1 00:00:04,570 --> 00:00:08,680 When printing strings and numbers, it would often be convenient to display 2 00:00:45,700 --> 00:00:51,780 So let's swing over to the code and create a new file. 3 00:00:51,780 --> 00:00:57,760 I'm going to call this one repfields. 4 00:00:57,760 --> 00:01:03,360 Alright, so I'm going to start by typing age equals 24, then on line 2 we're going to do print parentheses 5 00:01:03,360 --> 00:01:13,400 double quotes, my age is, space double quote + str age in parentheses + 6 00:01:13,400 --> 00:01:19,120 double quotes space years, closing double quote and right parenthesis. 7 00:01:19,120 --> 00:01:25,840 So if we run the program, we confirm we get the output, my age is 24 years, and no longer 8 00:01:25,840 --> 00:01:30,040 getting an error now, when we're using the plus operator to concatenate numbers 9 00:01:30,040 --> 00:01:37,480 and strings. So using the string function helps us to, basically, coerce an integer 10 00:01:37,480 --> 00:01:41,830 into a string, but this can rapidly become tedious; having to coerce every 11 00:01:41,830 --> 00:01:46,270 variable using the string function. Python 3 provides a much better 12 00:01:46,270 --> 00:01:53,320 mechanism, and that has improved further in Python 3.6. So python 3 allows strings 13 00:01:53,320 --> 00:01:59,380 to be formatted using replacement fields and the dot format method. And these are 14 00:01:59,380 --> 00:02:04,200 probably best explained with a few examples. So let's change line 2, 15 00:02:04,200 --> 00:02:09,139 instead of using the string function, I'm going to put my age is, and I'm going 16 00:02:09,139 --> 00:02:13,100 to put left and right curly braces before the closing double quote, 17 00:02:13,100 --> 00:02:16,120 with a zero in between them. 18 00:02:16,120 --> 00:02:19,640 So my age is, space left and right curly braces, 19 00:02:19,640 --> 00:02:25,420 zero between that and a space years. I'm going to delete all the code up until the right 20 00:02:25,420 --> 00:02:33,940 parenthesis, and replace outside the double quote with dot format age in parentheses. 21 00:02:33,940 --> 00:02:37,090 So this will produce the same output as the previous example, 22 00:02:37,090 --> 00:02:41,320 but without having to coerce the number into a string. So let's just run this 23 00:02:41,320 --> 00:02:46,720 to confirm that it works. We get the same output; my age is 24 years. 24 00:02:46,720 --> 00:02:51,780 So the replacement field is represented by the left curly brace the 0 and the right 25 00:02:51,790 --> 00:02:56,680 curly brace, which is then replaced by the first value in the format list, 26 00:02:56,680 --> 00:02:59,590 age in this case. And at the moment we've only got the one value in there and 27 00:02:59,590 --> 00:03:03,519 that's the variable age. So that doesn't look like much of an improvement over 28 00:03:03,520 --> 00:03:09,880 the previous code, but consider this one instead; so I'm going to type it out. 29 00:03:09,880 --> 00:03:16,140 Line 4, I'm going to type print parentheses and double quotes, there are, and we'll add 30 00:03:16,150 --> 00:03:19,930 some replacement fields. So first one I'm going to do is a zero and get all of 31 00:03:19,930 --> 00:03:26,000 these in curly braces, There are zero days in, then a curly brace again, 1 32 00:03:26,000 --> 00:03:31,720 with curly braces comma, and we'll do the same for 2, 3, 4, 5, 6 and 7. 33 00:03:31,720 --> 00:03:41,940 2, 3. 4, 5, and you can see I'm putting commas and putting curly 34 00:03:41,940 --> 00:03:45,360 braces around these numbers again, 6 and we'll finish off the last one. 35 00:03:45,360 --> 00:03:49,320 We'll put and, replacement field 7. 36 00:03:49,320 --> 00:03:52,300 So I'm going to do that, then press enter there. 37 00:03:52,300 --> 00:03:58,520 On the next line, type dot format, then another set of parentheses, 38 00:03:58,520 --> 00:04:04,880 and I'm going to type 31 comma in the left parenthesis, well after the left parenthesis 39 00:04:04,880 --> 00:04:09,880 Jan, March, or M a r, the abbreviations I'm going to use here, 40 00:04:09,880 --> 00:04:15,500 May, oops, I missed a double quote there. 41 00:04:16,459 --> 00:04:26,760 July, August, October, and the last one, December. 42 00:04:26,770 --> 00:04:31,630 Then a closing parentheses. So I've split that code over two lines, which is something 43 00:04:31,630 --> 00:04:36,220 you'll see done a lot in Python. Long lines are actually frowned upon in the 44 00:04:36,220 --> 00:04:40,000 Python style guide, which we'll talk more about later. For now, just know that 45 00:04:40,000 --> 00:04:43,800 Python allows you to split your lines of code like I've just done. 46 00:04:43,800 --> 00:04:48,700 Alright, so the replacement fields are replaced by the values that appear in the dot format 47 00:04:48,700 --> 00:04:53,710 method call, with the first value replacing 0, the second replacing 1 and 48 00:04:53,710 --> 00:04:56,710 so on. So you can see there, we've actually got a total of 7 replacement fields 49 00:04:56,710 --> 00:04:59,950 defined on line 4, and each of those values are going to go into the 50 00:04:59,950 --> 00:05:06,280 respective number, 0 through 7. So we've got a total of 8 items in the list after 51 00:05:06,280 --> 00:05:10,630 the dot format, and each of those will go into the replacement fields numbered 0 52 00:05:10,630 --> 00:05:17,900 through 7 in our string. So if we run the program now, 53 00:05:17,920 --> 00:05:19,500 and comparing the output at 54 00:05:19,510 --> 00:05:23,350 the bottom of the screen with the values that appear inside the parentheses 55 00:05:23,350 --> 00:05:26,880 after the dot format method call. 56 00:05:56,300 --> 00:05:58,900 Of course, you probably wouldn't use string literals 57 00:05:58,900 --> 00:06:02,640 inside format, because of course they can just be included in the string. 58 00:06:02,640 --> 00:06:07,280 So we could have, in this case, replaced what we did there, with something that's probably a 59 00:06:07,280 --> 00:06:20,260 lot more readable; print There are, replacement field 0 days in, in Jan, 60 00:06:20,260 --> 00:06:32,420 March, May, July, August, October and December and dot format. 61 00:06:32,420 --> 00:06:38,120 So that does exactly the same thing, but I just wanted to demonstrate that you can have multiple replacement fields 62 00:06:38,120 --> 00:06:41,930 inside a string, and we'll just run that to confirm, and I probably should have 63 00:06:41,930 --> 00:06:48,720 written it like that, and to be consistent, run it again and we've got the identical output. 64 00:06:48,720 --> 00:06:52,040 The other thing to keep in mind is that fields can be used more than once, 65 00:06:52,040 --> 00:06:55,970 and they don't have to appear in the order that the values are provided to the dot 66 00:06:55,970 --> 00:06:59,300 format method call. It's the field index, the number inside 67 00:06:59,300 --> 00:07:03,480 the curly braces, that determines which value to be used. 68 00:07:03,480 --> 00:07:07,120 So here's an example to demonstrate that. 69 00:07:07,120 --> 00:07:13,040 So I'm gonna come down here on line 8, print parentheses, 70 00:07:13,040 --> 00:07:15,780 I'm gonna start with a double quote Jan: 71 00:07:15,780 --> 00:07:27,060 I'm gonna start with replacement field 2, then Feb: 0 replacement field, Mar: 72 00:07:27,060 --> 00:07:38,680 I'm gonna use 2 again, Apr: with replacement field 1, May: 2, Jun: 1, 73 00:07:38,680 --> 00:07:54,420 replacement field 1, Jul: replacement field 2, Sep: 1 and Oct: 2, 74 00:07:54,420 --> 00:08:03,720 replacement field 2, two more, Nov: replacement field 1 comma Dec: replacement field 2. 75 00:08:03,720 --> 00:08:05,800 and obviously, I've got a large font here so we're not gonna be able to 76 00:08:05,810 --> 00:08:10,400 see the entire contents on that line, on this one line. So what I'm going to do is 77 00:08:10,400 --> 00:08:16,400 actually go to the end there, press enter there, dot format, and I'm going to put 78 00:08:16,400 --> 00:08:20,880 three values; 28, 30 and 31. 79 00:08:20,880 --> 00:08:25,460 So if we run the program, and you can see now that 80 00:08:25,460 --> 00:08:30,950 wherever there's a replacement field 0, it's replaced with the first value in 81 00:08:30,950 --> 00:08:35,900 the list, 28. We've only got replacement field 0 once for February, 82 00:08:35,900 --> 00:08:40,440 and all the replacement field 1 fields are replaced with the second value, which is 30, 83 00:08:40,440 --> 00:08:46,980 and the third value, 31, is used to replace all the replacement field 2 replacement fields. 84 00:08:46,980 --> 00:08:50,120 Now you can also use triple quotes. What I'll do is I'll print 85 00:08:50,120 --> 00:08:56,540 a blank line first, and close this run window down. We'll just print an empty line, 86 00:08:56,540 --> 00:09:01,180 and we can also do something similar using triple quotes. So I could do print 87 00:09:01,180 --> 00:09:05,040 parentheses three quotes, triple quotes in other words, 88 00:09:05,040 --> 00:09:09,520 press ENTER there. Then what I'm going to do is take a copy of this entire line, 89 00:09:09,520 --> 00:09:15,440 just save me typing it again. Okay, take a copy of that. I'm going to go back and 90 00:09:15,440 --> 00:09:20,360 paste it after the triple quotes. Then what I'm going to do is just press ENTER 91 00:09:20,360 --> 00:09:24,050 after each one to make it a bit more readable, and because I'm pressing enter 92 00:09:24,050 --> 00:09:26,920 on a separate line now, I'm also going to remove the double quotes, 93 00:09:26,920 --> 00:09:34,860 remove the comma rather. So we've got February, March. 94 00:09:44,420 --> 00:09:48,480 That's the end of the line now, so I'm going to add the three closing double quotes there, 95 00:09:48,480 --> 00:09:51,860 and I'm just going to put our format statement after that, dot format 96 00:09:51,860 --> 00:10:02,280 parenthesis 28, 30, 31, like so. So now if we run that, 97 00:10:02,280 --> 00:10:06,860 I'm looking at the output for this program. Each month is appearing on a new line and the 98 00:10:06,860 --> 00:10:11,040 number of days is also showing on there as well. So that, I'm sure we agree, would be very 99 00:10:11,040 --> 00:10:14,720 difficult, or would be very messy, to reproduce with string concatenation. 100 00:10:14,720 --> 00:10:19,500 So the actual replacement is pretty easy to work out. 101 00:10:22,480 --> 00:10:27,180 So replacement field zero is replaced with 28, and you can see the example there, 102 00:10:27,180 --> 00:10:31,540 showing us on line 14. So it's automatically coerced to be a string for us. 103 00:10:31,540 --> 00:10:37,060 Replacement field 1 is replaced by 30. We've defined that as the second entry 104 00:10:37,060 --> 00:10:41,440 in our format list there, and replacement field 2 is replaced by 31. 105 00:10:41,440 --> 00:10:45,060 You can see, obviously, the same use of the replacement fields in the code 106 00:10:45,060 --> 00:10:49,060 and we can see the output showing down the bottom of the screen. Now if we'd used 107 00:10:49,060 --> 00:10:52,870 replacement field 3 in the string, then we'd have to produce, or provide rather, 108 00:10:52,870 --> 00:10:57,880 another value in the dot format method call. Alright so make sure you understand 109 00:10:57,880 --> 00:11:03,600 how the replacement fields are being used before moving on to the next video.