WEBVTT 0 00:00.780 --> 00:04.830 In the last lesson, we managed to get our countdown mechanism to work, 1 00:05.160 --> 00:10.100 and we got it to count down from five minutes to zero. Now, everything works, 2 00:10.580 --> 00:14.510 but there's just something a little bit niggling and you'll see it when I hit 3 00:14.510 --> 00:18.200 start. Notice how it says 5:0. 4 00:18.740 --> 00:21.880 Wouldn't it be so much better if it said 5:00? 5 00:23.450 --> 00:25.280 So how would we do that? Well, 6 00:25.550 --> 00:30.320 that is the zero comes from this count_sec because it's taking the count in 7 00:30.320 --> 00:35.210 seconds, dividing it by 60 and finding the remainder using the modulo. 8 00:35.720 --> 00:39.140 Now, when there is no remainder, it's just going to be equal to zero. 9 00:39.620 --> 00:42.500 So we could use an if statement and check well 10 00:42.740 --> 00:45.800 if the count_sec is equal to zero, 11 00:46.190 --> 00:50.990 then instead of making it zero, let's set it to equal a string 12 00:51.020 --> 00:52.160 which is "00". 13 00:52.790 --> 00:56.150 Now this actually, believe it or not, works. 14 00:56.900 --> 00:58.310 And you'll see it when I run it. 15 00:58.340 --> 01:01.250 When I hit start, doesn't that look so much better? 16 01:02.330 --> 01:07.330 But some of you might've realized that there's something a little bit crazy going on 17 01:07.640 --> 01:09.380 here in these two lines of code. 18 01:09.830 --> 01:14.830 We're checking to see if this variable holds data that is equal to the integer, 19 01:16.610 --> 01:18.650 the whole number zero, 20 01:19.250 --> 01:21.890 and then we're setting it to a string. 21 01:22.310 --> 01:26.000 So these are completely two different data types. 22 01:26.030 --> 01:29.120 That's an int and that is a string. 23 01:29.540 --> 01:32.450 So how is it that we're able to do this? 24 01:33.350 --> 01:36.350 So let me pull up the Python console. 25 01:36.560 --> 01:39.260 We know that if we took a integer, 26 01:39.290 --> 01:44.180 say 3, and we try to add it to a string, say a 4, 27 01:44.480 --> 01:45.800 this is not going to work 28 01:45.830 --> 01:50.330 and we get a type error because this is type int 29 01:50.420 --> 01:52.250 and this is type string. 30 01:52.520 --> 01:57.520 So you can't actually add these two together because there's a mismatch. 31 01:58.250 --> 01:59.720 Now here's the crazy thing. 32 01:59.840 --> 02:04.550 Let's create a variable a and let's make it hold the integer with 3. 33 02:05.150 --> 02:10.150 And at this point, you can see that this a variable has a data type of int. 34 02:11.390 --> 02:16.130 If I decide to change that variable and make it hold a different type of data, 35 02:16.430 --> 02:19.400 let's say the number 4, or let's make it simpler, 36 02:19.400 --> 02:23.870 let's make it hold the piece of text, Hello. As soon as that goes through, 37 02:23.870 --> 02:27.410 you can see that a is now of data type string. 38 02:28.010 --> 02:30.950 And the very fact that I'm able to do that, 39 02:31.100 --> 02:36.100 change a variable's data type by changing the content in that variable, 40 02:37.310 --> 02:42.310 this is what's known as dynamic typing. In this sense, 41 02:42.770 --> 02:47.770 Python is a language that's quite unique because on one hand it is strongly 42 02:48.380 --> 02:53.380 typed, in the sense that it holds on to the data type of the variable, 43 02:54.230 --> 02:58.670 so this a is a string and it knows that it's a string 44 02:59.110 --> 03:02.650 and if you do something that is not meant for a string, 45 03:03.010 --> 03:06.640 say if you try to raise a to the power of 2, 46 03:07.090 --> 03:11.440 then that is going to be a type error. Types matter 47 03:11.800 --> 03:15.280 and when you call a function that's expecting a particular type, 48 03:15.610 --> 03:18.070 say if you use the power function 49 03:18.100 --> 03:22.600 which is expecting a integer and you pass in something 50 03:22.630 --> 03:26.980 that's obviously not an integer say, our string here 51 03:27.700 --> 03:32.020 and you try to get it to do some things, say raise it to the power of 3, 52 03:32.380 --> 03:34.300 then again, we get type error. 53 03:34.330 --> 03:37.510 It knows what type is supposed to go into that function 54 03:37.840 --> 03:40.570 and it makes sure that you comply with that. 55 03:40.600 --> 03:43.150 This is where the language is strongly typed. 56 03:43.660 --> 03:48.660 But the part where the language is dynamically typed is that even though it 57 03:48.700 --> 03:51.160 knows what type a variable is, 58 03:51.220 --> 03:54.100 it knows what type a function expects, 59 03:54.580 --> 03:59.580 you can also dynamically change the data type of any variable like this. 60 04:02.500 --> 04:06.130 That is basically what we're using here. We're using dynamic 61 04:06.130 --> 04:07.510 typing to change 62 04:07.510 --> 04:12.510 the data type of count_sec from a integer to a string. 63 04:13.210 --> 04:18.210 And then we use that string to display inside this canvas text. 64 04:19.390 --> 04:20.530 Now there is however, 65 04:20.530 --> 04:25.530 still a bit of a bug with this and you'll see it once it dips below 10 seconds. 66 04:27.430 --> 04:30.430 Notice that as soon as it goes to 9 seconds, 67 04:30.820 --> 04:34.660 instead of saying 09, which is what you would want or 08, 68 04:34.690 --> 04:35.523 06, 69 04:35.740 --> 04:40.740 it just lists the number of seconds until it reaches 00. 70 04:41.380 --> 04:43.690 So how can we fix this? 71 04:44.770 --> 04:47.050 The key lies in these two lines of code. 72 04:47.740 --> 04:49.810 See if you can do this as a challenge, 73 04:50.290 --> 04:55.290 pause the video and see if you can make it so that when it's nine seconds 74 04:55.390 --> 04:56.200 remaining, 75 04:56.200 --> 05:01.200 it says 09 or 08 or 07 and also 00 of course. 76 05:03.370 --> 05:07.840 Pause the video and see if you can complete this challenge. All right. 77 05:07.840 --> 05:12.700 So basically what we want to check for is when the count in seconds is less 78 05:12.700 --> 05:17.050 than 10, because now it's going to be in the single digits 79 05:17.230 --> 05:20.590 and instead of having just one digit, 80 05:20.650 --> 05:22.870 we wanna add a zero in front of it. 81 05:23.470 --> 05:26.890 So the way we can do this is through just an f-string. 82 05:27.340 --> 05:32.340 We can use an f-string to add the zero in front and then add the count in 83 05:32.620 --> 05:34.390 seconds afterwards, 84 05:34.600 --> 05:39.220 formatting that into the standard kind of time format. 85 05:40.270 --> 05:44.290 Now that we fixed that if we run our app again 86 05:44.590 --> 05:46.450 it goes down to 10 seconds 87 05:47.140 --> 05:51.190 you can see it now says 09, 08, 07 88 05:51.460 --> 05:54.430 and it's nicely formatted using our f-string. 89 05:55.660 --> 06:00.660 And we're able to do because of the flexibility of the data types in Python, 90 06:01.130 --> 06:02.480 checking it as a number, 91 06:02.510 --> 06:07.430 making sure it's less than 10 and then formatting it as a string and using the 92 06:07.430 --> 06:08.263 f-string. 93 06:08.900 --> 06:13.070 Now, this is not a feature that's available in all programming languages. 94 06:13.370 --> 06:17.090 For example, languages like C or Java or Swift, 95 06:17.420 --> 06:19.280 you won't be able to do this. 96 06:19.880 --> 06:24.470 Once you create a variable and you give it a certain type of data, 97 06:24.680 --> 06:27.830 then it must forever hold on to that type of data. 98 06:28.520 --> 06:33.520 But Python allows you to change the data type of a variable just by assigning it 99 06:34.820 --> 06:36.980 to a different type of value. 100 06:37.970 --> 06:42.800 There's a really well-worded Stack Overflow answer that addresses this exact 101 06:42.800 --> 06:43.040 thing 102 06:43.040 --> 06:47.870 I'm talking about, talking about the fact that Python is a strongly dynamically 103 06:47.870 --> 06:52.220 typed language. And I recommend that if you want to dig more into this, 104 06:52.370 --> 06:56.870 to have a read of this answer and I'll link to this in the course resources.