WEBVTT 00:00.500 --> 00:05.330 In previous section, you learned how to make a simple list and you learned how to work with individual 00:05.330 --> 00:06.170 elements in list. 00:06.800 --> 00:12.730 In this section, you will learn how to loop through an entire list using just a few lines of code, 00:12.740 --> 00:15.270 regardless of how long the list is. 00:15.290 --> 00:21.350 So looping allows you to make the same action or set of actions with every item in a list. 00:21.380 --> 00:27.590 As a result, you will be able to work efficiently with a list of any length, including those with 00:27.680 --> 00:29.630 thousands or even millions of items. 00:30.620 --> 00:37.340 And you will often want to run through all entries in the list. 00:38.740 --> 00:42.220 So performing the same task with each item. 00:42.220 --> 00:46.720 For example, in a game you might want to move every element. 00:47.560 --> 00:53.350 But on the screen to the same account practice. 00:55.800 --> 01:02.460 Um, or in a list of numbers you might want to perform the same statistical operation on every element. 01:02.460 --> 01:08.700 Or perhaps you will want to display each headline from a list of articles on a website. 01:08.700 --> 01:15.330 So when you want to do the same action with every item in a list, you can use The python's for loop, 01:15.780 --> 01:17.250 Python's for loop. 01:17.640 --> 01:24.210 So say we have a list of magician's names and we want to print out each name in the list. 01:25.190 --> 01:29.720 We could do this by retrieving each name from the list individually, but this approach could cause 01:29.720 --> 01:30.950 several problems here. 01:30.980 --> 01:35.810 For one, it would be repetitive to do this with a long list of names. 01:35.840 --> 01:42.470 Also, we'd have to change our code each time the list length created and using the for loop avoids 01:42.470 --> 01:48.530 both of these uses by letting Python manage these uses internally. 01:48.530 --> 01:52.640 So let's use a for loop to print out each name in a list of magicians. 01:52.640 --> 01:57.740 So here actually mutations. 02:01.930 --> 02:02.650 So just like that. 02:02.650 --> 02:03.160 Yes. 02:03.340 --> 02:04.860 So, magicians. 02:04.900 --> 02:07.330 And let's actually make it Alice. 02:10.010 --> 02:10.760 Alice. 02:10.940 --> 02:11.990 David. 02:13.650 --> 02:15.690 David and Carolina. 02:17.880 --> 02:20.010 And here we will create a for loop here. 02:20.010 --> 02:22.350 So for magician. 02:24.030 --> 02:25.860 In magicians. 02:26.570 --> 02:31.430 And after that we will print the magician every time. 02:32.300 --> 02:39.890 And here we begin by defining a list, just as we did in previous lectures. 02:39.920 --> 02:40.280 Oops. 02:40.280 --> 02:42.690 Here, let me fix my mouse right now. 02:42.710 --> 02:43.430 Yes. 02:43.550 --> 02:44.690 So here we go. 02:44.780 --> 02:50.630 We begin by defining a list, just as we did in previous lectures here. 02:52.280 --> 02:53.120 So. 02:54.580 --> 02:56.320 Then we define a for loop. 02:56.320 --> 02:57.910 This is new to us, right? 02:58.060 --> 03:02.050 So then we define the for loop. 03:03.210 --> 03:05.310 So this line. 03:06.070 --> 03:10.690 Tells Python to pull a name from the list. 03:10.720 --> 03:12.370 Magicians. 03:13.600 --> 03:14.350 And. 03:15.170 --> 03:18.950 Associated with the variable name magician. 03:20.180 --> 03:29.810 Next we tell Python to print the name that just been assigned to this magician here. 03:32.370 --> 03:37.380 Biden then repeats these last two lines, one for each name in the list. 03:37.410 --> 03:41.320 It might help to read this code as like this. 03:41.340 --> 03:46.170 So here we for this code, we have this explanation. 03:51.450 --> 03:57.210 Every magician in the list of magicians. 03:59.570 --> 04:00.650 Magicians. 04:03.450 --> 04:06.120 Print the magician's. 04:09.070 --> 04:09.520 Nay. 04:12.080 --> 04:16.520 So the output is simple printout of each name in the list. 04:16.550 --> 04:17.780 Let's try this out. 04:21.360 --> 04:30.450 As you can see here, we printed every user in the in the our magicians list without a problem. 04:32.470 --> 04:37.840 Now looping is important because it's one of the most common ways of computer automates repetitive tasks. 04:37.870 --> 04:44.860 For example, in a simple loop like we used in this file, in this lecture. 04:45.810 --> 04:46.560 Here. 04:47.880 --> 04:52.270 Python initially reads the first line of the loop. 04:52.290 --> 04:53.400 This line here. 04:53.550 --> 05:01.950 So this line tells Python to retrieve the first value from the list magicians and associated with the 05:01.950 --> 05:05.450 variable magician and the first value here. 05:05.460 --> 05:09.240 So here, actually, let me write that down here. 05:10.210 --> 05:10.810 Okay. 05:10.810 --> 05:14.500 So the first value here, The first. 05:14.530 --> 05:15.400 Oh, sorry. 05:16.000 --> 05:16.480 Here. 05:16.480 --> 05:18.640 The first value here. 05:19.420 --> 05:21.490 Is Alice, right? 05:21.640 --> 05:22.400 Yes. 05:22.420 --> 05:25.090 The first value here is. 05:29.420 --> 05:30.980 And the second value. 05:32.270 --> 05:38.390 And I'll also python prints the first value as Alice and the current. 05:38.510 --> 05:43.730 This is the current value of magician right now which is still Alice because the list contains more 05:43.730 --> 05:49.850 values and Python returns to the first line of the loop. 05:50.090 --> 05:50.960 Right. 05:51.320 --> 05:56.630 So Python retrieves the next name in the list, which is. 05:58.280 --> 05:59.120 In this case. 05:59.120 --> 06:00.110 David Right. 06:00.110 --> 06:02.420 So Python also retrieves the. 06:02.420 --> 06:03.050 David. 06:06.980 --> 06:12.950 And associates that value within the variable magician here. 06:13.250 --> 06:20.720 And Python then executes the line which is print the magician and Python prints the current value of 06:20.720 --> 06:28.760 magician again which is now is David and Python repeats the entire loop once more with the last value 06:28.760 --> 06:31.700 in the list, which is Caroline. 06:32.000 --> 06:33.470 This here. 06:34.080 --> 06:36.330 So because no more values are in the list. 06:36.330 --> 06:39.900 Python moves on to the next line of the program. 06:39.900 --> 06:41.970 In this case, nothing. 06:42.000 --> 06:45.750 Nothing comes after this line here. 06:46.590 --> 06:48.900 So this is empty here for now. 06:50.450 --> 06:51.020 And. 06:53.490 --> 06:55.980 And nothing comes after the for loop. 06:55.980 --> 06:59.160 And so for loop will end here. 06:59.160 --> 07:05.610 So when you are using the loops for the first time, keep in mind that the set of steps is repeated 07:05.610 --> 07:07.980 once for each item in the list. 07:07.980 --> 07:12.630 So no matter how many items are in the list and how much. 07:12.630 --> 07:19.050 So if you have a million items in your list, the python repeats these steps a million times and usually 07:19.050 --> 07:19.950 very quickly. 07:20.320 --> 07:26.820 Also, keep in mind when writing your own for loops that you can choose any name you want for the temporary 07:26.820 --> 07:27.600 variable. 07:28.660 --> 07:30.850 That will be associated with each value in the list. 07:30.850 --> 07:35.710 So however itself will do, choose a meaningful name that represents a single item for the list. 07:35.920 --> 07:38.920 So for example, you can. 07:39.310 --> 07:45.040 Let's actually create a good way to for naming these loops here. 07:45.760 --> 07:56.200 So another good way for naming this loop is, for example, look for Cat in cats or for dog in dogs 07:56.230 --> 08:02.710 or for item in list of items. 08:02.740 --> 08:07.120 Okay, so these are the just examples that you can name your loops. 08:07.120 --> 08:10.430 So to make it more meaningful and readable. 08:10.450 --> 08:10.990 Right. 08:10.990 --> 08:17.710 So these naming conventions can help you to follow the action behind being done on each item within 08:17.710 --> 08:18.610 a for loop. 08:19.120 --> 08:24.190 And using singular and plural names can help you identify whether a section of code is working with 08:24.190 --> 08:28.820 a single element from the list or the entire list at.