WEBVTT 00:01.500 --> 00:06.330 Hello and welcome back to part two of our user defined function session. 00:06.330 --> 00:13.270 So far we only have one parameter in our functions but of course functions can also have many parameters. 00:13.350 --> 00:18.500 So let's define the function power very calculate x to the power of y 00:22.450 --> 00:24.660 so you know the function definition within the brackets. 00:24.670 --> 00:32.070 We have the parameters X and Y and we return x to the power of y and then we can call the function by 00:32.080 --> 00:35.210 passing the arguments 2 and 7. 00:35.230 --> 00:46.160 And we would expect the two to the power of seven and it's 128 and before we move on I want to make 00:46.160 --> 00:49.310 clear the difference between perimeter and argument. 00:49.310 --> 00:54.000 So many people mix those two up and also I do this sometimes. 00:54.110 --> 00:57.620 So here in this function x and y are paramount. 00:57.640 --> 01:06.420 So these are the names that appear in the function definition so X and Y are our parameters and year 01:06.430 --> 01:13.350 2 and 7 arguments all values that are passed to the functions when the function is called. 01:13.360 --> 01:19.420 So this is a slight difference and I just want to to make it clear and if you mix it up it's actually 01:19.420 --> 01:20.310 not so serious. 01:20.320 --> 01:25.320 So everybody understands what you mean by saying argument or parameter. 01:25.780 --> 01:27.080 And in this example here. 01:27.090 --> 01:37.190 So 2 and 7 are two positional arguments because Python automatically assumes that two stands for X and 01:37.230 --> 01:45.570 seven for Y because exists the first parameter and y is the second parameter and consequently two is 01:45.770 --> 01:53.970 the argument for the first parameter and 7 the argument for the second parameter and you can also make 01:53.970 --> 01:55.380 this more explicit. 01:55.410 --> 01:59.950 And by saying okay exist too and Y is seven. 02:00.720 --> 02:08.060 And in this case 2 1 7 are so-called keyword arguments because you explicitly say okay. 02:08.080 --> 02:11.270 And my part of me to exist 2 and my parameter y is 7 02:14.450 --> 02:20.560 so in this case of course the same side and what you can do you can change the position of the keyword 02:20.600 --> 02:21.170 arguments. 02:21.170 --> 02:27.830 So instead of saying X is true into y 7 you can also say y 7 and X is 2 that's the problem. 02:27.830 --> 02:34.860 So there's no danger that the Python could mix it up. 02:34.890 --> 02:42.150 Now what if we use a keyword argument for the parameter X and a persistent argument for parameter y. 02:43.110 --> 02:44.810 So let's look what we get here. 02:45.990 --> 02:54.520 And here we get the error message position argument follows keyword argument so whenever you use a mix 02:54.520 --> 02:59.970 of a keyword and positional arguments the positional arguments have to come first. 02:59.980 --> 03:05.090 So you must not start with the keyboard arguments otherwise to get an error message. 03:07.950 --> 03:15.250 But what you can do you can pass them the positional argument to for the parameter X and then apply 03:15.250 --> 03:19.440 the keyword argument 7 to about parameter y. 03:19.470 --> 03:28.330 So this works and what we can also do we can define default values for all parameters so we can define 03:28.360 --> 03:36.010 the function power to with the default values to for our paramedics and seven for our parameter y 03:40.620 --> 03:45.480 and then we can call our function without any arguments over so with the default values 03:49.450 --> 03:55.730 and of course we can also call our function with the new values and to positional arguments. 03:55.810 --> 04:00.410 So three for our perimeter except to follow our perimeter by 04:05.850 --> 04:12.100 and instead of using two positional arguments 3 and 2 we can also use to keyword arguments. 04:12.730 --> 04:15.490 X equals three and Y equals two. 04:16.450 --> 04:20.760 So this is more explicit and they are actually better to read for everyone 04:26.390 --> 04:34.040 now what they fear only wanted change parameter X so we have by default x equals two and Y equals seven. 04:34.040 --> 04:43.200 And if we say that okay except B three then Python automatically assumes the default value for y. 04:43.420 --> 04:52.350 So this works in three to the power of seven and if you only want to change X you can also take a new 04:52.350 --> 05:01.360 position the argument for our parameter X so if you only pass here the argument three paces automatically 05:01.600 --> 05:11.830 assumes that three it stands for X and we have the default value 7 for y and this gives them the same 05:11.830 --> 05:12.330 result. 05:15.320 --> 05:18.230 Now what if we only want to change our parameter y. 05:19.100 --> 05:26.720 So if we use a positional argument for why and place it here at the beginning and Python has a problem 05:26.750 --> 05:29.660 the cost Python thinks okay. 05:30.090 --> 05:37.340 3 stands for X and then if you define x equals 2 then our function got multiple values for the argument 05:37.400 --> 05:37.820 X 05:40.980 --> 05:42.120 and same as before. 05:42.120 --> 05:48.780 So if we start with them the keyword argument for x x equals 2 and then assume that Y is 3. 05:48.780 --> 05:50.330 This also does not work. 05:52.840 --> 05:54.630 Because position arguments. 05:54.650 --> 05:55.380 Uh here. 05:55.410 --> 05:55.670 Um. 05:55.690 --> 05:59.470 3 for y follows and the keyboard argument and this does not work. 06:01.330 --> 06:09.180 But what we can do we can just say okay our Y is 3 and 4 x we want to have our default value networks 06:12.220 --> 06:19.270 and we can make it more explicit by passing the 2 keyboard arguments or saying Okay X is 2 It's the 06:19.270 --> 06:27.240 same s and the default value and why should be 3 and in my opinion this is definitely best practice 06:27.480 --> 06:31.020 because everybody sees and knows at a first glance. 06:31.190 --> 06:31.410 Yeah. 06:31.410 --> 06:35.150 The arguments for for the parameters exist to win. 06:35.150 --> 06:35.960 Y is 3 06:39.870 --> 06:40.460 all right. 06:40.470 --> 06:47.790 So now coming to a completely different topic we can also assign a variety to our return value. 06:47.900 --> 06:56.030 So yeah our function power to returns um the value 8 in this case and we can directly assign the arrival 06:56.120 --> 07:01.690 set so set should be 8 and this correct. 07:01.700 --> 07:02.050 All right. 07:02.060 --> 07:08.150 So this last part 2 of user defined functions and in the next session we will learn that a function 07:08.150 --> 07:14.600 can also return multiple values and we will also have a look at uh yeah two case studies so hope to 07:14.600 --> 07:15.530 see you there by.