1 1 00:00:01,180 --> 00:00:02,680 Hi guys and welcome back. 2 2 00:00:02,680 --> 00:00:04,220 In this video, we're going to talk about 3 3 00:00:04,220 --> 00:00:06,623 string formatting in Python. 4 4 00:00:07,480 --> 00:00:08,940 Specifically, we're going to be using 5 5 00:00:08,940 --> 00:00:13,340 a newer Python feature from Python 3.6 onwards. 6 6 00:00:13,340 --> 00:00:14,410 So for this video, 7 7 00:00:14,410 --> 00:00:18,590 make sure that you're using Python 3.6 or later. 8 8 00:00:18,590 --> 00:00:20,427 Let's say that you've got two strings, 9 9 00:00:20,427 --> 00:00:24,269 one, which is Bob, and has the name of 'name,' 10 10 00:00:24,269 --> 00:00:26,010 and one which is Hello, Bob and has the name of 'greeting.' 11 11 00:00:28,610 --> 00:00:30,964 If you print greeting out, of course 12 12 00:00:30,964 --> 00:00:32,796 line:15% you're going to get, 13 13 00:00:32,796 --> 00:00:37,420 line:15% Hello Bob, since that are the contents of the string. 14 14 00:00:37,420 --> 00:00:40,528 But if you set 'name' to Rolf 15 15 00:00:40,528 --> 00:00:43,380 and then you print greeting again, 16 16 00:00:43,380 --> 00:00:45,500 then naturally as you run that, 17 17 00:00:45,500 --> 00:00:49,420 line:15% you're gonna get Hello, Bob and then Hello, Bob again. 18 18 00:00:49,420 --> 00:00:53,950 Greeting contains the string name, which is Bob, 19 19 00:00:53,950 --> 00:00:57,320 but it doesn't calculate it dynamically, 20 20 00:00:57,320 --> 00:00:59,900 which means that when greeting is defined, 21 21 00:00:59,900 --> 00:01:04,900 it contains the characters Hello comma space Bob. 22 22 00:01:05,020 --> 00:01:07,970 And then changing 'name' doesn't change that greeting. 23 23 00:01:07,970 --> 00:01:10,550 So if you wanted to change the greeting, 24 24 00:01:10,550 --> 00:01:13,250 you would have to do something a little bit different. 25 25 00:01:15,160 --> 00:01:18,403 Indeed, instead of typing, Hello comma Bob, 26 26 00:01:18,403 --> 00:01:20,444 what you'd like to do is to put an 'F' 27 27 00:01:20,444 --> 00:01:22,980 in front of the quotation marks. 28 28 00:01:22,980 --> 00:01:26,610 So now we've got what's called an F string in Python. 29 29 00:01:26,610 --> 00:01:29,810 An F string allows us to embed variables 30 30 00:01:29,810 --> 00:01:31,560 inside of strings. 31 31 00:01:31,560 --> 00:01:33,700 So here instead of Hello comma Bob, 32 32 00:01:33,700 --> 00:01:38,700 we can do Hello comma 'name' inside these curly braces. 33 33 00:01:38,960 --> 00:01:42,249 Now, again, we've got F and then inside the string, 34 34 00:01:42,249 --> 00:01:46,200 we can use the curly braces and inside the curly braces, 35 35 00:01:46,200 --> 00:01:48,850 we can put a variable name. 36 36 00:01:48,850 --> 00:01:52,090 So when this is calculated, 37 37 00:01:52,090 --> 00:01:55,190 'name' will be replaced by Bob, 38 38 00:01:55,190 --> 00:01:57,830 so we will print out Hello, Bob. 39 39 00:01:57,830 --> 00:01:58,940 So if we run that, 40 40 00:01:58,940 --> 00:02:01,780 line:15% you'll see down here that we get Hello, Bob. 41 41 00:02:01,780 --> 00:02:04,640 So exactly the same thing as before. 42 42 00:02:04,640 --> 00:02:06,820 At this point, I'll say that if you do 43 43 00:02:06,820 --> 00:02:10,034 what we had earlier and set 'name' to Rolf, 44 44 00:02:10,034 --> 00:02:11,830 and then you print greeting again, 45 45 00:02:11,830 --> 00:02:14,440 you'll have the same problem as before. 46 46 00:02:14,440 --> 00:02:15,920 line:15% So if you press play again, 47 47 00:02:15,920 --> 00:02:18,100 line:15% you'll see Hello, Bob, Hello, Bob. 48 48 00:02:18,100 --> 00:02:21,250 So what we've done here is we have embedded 49 49 00:02:21,250 --> 00:02:24,160 the variable inside the string 50 50 00:02:24,160 --> 00:02:26,540 with the value that that variable had 51 51 00:02:26,540 --> 00:02:28,630 at this point in time, in line 2. 52 52 00:02:28,630 --> 00:02:31,280 So in line 2, 'name' had the value of Bob, 53 53 00:02:31,280 --> 00:02:33,343 so greeting is Hello, Bob. 54 54 00:02:34,410 --> 00:02:36,640 So what is the point of using the F string 55 55 00:02:36,640 --> 00:02:38,930 if it doesn't change dynamically? 56 56 00:02:38,930 --> 00:02:40,470 Well, the good thing about this F string 57 57 00:02:40,470 --> 00:02:42,940 is that instead of defining a variable for it, 58 58 00:02:42,940 --> 00:02:46,190 if you wanted to have a different value each time, 59 59 00:02:46,190 --> 00:02:48,713 you could just print it out, like that, 60 60 00:02:48,713 --> 00:02:51,716 and get rid of this variable definition. 61 61 00:02:51,716 --> 00:02:54,740 Now what we've got here is we are printing 62 62 00:02:54,740 --> 00:02:56,590 and inside the brackets, we've got 63 63 00:02:56,590 --> 00:02:58,060 the value that we want to print, 64 64 00:02:58,060 --> 00:02:59,485 so here we have the F string, 65 65 00:02:59,485 --> 00:03:02,300 which includes an F, then the quotation marks, 66 66 00:03:02,300 --> 00:03:04,725 and then the characters inside it, including the variable. 67 67 00:03:04,725 --> 00:03:06,512 By doing something like this, 68 68 00:03:06,512 --> 00:03:08,578 now every time you run this code, 69 69 00:03:08,578 --> 00:03:12,100 line:15% you're going to use the name at its latest point in time, 70 70 00:03:12,100 --> 00:03:15,113 line:15% so we get Hello, Bob, and Hello, Rolf. 71 71 00:03:17,060 --> 00:03:19,154 There is a way of defining a template, 72 72 00:03:19,154 --> 00:03:22,120 which instead of calculating it at 73 73 00:03:22,120 --> 00:03:23,860 the time where it is defined, 74 74 00:03:23,860 --> 00:03:25,330 you can calculate the values 75 75 00:03:25,330 --> 00:03:27,470 to be replaced inside it later on. 76 76 00:03:27,470 --> 00:03:28,950 Here's how you do that. 77 77 00:03:28,950 --> 00:03:31,738 So you can define your greeting as 'Hello,' 78 78 00:03:31,738 --> 00:03:34,620 and then open and closing curly braces. 79 79 00:03:34,620 --> 00:03:37,710 Notice that we don't have an F in front of it. 80 80 00:03:37,710 --> 00:03:39,890 Then you can say that with 'name,' 81 81 00:03:39,890 --> 00:03:41,250 which is another variable, 82 82 00:03:41,250 --> 00:03:45,728 is greeting.format and then 'name.' 83 83 00:03:45,728 --> 00:03:47,240 So what we've done here 84 84 00:03:47,240 --> 00:03:49,722 is we have created now three strings. 85 85 00:03:49,722 --> 00:03:52,560 We have the string 'name,' which has the value Bob, 86 86 00:03:52,560 --> 00:03:54,900 we have the string 'greeting,' which is our template, 87 87 00:03:54,900 --> 00:03:57,584 which says, "Hello comma curly braces 88 88 00:03:57,584 --> 00:04:01,690 and finally we say, greeting.format 89 89 00:04:01,690 --> 00:04:05,190 and then inside brackets, we put in the name. 90 90 00:04:05,190 --> 00:04:07,056 So what this is doing is essentially it's calling 91 91 00:04:07,056 --> 00:04:09,640 the format function 92 92 00:04:09,640 --> 00:04:13,320 inside of 'greeting' and what that's doing is, 93 93 00:04:13,320 --> 00:04:16,730 it is giving the name to this template, 94 94 00:04:16,730 --> 00:04:19,400 and what the template will do is it will 95 95 00:04:19,400 --> 00:04:20,810 replace the curly braces 96 96 00:04:20,810 --> 00:04:23,790 by the contents of the 'name' variable. 97 97 00:04:23,790 --> 00:04:27,890 So 'with_name' will contain "Hello comma Bob." 98 98 00:04:27,890 --> 00:04:30,981 If we print that out, you'll see what I mean. 99 99 00:04:30,981 --> 00:04:33,900 line:15% You get Hello, Bob printed out. 100 100 00:04:33,900 --> 00:04:37,750 One of the benefits of this is that you can then 101 101 00:04:37,750 --> 00:04:40,830 use this 'with_name' with other things, 102 102 00:04:40,830 --> 00:04:43,569 so you can reuse the template, the greeting, 103 103 00:04:43,569 --> 00:04:46,464 and instead pass in Rolf, for example, 104 104 00:04:46,464 --> 00:04:49,500 line:15% and then if you run this, you'll get Hello, Rolf. 105 105 00:04:49,500 --> 00:04:51,910 So it allows you to define a template 106 106 00:04:51,910 --> 00:04:54,630 that you can reuse with multiple values. 107 107 00:04:54,630 --> 00:04:58,530 Notice that in here you can have one with Bob there, 108 108 00:04:58,530 --> 00:05:00,560 then you can have one with Rolf 109 109 00:05:02,407 --> 00:05:05,360 and you can do that everywhere then. 110 110 00:05:07,860 --> 00:05:10,100 line:15% So now you have reused the template two times 111 111 00:05:10,100 --> 00:05:12,180 line:15% to create two different strings. 112 112 00:05:12,180 --> 00:05:15,540 This is why the format can be useful 113 113 00:05:15,540 --> 00:05:17,750 instead of F strings, but generally, 114 114 00:05:17,750 --> 00:05:19,990 you'll be using F strings 115 115 00:05:19,990 --> 00:05:22,233 if you're using Python 3.6 or later. 116 116 00:05:23,980 --> 00:05:26,550 Another benefit of using format 117 117 00:05:26,550 --> 00:05:29,140 is that you can create longer templates. 118 118 00:05:29,140 --> 00:05:30,920 For example, here we've got a longer phrase 119 119 00:05:30,920 --> 00:05:33,235 that says Hello comma placeholder. 120 120 00:05:33,235 --> 00:05:35,450 Today is placeholder. 121 121 00:05:35,450 --> 00:05:37,692 So we can say longer_phrase.format 122 122 00:05:37,692 --> 00:05:40,900 and then we can pass in Rolf and Monday. 123 123 00:05:40,900 --> 00:05:42,870 What this will do is it will put the values 124 124 00:05:42,870 --> 00:05:45,300 Rolf and Monday into the placeholders 125 125 00:05:45,300 --> 00:05:47,724 one at a time, so Rolf will go into the first placeholder, 126 126 00:05:47,724 --> 00:05:50,063 Monday will go into the second placeholder, 127 127 00:05:50,063 --> 00:05:51,802 and then you can print this out, 128 128 00:05:51,802 --> 00:05:55,610 line:15% and you will get back the appropriate value, 129 129 00:05:55,610 --> 00:05:57,323 line:15% Hello, Rolf. Today is Monday. 130 130 00:05:58,180 --> 00:06:00,478 Again, you could do this with many different strings, 131 131 00:06:00,478 --> 00:06:02,960 so that is something that is available 132 132 00:06:02,960 --> 00:06:04,160 if you'd like to use it, 133 133 00:06:04,160 --> 00:06:06,840 but generally you'll be using F strings. 134 134 00:06:06,840 --> 00:06:08,300 Those are the two main ways of 135 135 00:06:08,300 --> 00:06:10,840 doing string formatting in Python, 136 136 00:06:10,840 --> 00:06:14,822 which means, essentially, to embed values inside a string. 137 137 00:06:14,822 --> 00:06:17,100 There are other ways which are older, 138 138 00:06:17,100 --> 00:06:19,890 but we're not gonna be learning about those in these videos, 139 139 00:06:19,890 --> 00:06:22,713 just because they're not really used all that much anymore. 140 140 00:06:22,713 --> 00:06:24,400 Thanks for joining me in this video 141 141 00:06:24,400 --> 00:06:26,013 and I'll see you in the next one.