 --> 02:30.750 trying to get hold of, it takes two inputs. 29 02:30.750 --> 02:37.530 One is the number you want to round, and the second one is the number of digits you want to round it 30 02:37.530 --> 02:38.040 to, 31 02:38.040 --> 02:45.360 which is kind of helpful because what if we want to take our BMI and we wanted to round it to two decimal 32 02:45.360 --> 02:46.140 places? 33 02:46.140 --> 02:52.560 Well, then we would write bmi as the number that will be inserted here, from this variable, 34 02:52.560 --> 02:55.280 and then we just simply type 2. 35 02:55.280 --> 03:00.860 And now when I hit Run, you'll see that this time, instead of simply rounding it to a whole number, 36 03:00.860 --> 03:06.530 it rounds it to a floating point number with two decimal places of accuracy. 37 03:07.160 --> 03:08.780 So that can be really helpful 38 03:08.780 --> 03:15.800 if you're working with money, for example, and you're doing Pythonic calculations, working with currencies 39 03:15.800 --> 03:17.000 or conversions. 40 03:17.000 --> 03:21.020 So Python is just generally really, really number friendly. 41 03:21.410 --> 03:30.020 Now while we're working with numbers in Python, another really handy operator is called the Assignment 42 03:30.020 --> 03:31.160 Operator. 43 03:31.160 --> 03:36.230 So we have various different ones depending on which mathematical operation you want to do. 44 03:36.230 --> 03:43.720 But essentially, what this allows us to do is to accumulate the results of our calculations. 45 03:44.200 --> 03:50.470 Now, very often when you're writing code, say, for example, if you're keeping track of the user's 46 03:50.470 --> 03:51.370 score, 47 03:51.370 --> 03:54.640 so you could have score = 0 to begin with. 48 03:54.640 --> 04:01.960 And every single time in your code, say a user scores a point, then you can get hold of this score 49 04:01.960 --> 04:02.980 variable again, 50 04:02.980 --> 04:09.460 and instead of saying score now equals the previous value of score + 1, you can simply use this 51 04:09.460 --> 04:11.410 shorthand +=. 52 04:11.410 --> 04:13.180 So, +=1. 53 04:13.180 --> 04:18.820 And now when we print score you'll see that it's actually equal to 1. 54 04:19.570 --> 04:26.620 So instead of using += you can use -= which just takes the previous version of score 55 04:26.620 --> 04:28.660 and removes 1 from it, 56 04:28.690 --> 04:31.450 *=, and /=. 57 04:31.450 --> 04:37.360 So this is really handy when you have to manipulate a value based on its previous value, which you'll 58 04:37.360 --> 04:38.980 have to do a lot in programming. 59 04:39.580 --> 04:44.110 Now, the final thing I want to show you is something called f-Strings. 60 04:44.170 --> 04:49.930 And this makes it really easy to mix strings and different data types. 61 04:50.050 --> 04:59.730 So far, up to this point, if we wanted to print something like, "Your score is..." and then we wanted 62 04:59.730 --> 05:02.250 it to print the score, we have to write +, 63 05:02.250 --> 05:07.500 but of course, because these are different data types; this is a string and this is an integer, we 64 05:07.500 --> 05:08.580 get a TypeError. 65 05:08.670 --> 05:13.380 So we've had to convert this into a string before 66 05:13.380 --> 05:17.580 it will actually successfully print, when both the data types match. 67 05:17.730 --> 05:25.050 Now this is quite painful, and understandably, a lot of programmers will need some slightly more convenient 68 05:25.050 --> 05:28.740 way of incorporating things that have different data types. 69 05:28.740 --> 05:32.010 Let's say, the score = 0. 70 05:32.130 --> 05:39.390 Let's say their height = 1.8, and is_winning = True. 71 05:39.390 --> 05:46.190 So here we've got an integer, a float, and a boolean, and we want to mix it all in to a sentence that 72 05:46.190 --> 05:48.290 is a string and get it printed out. 73 05:48.290 --> 05:55.730 So instead of having to convert all of these and use a whole bunch of plus signs, and then you have 74 05:55.730 --> 06:00.650 to convert everything into a string, it's really, really painful, right? 75 06:00.650 --> 06:08.240 So what we can do instead is use something in Python known as an f-string. 76 06:08.990 --> 06:17.090 And what an f-string allows us to do is in front of a string like this one, we type the character f, 77 06:17.090 --> 06:21.440 and it's really important that it goes in front of the double quotes or single quotes, 78 06:21.440 --> 06:23.390 if you want to write your strings like this. 79 06:23.390 --> 06:27.770 But I like to use double quotes, and a lot of other Python programmers do too. 80 06:27.800 --> 06:33.450 So essentially you're adding just the character f in front of the string. 81 06:33.450 --> 06:35.580 And now this is an f-string. 82 06:35.580 --> 06:39.870 And you can start adding various values into this string. 83 06:39.870 --> 06:47.070 So for example if I wanted to write your score is equal to this variable score, then I can put that 84 06:47.070 --> 06:51.180 variable inside a set of curly braces { } like this. 85 06:51.300 --> 07:00.160 And now when I print my string, this one right here, you'll see that it says, "Your score = 0." 86 07:00.160 --> 07:04.090 And it does all of the converting and all of the stuff behind the scenes, 87 07:04.090 --> 07:06.370 and you don't have to worry about any of this. 88 07:06.700 --> 07:17.230 So if I want to continue along, I could say, "Your score is {score}, your height is..." add in the "{height}..." and 89 07:17.230 --> 07:22.150 then, "You are winning is..." 90 07:22.270 --> 07:29.350 Then let's add that final boolean value "{is_winning}" and get it to run. 91 07:29.350 --> 07:32.830 You can see that our entire string now prints out, "Your score is = 0, 92 07:32.860 --> 07:34.240 your height is 1.8. 93 07:34.240 --> 07:36.100 You are winning is True." 94 07:36.100 --> 07:42.910 So all of these different data types got combined into a string by using an f in front of the string, 95 07:42.910 --> 07:49.470 and then using these curly braces to place our variables into the string. 96 07:49.950 --> 07:57.450 By using f-strings, you cut down on a lot of the manual labor of inserting different data types into 97 07:57.450 --> 08:04.140 a string, and this is going to come in really handy just about on the next lesson where I've got a 98 08:04.140 --> 08:08.730 coding challenge for you. Head over there and complete the challenge.