WEBVTT 0 00:00.480 --> 00:03.330 In the last lesson we saw how the asterix operator 1 00:03.330 --> 00:07.320 could be used to provide any number of positional arguments to a function 2 00:07.680 --> 00:11.370 because it collected them into a tuple. In this lesson, 3 00:11.430 --> 00:14.130 we'll take a look at the double asterix operator, 4 00:14.430 --> 00:18.750 and this is going to allow us to work with an arbitrary number of keyword 5 00:18.750 --> 00:20.940 arguments. Let's see this in action. 6 00:21.600 --> 00:24.360 So let's say I create another function called calculate, 7 00:24.720 --> 00:29.160 and this time I'm going to add two asteriks. And in this case, 8 00:29.220 --> 00:34.220 I'm going to call my argument **kwargs or keyword arguments. 9 00:34.770 --> 00:39.770 What we've done now is we've added two asterisks signs in front of this parameter 10 00:39.900 --> 00:40.733 name, 11 00:41.160 --> 00:45.630 and we've now created unlimited keyword arguments. 12 00:46.080 --> 00:51.080 What this allows me to do is I could basically now call this calculate function, 13 00:52.380 --> 00:57.090 I could pass in a keyword argument, for example, 14 00:57.210 --> 01:00.210 add, and let's give it a value, maybe three, 15 01:00.510 --> 01:04.740 and then let's add another keyword argument which I'll call multiply, 16 01:05.070 --> 01:08.910 set that to equal five. And effectively 17 01:08.940 --> 01:13.140 what this has been turned into is these **kwargs, 18 01:13.500 --> 01:18.210 which is basically a dictionary. So if I print these **kwargs, 19 01:18.810 --> 01:23.040 you can see what gets printed is basically a bog-standard dictionary. 20 01:23.490 --> 01:26.790 And in fact, if we do that type check thing again, so type, 21 01:28.620 --> 01:30.900 you can see it is in fact, a dictionary. 22 01:31.920 --> 01:36.810 This dictionary basically represents each of the keyword arguments and their 23 01:36.810 --> 01:37.643 values. 24 01:37.950 --> 01:42.570 So add is now a key and three is now it's value, multiply's 25 01:42.570 --> 01:45.660 the second key and five is its value. 26 01:46.140 --> 01:50.760 What I can do here is I could do the standard way of looping through dictionary. 27 01:50.760 --> 01:55.760 So I could say for key, value in **kwargs .items, 28 01:57.960 --> 02:02.160 and then I can get access to each of the keys and their values as I loop through 29 02:02.160 --> 02:04.800 the dictionary like this. 30 02:04.920 --> 02:08.910 So add three multiplied by five. Alternatively, 31 02:08.970 --> 02:11.700 I can simply use the names of the keys. 32 02:12.120 --> 02:17.120 So I could just simply print my **kwargs and then use the square brackets and then 33 02:18.270 --> 02:22.200 provide the name of the key, so add for example. 34 02:22.950 --> 02:27.060 And that will give me the value which is three as you can see here. 35 02:27.930 --> 02:28.260 Now, 36 02:28.260 --> 02:33.260 what this allows me to do is it basically lets me look through all of the inputs 37 02:34.920 --> 02:39.060 and find the ones that I want and use them to do something. 38 02:39.540 --> 02:44.100 So for example, in this case, it's a calculate function, right? 39 02:44.490 --> 02:48.420 So we could let's say start off with a normal positional argument, 40 02:48.450 --> 02:53.370 so let's call it n and let's pass in that n at the very beginning. 41 02:53.670 --> 02:58.500 So let's say we start out with the number 2, n is now equal to 2, 42 02:58.900 --> 03:03.700 and then the **kwargs is a dictionary of the remainder arguments. 43 03:05.290 --> 03:08.020 Let's say that I wanted to do some calculations. 44 03:08.050 --> 03:13.050 I wanted to say n+= kwargs, 45 03:13.870 --> 03:18.340 and I'm going to get hold of the value under add. 46 03:19.030 --> 03:22.960 And then I'm going to say, n*= the kwargs, 47 03:23.380 --> 03:26.290 and I'm going to get hold of value of multiply. 48 03:26.950 --> 03:30.250 So now when I go ahead and print 49 03:30.310 --> 03:35.310 my n, you can see that what happens is it takes the first value 2 as equal to n, 50 03:39.850 --> 03:44.380 and then n, this 2, is going to be added to the number I wanted to add 51 03:44.410 --> 03:46.660 which is 3. So 2 + 3 is 5, 52 03:47.140 --> 03:52.140 and then it multiplied that 5 by whatever it is I had stored in multiply. 53 03:52.660 --> 03:55.120 So 5 plus 5, and we get 25. 54 03:55.810 --> 04:00.460 This gives us a more flexible way of working with these arguments. 55 04:00.910 --> 04:05.500 And it gives us a way to name the values that we're passing in to this function. 56 04:06.880 --> 04:11.110 Now, coming back to what they've done in the Tkinter module, 57 04:11.650 --> 04:16.650 basically this Tkinter module is actually ported from another technology called 58 04:17.560 --> 04:18.393 TK. 59 04:18.940 --> 04:23.320 And TK actually has a very different syntax from Python. 60 04:23.950 --> 04:28.900 In order for it to work, they basically took all of the Tk commands, 61 04:28.930 --> 04:32.470 like creating a label or packing some sort of item, 62 04:32.920 --> 04:37.920 and took all of the options and turn them into these **kwargs or optional keyword 63 04:40.180 --> 04:41.013 arguments. 64 04:41.380 --> 04:46.000 And that is why when we create a new label from the Tkinter module 65 04:46.030 --> 04:48.310 or when we call the pack method, 66 04:48.520 --> 04:53.290 you can see that it doesn't actually come up with any properties that we can 67 04:53.290 --> 04:57.850 modify other than this **kw, 68 04:58.120 --> 05:00.580 which is the same as our **kwargs. 69 05:01.390 --> 05:04.390 So we could actually create a class like that as well, 70 05:04.660 --> 05:07.180 because this is done at initialization, right? 71 05:07.180 --> 05:09.640 This is done when they're creating that label class. 72 05:10.420 --> 05:13.810 Let's say that we create a class like this which I'll car, 73 05:14.410 --> 05:16.270 and in the init, 74 05:16.780 --> 05:21.430 what I'll include in addition to self is ** 75 05:21.670 --> 05:25.030 kw, or **kwargs, or however you want to spell it. 76 05:25.840 --> 05:30.840 This kw are going to be all of the optional arguments that I'll pass in 77 05:31.270 --> 05:35.950 when I'm initializing a new object from this class. I can say, 78 05:35.950 --> 05:38.770 for example, self. 79 05:38.830 --> 05:42.370 make of the car equals kw. 80 05:43.270 --> 05:47.230 And then from kw, I'm going to get the make. 81 05:48.010 --> 05:49.810 And then I'm going to have self.model 82 05:49.810 --> 05:53.980 which is going to be equal to kw and then model. And of course, 83 05:53.980 --> 05:57.830 all of the spelling matters so make sure you don't make any typos. 84 05:58.280 --> 06:00.260 And then I decide to create my car 85 06:00.290 --> 06:04.490 which is going to be the object created from this class. Now notice how 86 06:04.490 --> 06:06.440 when I open up the parentheses here, 87 06:06.740 --> 06:10.850 you don't actually see any of the properties like make and model show up 88 06:10.880 --> 06:14.480 when I'm initializing. All you see is ** 89 06:14.510 --> 06:18.380 kw, just in the same way as you see it here, 90 06:19.850 --> 06:21.680 **kw. 91 06:22.640 --> 06:26.750 And that of course refers to our optional keyword arguments. 92 06:27.320 --> 06:31.610 Let's add some values. Let's set the make to a Nissan, 93 06:32.150 --> 06:37.150 and lets set the model to a-- let's set it to a GT-R. And now I can use my object 94 06:40.820 --> 06:44.930 just as I would any other object. I can say my_car.model. 95 06:45.290 --> 06:49.580 And when I hit run, you can see I've got GT-R being printed here. 96 06:50.690 --> 06:54.740 And if I decided to print make, you can see 97 06:54.740 --> 06:55.970 it gets hold off the make. 98 06:56.480 --> 07:00.830 Now, what if I didn't actually specify one of these arguments. 99 07:01.430 --> 07:05.390 Notice how it's now actually going to crash. 100 07:06.020 --> 07:08.570 It tells me that keyError model. 101 07:08.750 --> 07:13.750 So when it was initializing this car object, it fell on this line. And it 102 07:15.800 --> 07:20.800 couldn't get hold of a value called model from this kw argument dictionary. 103 07:23.060 --> 07:24.650 In fact, with dictionaries, 104 07:25.040 --> 07:28.370 we can get hold of the values through the square bracket method, 105 07:28.640 --> 07:33.640 but we can also use a function called get. And we use get in a very similar way 106 07:35.030 --> 07:37.220 to the way that we use the square brackets. 107 07:37.250 --> 07:41.540 We just pass in the name of the key and we want to get hold of the value. 108 07:42.140 --> 07:47.140 But the benefit of get is that if this key doesn't exist in the dictionary, 109 07:50.510 --> 07:54.650 then it will just return none and it won't give us an error. 110 07:55.820 --> 08:00.080 So now if I run this code again, you can see that everything works, 111 08:00.320 --> 08:03.890 but my car.model is now equal to none. 112 08:04.580 --> 08:09.580 So this is how we can actually create a class with lots of optional keyword 113 08:10.340 --> 08:11.173 arguments. 114 08:12.110 --> 08:17.110 So we could have a self.color or self.seats. 115 08:21.050 --> 08:25.580 And depending on what it is we want to initialize this car object to, 116 08:25.910 --> 08:30.910 then we can simply go ahead and add whatever it is we want to set as the make 117 08:31.820 --> 08:35.750 and the model or the color and the seats. And in the same way 118 08:35.780 --> 08:38.060 that way using this label class, 119 08:38.390 --> 08:41.150 we can set the text or we can set the font. 120 08:41.270 --> 08:46.270 We can set all of the options or we can leave them as the default values. That 121 08:48.230 --> 08:52.610 should help you understand how this code works a little bit better. 122 08:53.180 --> 08:56.580 And the reason why it works like this is, as I say, 123 08:56.580 --> 09:01.580 mostly because this module was converted from another language and this just 124 09:01.950 --> 09:06.950 happened to be the most efficient way for them to do this. Now with other more 125 09:07.380 --> 09:11.280 Pythonic modules or things that have been created in Python 126 09:11.610 --> 09:16.260 like the turtle module, then you'll see more bog-standard kind of code 127 09:16.320 --> 09:19.740 like what we've been working with. So when we initialize a new turtle, 128 09:19.950 --> 09:22.530 you can see that it has a default shape, 129 09:22.620 --> 09:25.230 it has a visible boolean, 130 09:25.290 --> 09:29.190 and we can set all of those properties that we can see in this prompt. 131 09:30.510 --> 09:31.860 Now in the next lesson, 132 09:31.890 --> 09:36.210 I want to dive deeper into the TKinter documentation 133 09:36.570 --> 09:40.230 and I want to show you how we can create other components, not just the label, 134 09:40.470 --> 09:42.990 but things like buttons and text inputs 135 09:43.280 --> 09:46.790 and a whole range of things that will bring our GUI program to life. 136 09:47.210 --> 09:50.120 So for all of that and more, I'll see you in the next lesson.