WEBVTT 00:00.740 --> 00:06.710 Often you will want to start with an existing list and make an entirely new list based on the first 00:06.710 --> 00:06.980 one. 00:06.980 --> 00:14.370 So let's explore how copying a list works and examine one situation in which copying a list is useful. 00:14.390 --> 00:21.080 So to copy a list, you can make a slice that includes the entire original list by omitting the first 00:21.080 --> 00:24.290 index and the second index like this. 00:25.410 --> 00:25.930 Right. 00:26.170 --> 00:33.340 So this tells Python to make a slice that starts at the first item and ends with the last item producing 00:33.340 --> 00:35.110 a copy of the entire list. 00:35.230 --> 00:42.550 For example, imagine we have a list of four list of our favorite car makers and want to make a separate 00:42.550 --> 00:47.470 list of car makers that our friend drives. 00:47.470 --> 00:53.710 So this friend likes everything in our list and drives everything on our list so far so we can create 00:53.740 --> 00:56.660 their list by copying ours. 00:56.690 --> 01:03.160 So in order to do that, you will write friend's friend that. 01:05.610 --> 01:07.140 Friend that. 01:08.150 --> 01:10.310 Likes cars. 01:10.310 --> 01:14.030 And here we will use this and let's actually my. 01:15.280 --> 01:17.140 My favorite. 01:19.710 --> 01:21.150 Custom cars. 01:21.150 --> 01:22.380 And here. 01:23.280 --> 01:24.060 Friends. 01:29.940 --> 01:31.200 And here. 01:31.890 --> 01:33.480 Now we will use this. 01:33.510 --> 01:35.310 My favorite cars. 01:35.580 --> 01:36.570 And this. 01:37.760 --> 01:39.050 And after that we will. 01:39.050 --> 01:39.890 Uh, firstly. 01:40.860 --> 01:45.090 Prentiss Brown's favorite cars and after that. 01:45.090 --> 01:50.790 So firstly, of course, this is the friend favorite cars and this is my favorite cars. 01:50.790 --> 01:55.380 And after that we first we will first print the my favorite cars. 01:55.380 --> 01:56.790 So print. 01:58.000 --> 01:59.920 My favorite. 02:02.030 --> 02:04.580 Cars are like this. 02:04.580 --> 02:07.670 And after that we will print our my favourite cars. 02:07.760 --> 02:09.740 And after that we will print. 02:09.770 --> 02:12.140 Of course we need to add new line before it. 02:12.200 --> 02:14.750 So my friends. 02:17.650 --> 02:21.220 Favorite cars are here. 02:21.340 --> 02:22.960 And after that we will print. 02:23.450 --> 02:24.430 Friends. 02:25.000 --> 02:25.900 Friends. 02:25.900 --> 02:26.950 Favorite cars. 02:27.870 --> 02:30.480 And here we will run this now. 02:30.480 --> 02:32.480 And as you can see, this is our output. 02:32.490 --> 02:35.760 So I added this new line here. 02:35.790 --> 02:37.440 Oops, sorry again. 02:41.290 --> 02:42.700 It's not working or. 02:42.700 --> 02:44.320 Yes, it's working now. 02:44.350 --> 02:44.830 Okay. 02:45.930 --> 02:52.140 So here I added this new line character to this to show our output. 02:52.170 --> 02:53.040 New line here. 02:53.040 --> 02:56.010 So I could we added this new line after the. 02:58.400 --> 03:01.310 My favorite cars here, but it's more easy to add here. 03:01.310 --> 03:07.430 Instead of writing some formatting and things in last my favorite cars print function. 03:07.760 --> 03:18.950 So first we make a list of car makers we we like called or favorite car makers called my favorite cars. 03:18.950 --> 03:24.470 Then we make a new list called Friends, Friends, Favorite Cars. 03:24.830 --> 03:34.880 And we make a copy of my favorite cars by asking for a slice of my favorite cars without specifying 03:34.880 --> 03:36.950 an indicator like this here. 03:37.840 --> 03:43.060 And assign the copy of my favorite cars to. 03:43.890 --> 03:45.000 Friend's favorite cars. 03:45.000 --> 03:52.800 So when and when we print each list, we see that they both contain the same cars. 03:52.800 --> 03:57.090 So to prove that we actually have two separate lists, we will add a new. 03:57.830 --> 03:59.380 Uh, we will add a new. 04:02.200 --> 04:09.640 Favor of a new car to each list and show that we that each list keeps track of the appropriate person's 04:09.640 --> 04:10.710 favorite car. 04:10.720 --> 04:15.880 So in order to do that, we will do after my favorite cars here we will do. 04:18.700 --> 04:19.540 My. 04:21.120 --> 04:24.510 My favorite cars that append here. 04:24.540 --> 04:29.550 Let's add new car maker name in this case, Toyota. 04:29.550 --> 04:30.010 Right. 04:30.030 --> 04:31.920 So Toyota. 04:33.500 --> 04:33.620 Of. 04:35.100 --> 04:35.970 Toyota here. 04:35.970 --> 04:42.690 And after that, we will also add friends favorite cars and we will append the. 04:44.230 --> 04:44.990 No, that's sad. 04:49.500 --> 04:50.430 Fiat, right? 04:51.500 --> 04:52.700 And here. 04:53.630 --> 04:59.690 We will not change this print functions and now we will run our code and see what will change here. 04:59.690 --> 05:07.640 And as you can see here, so we copy the original items in my favorite cars to the new list called Friends 05:07.640 --> 05:10.460 Favorite Cars, as we did in the previous example. 05:10.460 --> 05:19.550 And next we add a new favorite new car maker to each list and we add Toyota to my favorite cars and 05:19.550 --> 05:22.940 we add fiat to friends, favorite cars. 05:22.940 --> 05:31.210 And when and we then print the to list to see whether their whether each of these favorite cars in the 05:31.250 --> 05:32.660 is in the appropriate list. 05:32.660 --> 05:36.020 So here the output shows that our. 05:37.140 --> 05:40.710 Toyota is appears in our list of favorite cars. 05:40.710 --> 05:43.320 But Fiat here. 05:43.350 --> 05:45.450 Fiat does not. 05:45.450 --> 05:51.390 So we can see that Fiat now appears in our friends list. 05:51.780 --> 05:53.780 But Toyota doesn't write. 05:53.790 --> 06:01.980 If you had a simple set friend, favorite friends, favorite cars equal to my favorite cars, we will 06:01.980 --> 06:03.330 not produce two separate lists. 06:03.330 --> 06:11.490 For example, here's what happens when you try to copy a list without using a slice. 06:17.560 --> 06:18.940 Without using a slice. 06:19.180 --> 06:22.000 And as you can see here, we both have. 06:22.570 --> 06:30.940 So instead of assigning a copy of my foods to my my favorite cars, to my friend's favorite cars, we 06:30.940 --> 06:34.690 set a friend's favorite cars equal to my favorite cars. 06:34.690 --> 06:41.380 So this syntax actually tells Python to associate the new variable to my favorite cars with a list that 06:41.380 --> 06:45.400 is already associated with my favorite cars. 06:45.400 --> 06:47.830 So now my favorite cars. 06:47.830 --> 06:52.150 It will also appear in friends, favorite cars and so on. 06:52.150 --> 06:59.770 So likewise, the Toyota will appear in both lists, even though or Fiat will appear in both lists, 06:59.770 --> 07:03.280 even though it appears to be added only to my favorite cars. 07:03.280 --> 07:08.110 And as you can see here, Toyota and Fiat appears in the same list. 07:08.110 --> 07:16.270 So the output shows that both lists are the same now, which is not we wanted here and don't worry about 07:16.270 --> 07:17.600 the details in this example. 07:17.600 --> 07:23.360 For now, if you are trying to work with the with a copy of list and you see an expected behavior, 07:23.360 --> 07:30.080 make sure you are copying the list using a slice as we did in this in the first example here.