1 00:00:04,560 --> 00:00:09,840 Strings have a join method that's very useful for producing output from a list, 2 00:00:09,840 --> 00:00:13,280 and in fact, it can be used with any iterable. What I'm going to do is use the 3 00:00:13,280 --> 00:00:19,550 first for loop in our nospam program, for this example. What I'm going to do is 4 00:00:19,550 --> 00:00:28,640 uncomment the first loop, then I'm going to delete the rest of the code below that. 5 00:00:28,640 --> 00:00:31,300 Alright, now I've done that, I'm going to run the program to remind 6 00:00:31,300 --> 00:00:35,560 ourselves of the output, and you can see that we've got the eight meals printed out, 7 00:00:35,560 --> 00:00:39,880 with the spam removed. Each line of the output is enclosed in square 8 00:00:39,880 --> 00:00:44,059 brackets, and each string in the list is enclosed in a single quote - that's how 9 00:00:44,059 --> 00:00:50,210 Python prints lists by default. Now we can use join to tidy this up, so let's have 10 00:00:50,210 --> 00:00:56,180 a go of doing that. I'm going to change line 17 to type, in those parentheses, 11 00:00:56,180 --> 00:01:01,309 double quotes comma and a space and double quotes. Then I'm going to type dot 12 00:01:01,309 --> 00:01:10,280 join, and then meal in parentheses. So let's run that and then I'll explain 13 00:01:10,280 --> 00:01:16,159 what it's doing. So you can see that, now that we've run that, the output was what 14 00:01:16,159 --> 00:01:20,299 we wanted at the end of the previous video. The items in each meal are printed 15 00:01:20,299 --> 00:01:25,520 on the same line, separated by a comma and a space. Now the comma and space 16 00:01:25,520 --> 00:01:30,890 come from the string that we called join on, on line 17. This example might be a 17 00:01:30,890 --> 00:01:35,149 bit confusing. We can see that join is useful, but you may find it hard to 18 00:01:35,149 --> 00:01:40,039 understand what it's doing, because we're using it inside a loop. Let's see some 19 00:01:40,039 --> 00:01:44,299 simpler examples. I'm going to create a new Python file. I don't want to call 20 00:01:44,300 --> 00:01:47,780 the file join, because that's the name of the method we're using. 21 00:01:47,780 --> 00:01:52,300 Avoid using Python names for your files because it can cause problems. Right, so 22 00:01:52,310 --> 00:01:56,859 I'm gonna call this one joining_things.py. 23 00:02:04,460 --> 00:02:08,580 We're gonna start by creating a list and then printing out its items. So I'm going 24 00:02:08,580 --> 00:02:13,820 to type flowers is equal to, left square bracket, and on the next line I'm going 25 00:02:13,830 --> 00:02:21,120 to start typing , I'll start with Daffodil comma, next line Evening 26 00:02:21,120 --> 00:02:32,140 Primrose comma - obviously, these are in double quotes, next line Hydrangea, 27 00:02:32,140 --> 00:02:37,140 comma to go to the next line, Iris on the next line comma. Next line, 28 00:02:37,140 --> 00:02:52,120 Lavender, next line, Sunflower, next line, one last one, Tiger Lily. 29 00:02:52,120 --> 00:02:58,040 Then we'll print them out by typing for flower in flowers: 30 00:02:58,040 --> 00:03:06,740 print flower, and there's no surprises when I run that. We get each of the 31 00:03:06,750 --> 00:03:11,430 flowers printed out. What we've done there is, iterated over the list and 32 00:03:11,430 --> 00:03:17,160 printed each item. The join method actually takes care of iterating for us. 33 00:03:17,160 --> 00:03:22,500 We give it an iterable and it joins all the items in the iterable. It uses the 34 00:03:22,500 --> 00:03:28,169 string we call it on as the separator. Now a list is an iterable, so we can pass 35 00:03:28,169 --> 00:03:32,370 our flowers list to the join method. So what I'm going to do is comment out this 36 00:03:32,370 --> 00:03:42,510 for loop. Alright, so I'm going to type separator is equal to double quotes - I'm 37 00:03:42,510 --> 00:03:48,720 going to use a pipe character, with a space to the left and right of it. 38 00:03:48,720 --> 00:03:52,200 Then I'm going to type, on the next line, output is equal to separator 39 00:03:52,200 --> 00:04:01,310 dot join, then in parentheses, flowers. Then I'm going to print output. 40 00:04:02,140 --> 00:04:05,890 Now we could write all that on one line, but I've split each part up to make it 41 00:04:05,890 --> 00:04:10,780 easier to understand. Join is a string method, and we start with a string 42 00:04:10,780 --> 00:04:16,640 on line 14. I called a string separator, so it's clear how the string is used. 43 00:04:16,640 --> 00:04:21,940 On line 15, we call the join method. That will iterate over the flowers list and 44 00:04:21,940 --> 00:04:29,080 create a string containing each flower, separated by space bar space. The bar is 45 00:04:29,080 --> 00:04:32,140 also known as pipe - I refer to that as the pipe character bur bar is 46 00:04:32,140 --> 00:04:36,610 another word for it. Now I'm using dot notation there. Join is a method of the 47 00:04:36,610 --> 00:04:44,860 str class, and separator is a string. So if I run the program now, and that's the 48 00:04:44,860 --> 00:04:49,620 output we get. Each of the flowers has been joined into a single string, 49 00:04:49,620 --> 00:04:55,140 with space bar space between each one. Now we could use a comma and a space instead, 50 00:04:55,140 --> 00:05:00,940 so let's change that. Remove one of the spaces, then just change that to a comma 51 00:05:00,940 --> 00:05:07,960 space. Run that. This time, as you can see, there's a comma and a space between 52 00:05:07,960 --> 00:05:13,479 each flower. Now note that we haven't had to use a for loop here. Join iterates 53 00:05:13,479 --> 00:05:18,400 over the list for us. Alright, so that's the join method. It creates a string from 54 00:05:18,400 --> 00:05:23,320 a list, and separates each item with the string that it's called on. So experiment 55 00:05:23,320 --> 00:05:27,720 with different lists and strings. Remember you can also use string literals, 56 00:05:27,720 --> 00:05:35,520 so you could type, line 18, print parentheses, comma in double 57 00:05:35,520 --> 00:05:47,300 quotes, then dot join, and in parentheses, flowers. If you run that, 58 00:05:47,300 --> 00:05:52,160 and you can see that's separated each flower with just a comma. Now before I 59 00:05:52,160 --> 00:05:55,820 finish the video, there is one thing to be aware of - all the items in the 60 00:05:55,820 --> 00:06:01,010 iterable must be strings, if you want to join the items. For example, if I go back 61 00:06:01,010 --> 00:06:09,220 up to our list, and I add a number - an int - to our list down here, 62 00:06:09,220 --> 00:06:15,680 the code will actually crash. So if we run that, you can see we've got an error. Join can't join 63 00:06:15,680 --> 00:06:20,270 ints to the string that it produces. Alright, so let's finish the video now, with 64 00:06:20,270 --> 00:06:24,110 a quick look at what the documentation says about lists. I'm going to paste the 65 00:06:24,110 --> 00:06:27,340 link into a into the browser. 66 00:06:33,590 --> 00:06:38,310 Right, so the first paragraph says that lists are typically used to store 67 00:06:38,310 --> 00:06:44,380 collections of homogeneous items. Homogeneous, here, means items of the same type. 68 00:06:44,380 --> 00:06:48,800 Our original list was homogeneous because all the items were strings. 69 00:06:48,800 --> 00:06:55,420 So I'll switch back to our code, so we can see our list again. 70 00:06:55,420 --> 00:06:59,660 So lists are typically used to store homogeneous items, but you are free to store just 71 00:06:59,670 --> 00:07:03,210 about anything you want in them. Just be aware of the problems that can cause, 72 00:07:03,210 --> 00:07:07,530 when you come to process the list. Our code worked fine when all the items were 73 00:07:07,530 --> 00:07:11,550 strings, but you saw it crash when we added in integer value. Now this is 74 00:07:11,550 --> 00:07:16,280 something we often get asked about, so I'm taking the opportunity to clarify it here. 75 00:07:16,280 --> 00:07:19,800 Python will let you store different types in a list. What the documentation 76 00:07:19,800 --> 00:07:25,170 is saying, is that lists are intended to be homogeneous, but that's not enforced 77 00:07:25,170 --> 00:07:27,870 by the compiler. Sometimes there's a good case for 78 00:07:27,870 --> 00:07:32,190 storing different types in a list - just be aware that you may run into problems 79 00:07:32,190 --> 00:07:36,060 processing the items in a list, if they're not all of a similar type. 80 00:07:36,060 --> 00:07:40,520 Alright, so let's end the video here. In the next one, we'll look at the opposite of join 81 00:07:40,520 --> 00:07:45,080 - the split method. See you in the next video.