1 00:00:00,390 --> 00:00:04,980 All right. So we're now onto our final list comprehension exercise of the day. 2 00:00:05,580 --> 00:00:10,260 And just a word of warning, this exercise is quite hard. 3 00:00:10,710 --> 00:00:15,710 I decided that the previous two were a little bit easier and you've now kind of 4 00:00:15,900 --> 00:00:20,430 warmed up and you've gotten going, it's time to test your knowledge on a number 5 00:00:20,430 --> 00:00:21,330 of things that you've learned. 6 00:00:22,200 --> 00:00:26,970 The first thing I want you to do is take a look at these two files and look at 7 00:00:26,970 --> 00:00:29,340 the structure of the data in there, 8 00:00:29,970 --> 00:00:34,650 and then have a read through the instruction and see if you can complete this 9 00:00:34,680 --> 00:00:35,513 challenge. 10 00:00:35,700 --> 00:00:40,700 This is the output that you are expecting when your new list called result is 11 00:00:40,830 --> 00:00:44,100 printed. Pause the video and give this a go. 12 00:00:47,670 --> 00:00:48,030 All right. 13 00:00:48,030 --> 00:00:53,030 So we know that we've got two text files with a new piece of data on each line. 14 00:00:54,900 --> 00:00:55,440 Essentially, 15 00:00:55,440 --> 00:01:00,390 what we're trying to do here is we're trying to take the data in file1. 16 00:01:00,390 --> 00:01:04,890 txt and compare it against the data in file2.txt, 17 00:01:05,310 --> 00:01:09,750 and then we're trying to get a hold of the data which exists in both of these 18 00:01:09,750 --> 00:01:14,670 files. So if file1 contained one, two, three, file2 contained two, 19 00:01:14,670 --> 00:01:15,503 three, four, 20 00:01:15,690 --> 00:01:20,250 then the result should be a list that contains the overlapping numbers. 21 00:01:20,550 --> 00:01:24,750 Two and three exists in both files. Now, 22 00:01:24,750 --> 00:01:29,370 in order to pass the test, the result must be a list that contains integers, 23 00:01:29,430 --> 00:01:33,180 so whole numbers, not strings. So when you print it out, 24 00:01:33,300 --> 00:01:37,470 if you see the numbers as they are, then that means they are integers. 25 00:01:37,800 --> 00:01:40,560 But if you see quotation marks around each of the numbers, 26 00:01:40,800 --> 00:01:42,450 then they are strings instead. 27 00:01:42,900 --> 00:01:45,990 And our code checking is not going to allow that to pass. 28 00:01:47,190 --> 00:01:52,190 The first thing we need to do is to use our read lines method that we've used 29 00:01:52,320 --> 00:01:57,320 several times before to read the data from each of these files and create a list 30 00:01:57,780 --> 00:02:00,780 from each line. Let's go ahead and do that. 31 00:02:00,990 --> 00:02:05,430 So I'm going to use my with open and I'm going to tap into my file1. 32 00:02:05,430 --> 00:02:09,000 txt, and I'm going to save this as file1. 33 00:02:09,900 --> 00:02:13,710 And then this file is going to be read, 34 00:02:13,950 --> 00:02:16,800 and I'm going to call file1.readlines, 35 00:02:17,220 --> 00:02:22,220 and then I'm going to save this list to a new variable called file_1_data. And 36 00:02:25,260 --> 00:02:27,510 notice how I've actually made a typo here 37 00:02:27,510 --> 00:02:31,680 cause I want file1.txt instead of just file.text. 38 00:02:32,010 --> 00:02:33,120 It's good that I spotted it. 39 00:02:34,320 --> 00:02:39,320 And then we're going to do the same with file2 and change all of the places 40 00:02:39,960 --> 00:02:40,890 where we have one. 41 00:02:41,520 --> 00:02:45,180 So copying and pasting is always a little bit prone to error, 42 00:02:45,360 --> 00:02:47,490 but hopefully we'll manage this time. 43 00:02:48,270 --> 00:02:53,130 Now that I've got file_1_data and file_2_data which are both lists, 44 00:02:53,490 --> 00:02:58,490 I can now think about how I can compare those two and create my new list 45 00:02:59,440 --> 00:03:01,300 which is going to be called result. 46 00:03:02,410 --> 00:03:07,410 Now result is a new list and I'm going to use my full list of keywords 47 00:03:09,010 --> 00:03:12,670 inside this new list to create the list comprehension. 48 00:03:13,000 --> 00:03:17,500 So new item for item in lists if test, 49 00:03:18,340 --> 00:03:23,020 the list that I'm going to test is actually the first list. 50 00:03:23,590 --> 00:03:27,460 I'm going to take the file_1_data which is a list of numbers, 51 00:03:28,090 --> 00:03:33,090 and then I'm going to go through each of the numbers inside this list, 52 00:03:35,350 --> 00:03:37,300 and then I'm going to do a check. 53 00:03:37,900 --> 00:03:42,070 And the check is where this file2 is going to come into play. 54 00:03:42,640 --> 00:03:44,200 So I'm going to check to see, well, 55 00:03:44,290 --> 00:03:48,850 if this number that I'm looping through exists in, 56 00:03:48,880 --> 00:03:50,350 remember the in keyword, 57 00:03:50,620 --> 00:03:54,010 this file_2_data, this other list, 58 00:03:54,340 --> 00:03:58,870 well then I'm going to include this number inside my new list. 59 00:03:59,860 --> 00:04:04,360 So this number is going to go into the new list. At the moment when I hit run, 60 00:04:04,420 --> 00:04:08,170 you can see them getting a whole bunch of strings. So in addition, 61 00:04:08,200 --> 00:04:13,030 I have to modify this number so that I convert it into an integer. 62 00:04:13,510 --> 00:04:17,650 So I end up with the same output as is expected here. 63 00:04:19,390 --> 00:04:21,940 Did you remember all of the things that we've learned before 64 00:04:21,940 --> 00:04:26,940 like the in and the with open and also the converting to int? 65 00:04:27,790 --> 00:04:31,810 Did you manage to complete this challenge? If you had any trouble at all, 66 00:04:31,960 --> 00:04:34,840 be sure to review the relevant parts, for example, 67 00:04:35,080 --> 00:04:40,060 opening files or reading lines from the files which we covered in previous days. 68 00:04:40,690 --> 00:04:43,540 Alternatively, if it's the list comprehension that's hard, 69 00:04:43,930 --> 00:04:45,400 then be sure to review the list 70 00:04:45,400 --> 00:04:50,020 comprehension lesson in today's course and make sure that you really understand 71 00:04:50,020 --> 00:04:52,600 what's going on in the code before you continue.