WEBVTT 1 00:00:01.180 --> 00:00:02.680 Hi guys and welcome back. 2 00:00:02.680 --> 00:00:04.220 In this video, we're going to talk about 3 00:00:04.220 --> 00:00:06.623 string formatting in Python. 4 00:00:07.480 --> 00:00:08.940 Specifically, we're going to be using 5 00:00:08.940 --> 00:00:13.340 a newer Python feature from Python 3.6 onwards. 6 00:00:13.340 --> 00:00:14.410 So for this video, 7 00:00:14.410 --> 00:00:18.590 make sure that you're using Python 3.6 or later. 8 00:00:18.590 --> 00:00:20.427 Let's say that you've got two strings, 9 00:00:20.427 --> 00:00:24.269 one, which is Bob, and has the name of 'name,' 10 00:00:24.269 --> 00:00:26.010 and one which is Hello, Bob and has the name of 'greeting.' 11 00:00:28.610 --> 00:00:30.964 If you print greeting out, of course 12 00:00:30.964 --> 00:00:32.796 line:15% you're going to get, 13 00:00:32.796 --> 00:00:37.420 line:15% Hello Bob, since that are the contents of the string. 14 00:00:37.420 --> 00:00:40.528 But if you set 'name' to Rolf 15 00:00:40.528 --> 00:00:43.380 and then you print greeting again, 16 00:00:43.380 --> 00:00:45.500 then naturally as you run that, 17 00:00:45.500 --> 00:00:49.420 line:15% you're gonna get Hello, Bob and then Hello, Bob again. 18 00:00:49.420 --> 00:00:53.950 Greeting contains the string name, which is Bob, 19 00:00:53.950 --> 00:00:57.320 but it doesn't calculate it dynamically, 20 00:00:57.320 --> 00:00:59.900 which means that when greeting is defined, 21 00:00:59.900 --> 00:01:04.900 it contains the characters Hello comma space Bob. 22 00:01:05.020 --> 00:01:07.970 And then changing 'name' doesn't change that greeting. 23 00:01:07.970 --> 00:01:10.550 So if you wanted to change the greeting, 24 00:01:10.550 --> 00:01:13.250 you would have to do something a little bit different. 25 00:01:15.160 --> 00:01:18.403 Indeed, instead of typing, Hello comma Bob, 26 00:01:18.403 --> 00:01:20.444 what you'd like to do is to put an 'F' 27 00:01:20.444 --> 00:01:22.980 in front of the quotation marks. 28 00:01:22.980 --> 00:01:26.610 So now we've got what's called an F string in Python. 29 00:01:26.610 --> 00:01:29.810 An F string allows us to embed variables 30 00:01:29.810 --> 00:01:31.560 inside of strings. 31 00:01:31.560 --> 00:01:33.700 So here instead of Hello comma Bob, 32 00:01:33.700 --> 00:01:38.700 we can do Hello comma 'name' inside these curly braces. 33 00:01:38.960 --> 00:01:42.249 Now, again, we've got F and then inside the string, 34 00:01:42.249 --> 00:01:46.200 we can use the curly braces and inside the curly braces, 35 00:01:46.200 --> 00:01:48.850 we can put a variable name. 36 00:01:48.850 --> 00:01:52.090 So when this is calculated, 37 00:01:52.090 --> 00:01:55.190 'name' will be replaced by Bob, 38 00:01:55.190 --> 00:01:57.830 so we will print out Hello, Bob. 39 00:01:57.830 --> 00:01:58.940 So if we run that, 40 00:01:58.940 --> 00:02:01.780 line:15% you'll see down here that we get Hello, Bob. 41 00:02:01.780 --> 00:02:04.640 So exactly the same thing as before. 42 00:02:04.640 --> 00:02:06.820 At this point, I'll say that if you do 43 00:02:06.820 --> 00:02:10.034 what we had earlier and set 'name' to Rolf, 44 00:02:10.034 --> 00:02:11.830 and then you print greeting again, 45 00:02:11.830 --> 00:02:14.440 you'll have the same problem as before. 46 00:02:14.440 --> 00:02:15.920 line:15% So if you press play again, 47 00:02:15.920 --> 00:02:18.100 line:15% you'll see Hello, Bob, Hello, Bob. 48 00:02:18.100 --> 00:02:21.250 So what we've done here is we have embedded 49 00:02:21.250 --> 00:02:24.160 the variable inside the string 50 00:02:24.160 --> 00:02:26.540 with the value that that variable had 51 00:02:26.540 --> 00:02:28.630 at this point in time, in line 2. 52 00:02:28.630 --> 00:02:31.280 So in line 2, 'name' had the value of Bob, 53 00:02:31.280 --> 00:02:33.343 so greeting is Hello, Bob. 54 00:02:34.410 --> 00:02:36.640 So what is the point of using the F string 55 00:02:36.640 --> 00:02:38.930 if it doesn't change dynamically? 56 00:02:38.930 --> 00:02:40.470 Well, the good thing about this F string 57 00:02:40.470 --> 00:02:42.940 is that instead of defining a variable for it, 58 00:02:42.940 --> 00:02:46.190 if you wanted to have a different value each time, 59 00:02:46.190 --> 00:02:48.713 you could just print it out, like that, 60 00:02:48.713 --> 00:02:51.716 and get rid of this variable definition. 61 00:02:51.716 --> 00:02:54.740 Now what we've got here is we are printing 62 00:02:54.740 --> 00:02:56.590 and inside the brackets, we've got 63 00:02:56.590 --> 00:02:58.060 the value that we want to print, 64 00:02:58.060 --> 00:02:59.485 so here we have the F string, 65 00:02:59.485 --> 00:03:02.300 which includes an F, then the quotation marks, 66 00:03:02.300 --> 00:03:04.725 and then the characters inside it, including the variable. 67 00:03:04.725 --> 00:03:06.512 By doing something like this, 68 00:03:06.512 --> 00:03:08.578 now every time you run this code, 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 00:03:12.100 --> 00:03:15.113 line:15% so we get Hello, Bob, and Hello, Rolf. 71 00:03:17.060 --> 00:03:19.154 There is a way of defining a template, 72 00:03:19.154 --> 00:03:22.120 which instead of calculating it at 73 00:03:22.120 --> 00:03:23.860 the time where it is defined, 74 00:03:23.860 --> 00:03:25.330 you can calculate the values 75 00:03:25.330 --> 00:03:27.470 to be replaced inside it later on. 76 00:03:27.470 --> 00:03:28.950 Here's how you do that. 77 00:03:28.950 --> 00:03:31.738 So you can define your greeting as 'Hello,' 78 00:03:31.738 --> 00:03:34.620 and then open and closing curly braces. 79 00:03:34.620 --> 00:03:37.710 Notice that we don't have an F in front of it. 80 00:03:37.710 --> 00:03:39.890 Then you can say that with 'name,' 81 00:03:39.890 --> 00:03:41.250 which is another variable, 82 00:03:41.250 --> 00:03:45.728 is greeting.format and then 'name.' 83 00:03:45.728 --> 00:03:47.240 So what we've done here 84 00:03:47.240 --> 00:03:49.722 is we have created now three strings. 85 00:03:49.722 --> 00:03:52.560 We have the string 'name,' which has the value Bob, 86 00:03:52.560 --> 00:03:54.900 we have the string 'greeting,' which is our template, 87 00:03:54.900 --> 00:03:57.584 which says, "Hello comma curly braces 88 00:03:57.584 --> 00:04:01.690 and finally we say, greeting.format 89 00:04:01.690 --> 00:04:05.190 and then inside brackets, we put in the name. 90 00:04:05.190 --> 00:04:07.056 So what this is doing is essentially it's calling 91 00:04:07.056 --> 00:04:09.640 the format function 92 00:04:09.640 --> 00:04:13.320 inside of 'greeting' and what that's doing is, 93 00:04:13.320 --> 00:04:16.730 it is giving the name to this template, 94 00:04:16.730 --> 00:04:19.400 and what the template will do is it will 95 00:04:19.400 --> 00:04:20.810 replace the curly braces 96 00:04:20.810 --> 00:04:23.790 by the contents of the 'name' variable. 97 00:04:23.790 --> 00:04:27.890 So 'with_name' will contain "Hello comma Bob." 98 00:04:27.890 --> 00:04:30.981 If we print that out, you'll see what I mean. 99 00:04:30.981 --> 00:04:33.900 line:15% You get Hello, Bob printed out. 100 00:04:33.900 --> 00:04:37.750 One of the benefits of this is that you can then 101 00:04:37.750 --> 00:04:40.830 use this 'with_name' with other things, 102 00:04:40.830 --> 00:04:43.569 so you can reuse the template, the greeting, 103 00:04:43.569 --> 00:04:46.464 and instead pass in Rolf, for example, 104 00:04:46.464 --> 00:04:49.500 line:15% and then if you run this, you'll get Hello, Rolf. 105 00:04:49.500 --> 00:04:51.910 So it allows you to define a template 106 00:04:51.910 --> 00:04:54.630 that you can reuse with multiple values. 107 00:04:54.630 --> 00:04:58.530 Notice that in here you can have one with Bob there, 108 00:04:58.530 --> 00:05:00.560 then you can have one with Rolf 109 00:05:02.407 --> 00:05:05.360 and you can do that everywhere then. 110 00:05:07.860 --> 00:05:10.100 line:15% So now you have reused the template two times 111 00:05:10.100 --> 00:05:12.180 line:15% to create two different strings. 112 00:05:12.180 --> 00:05:15.540 This is why the format can be useful 113 00:05:15.540 --> 00:05:17.750 instead of F strings, but generally, 114 00:05:17.750 --> 00:05:19.990 you'll be using F strings 115 00:05:19.990 --> 00:05:22.233 if you're using Python 3.6 or later. 116 00:05:23.980 --> 00:05:26.550 Another benefit of using format 117 00:05:26.550 --> 00:05:29.140 is that you can create longer templates. 118 00:05:29.140 --> 00:05:30.920 For example, here we've got a longer phrase 119 00:05:30.920 --> 00:05:33.235 that says Hello comma placeholder. 120 00:05:33.235 --> 00:05:35.450 Today is placeholder. 121 00:05:35.450 --> 00:05:37.692 So we can say longer_phrase.format 122 00:05:37.692 --> 00:05:40.900 and then we can pass in Rolf and Monday. 123 00:05:40.900 --> 00:05:42.870 What this will do is it will put the values 124 00:05:42.870 --> 00:05:45.300 Rolf and Monday into the placeholders 125 00:05:45.300 --> 00:05:47.724 one at a time, so Rolf will go into the first placeholder, 126 00:05:47.724 --> 00:05:50.063 Monday will go into the second placeholder, 127 00:05:50.063 --> 00:05:51.802 and then you can print this out, 128 00:05:51.802 --> 00:05:55.610 line:15% and you will get back the appropriate value, 129 00:05:55.610 --> 00:05:57.323 line:15% Hello, Rolf. Today is Monday. 130 00:05:58.180 --> 00:06:00.478 Again, you could do this with many different strings, 131 00:06:00.478 --> 00:06:02.960 so that is something that is available 132 00:06:02.960 --> 00:06:04.160 if you'd like to use it, 133 00:06:04.160 --> 00:06:06.840 but generally you'll be using F strings. 134 00:06:06.840 --> 00:06:08.300 Those are the two main ways of 135 00:06:08.300 --> 00:06:10.840 doing string formatting in Python, 136 00:06:10.840 --> 00:06:14.822 which means, essentially, to embed values inside a string. 137 00:06:14.822 --> 00:06:17.100 There are other ways which are older, 138 00:06:17.100 --> 00:06:19.890 but we're not gonna be learning about those in these videos, 139 00:06:19.890 --> 00:06:22.713 just because they're not really used all that much anymore. 140 00:06:22.713 --> 00:06:24.400 Thanks for joining me in this video 141 00:06:24.400 --> 00:06:26.013 and I'll see you in the next one.