1 00:00:04,190 --> 00:00:09,660 So string replacement fields can also contain formatting, to display values 2 00:00:09,660 --> 00:00:13,200 with a specific number of decimal places, for example. 3 00:00:13,200 --> 00:00:17,100 So let's create a new Python file. I'm going to call it formatting, 4 00:00:23,020 --> 00:00:27,140 and I'm going to use a for loop to generate some output. 5 00:00:27,140 --> 00:00:30,980 We'll be looking at for loops in the next section, so don't worry about what's happening. 6 00:00:30,980 --> 00:00:34,040 Concentrate on the print lines that I'm going to type in this code, to see 7 00:00:34,040 --> 00:00:37,940 the effect of the formatting in the replacement fields. So we're going to 8 00:00:37,940 --> 00:00:43,200 start by printing the values from 1 to 12, with the values of their squares and cubes. 9 00:00:43,200 --> 00:00:50,560 So on line 1 I'm going to type for i in range(1, 13): 10 00:00:50,560 --> 00:00:55,079 and put a colon to the right of the right parenthesis. So on line 2 I'm 11 00:00:55,079 --> 00:00:59,850 going to press ENTER here. You need to make sure there's 4 spaces before print, 12 00:00:59,850 --> 00:01:05,420 which I'm about to type, on line 2. I'm going to type print parentheses, 13 00:01:05,420 --> 00:01:09,780 and in double quotes I'm going to type number, or the abbreviation No, period. Then I'm 14 00:01:09,780 --> 00:01:13,200 going to put replacement field 0, which is our left and right curly braces with a 15 00:01:13,200 --> 00:01:25,920 0 in the middle, squared is, and replacement field 1, and cubed is, replacement field 2. 16 00:01:25,920 --> 00:01:31,680 Then I'm going to type dot format parentheses i, i. I'm going to use 17 00:01:31,680 --> 00:01:37,920 the exponent operator, which is 2 multiplication signs, 2 then i, exponent 18 00:01:37,920 --> 00:01:42,030 operator again, 3, which is to the power. It's basically raising one number 19 00:01:42,030 --> 00:01:44,340 to the power of another in Python. 20 00:01:44,340 --> 00:01:50,960 Alright so if we run this now, 21 00:01:50,960 --> 00:01:55,140 and you can see we've got the values of the number, the value squared, and the value 22 00:01:55,140 --> 00:01:59,520 cubed, for each of those numbers. And in case it's not obvious now, you can 23 00:01:59,520 --> 00:02:04,200 provide any expressions inside the format parentheses. They don't have to be 24 00:02:04,200 --> 00:02:09,720 variables or literal numbers. On line 2, we've got i exponent operator 2 to get 25 00:02:09,720 --> 00:02:14,520 the number squared, and i exponent operator 3 to get the number cubed. 26 00:02:14,520 --> 00:02:17,700 And the exponent operator, is how you can raise one 27 00:02:17,700 --> 00:02:22,020 number to the power of another in Python. So that's the power to operator as well. 28 00:02:22,020 --> 00:02:25,700 Alright so that works, but as you can see, the numbers aren't - or the 29 00:02:25,709 --> 00:02:29,790 values rather - aren't lined up. So we can fix that in the output, or we'll fix the 30 00:02:29,790 --> 00:02:34,050 output by applying some formatting. So firstly, I'm going to specify a field width 31 00:02:34,050 --> 00:02:38,310 for each of the replacement fields. So all the values for i are a maximum of 32 00:02:38,310 --> 00:02:42,120 two digits, because we're, obviously, only counting from 1 to 12 here. So we can use a 33 00:02:42,120 --> 00:02:44,700 field width of 2 for the first replacement field. 34 00:02:44,700 --> 00:02:48,930 I'm going to use a field width of 4 for the other two fields. So to actually 35 00:02:48,930 --> 00:02:53,910 specify width, we come back up to our line 2, and we add the width by putting a 36 00:02:53,910 --> 00:02:57,090 colon and then the number that we need. So for the first replacement field 37 00:02:57,090 --> 00:03:01,860 zero, I'm going to put :2 there, for a width of 2, and for the other two 38 00:03:01,860 --> 00:03:13,010 replacement fields I'm going to put :4 and :4 again. So if we run the program now, 39 00:03:14,080 --> 00:03:18,970 it's now easier to understand, because the formatting makes it easier to see at a 40 00:03:18,970 --> 00:03:22,480 glance, what the values are. Alright so that looks tidier. The values are now 41 00:03:22,480 --> 00:03:27,610 lining up nicely. So on line 2, we're using 0:2 in 42 00:03:27,610 --> 00:03:30,420 our left and right curly braces for the first replacement field. 43 00:03:30,420 --> 00:03:35,780 2 is the field width, as I mentioned, and it's separated from the index with a colon. 44 00:03:35,780 --> 00:03:38,920 Now everything in that first column prints in a width of two 45 00:03:38,920 --> 00:03:43,040 characters. So think of it as reserving two spaces on the screen, 46 00:03:43,040 --> 00:03:46,960 so that the one digit values still line up with the two digit ones, and you can see 47 00:03:46,960 --> 00:03:50,710 they're happening there in the output. Now our squares also line up, in a field 48 00:03:50,710 --> 00:03:54,490 width of four characters. Maybe a width of three would look better there; have 49 00:03:54,490 --> 00:03:57,370 a got at changing that yourself, and see what it looks like. Pause the video 50 00:03:57,370 --> 00:04:01,260 and I'll make the change when you come back. 51 00:04:01,490 --> 00:04:05,480 Okay, so if we only want to use three spaces for the square values, the change is 52 00:04:05,480 --> 00:04:09,530 obviously easy enough. We come back up to replacement field 1, change the 4 to 53 00:04:09,530 --> 00:04:15,950 a 3, and if we run it again, well that looks tidier still now, as 54 00:04:15,950 --> 00:04:20,750 you can see. There's now only one space between is and the value on the last 55 00:04:20,750 --> 00:04:25,610 three rows. We can also align the values in their field width. To left align the 56 00:04:25,610 --> 00:04:30,410 values we place a < symbol after the colon. So what I'm going to do is, 57 00:04:30,410 --> 00:04:36,290 just to make this easier to see, I'm going to firstly add a blank line. Then I'm 58 00:04:36,290 --> 00:04:40,670 going to take a copy of the line - of the two lines there. We'll just run it again 59 00:04:40,670 --> 00:04:45,480 so the original code's there as well. So I'm going to paste that in as it was before. 60 00:04:45,480 --> 00:04:49,440 So this time what I'm going to do, again we're trying to left align the values, 61 00:04:49,440 --> 00:04:53,500 so we'll leave replacement field 0 as it is, the first one. For the second one 62 00:04:53,510 --> 00:04:55,790 we're going to put, before the three, I'm going to put the less than sign there, 63 00:04:55,790 --> 00:05:02,620 and for replacement field 2, we're going to put a less than there as well. 64 00:05:02,620 --> 00:05:06,000 So if we run this, 65 00:05:06,000 --> 00:05:08,960 and the values are now left aligned, and if it's not immediately 66 00:05:08,960 --> 00:05:12,050 clear to you what's going on there, scroll up the output to compare the 67 00:05:12,050 --> 00:05:15,830 two blocks. But if we have a look at the formatting here, notice how it's now left 68 00:05:15,830 --> 00:05:21,360 aligned. If we go back up to the top, you can see clearly that was right aligned. 69 00:05:21,360 --> 00:05:26,020 So the alignment symbols are quite visual. The less than, left aligns, 70 00:05:26,020 --> 00:05:30,640 the greater than will right align, and a caret symbol, well that centers within the 71 00:05:30,640 --> 00:05:34,440 field width. So let's center the last column to see what that looks like. 72 00:05:34,440 --> 00:05:38,240 So instead of using the less than there, I'm going to change that by using the caret 73 00:05:38,240 --> 00:05:43,960 symbol instead. And if you run this code again, 74 00:05:43,960 --> 00:05:48,620 you can see the values are now clearly centered, compared to the first output, 75 00:05:48,620 --> 00:05:50,900 which was right justified on the right hand side 76 00:05:50,900 --> 00:05:53,900 and this is obviously for the cubed values. 77 00:05:53,900 --> 00:05:57,650 Now keep in mind that we don't get half spacing in a terminal, so the result 78 00:05:57,650 --> 00:06:02,800 isn't as accurate as centering values in a GUI program, but it's available if you want it. 79 00:06:02,800 --> 00:06:06,800 So for floating-point numbers you can specify a precision - the number 80 00:06:06,800 --> 00:06:11,480 of digits after the decimal point. For our precision, we specify the precision 81 00:06:11,480 --> 00:06:14,960 after a decimal point, following the width. 82 00:06:14,960 --> 00:06:19,180 So let's have a go at doing that, so I'm going to type some more code in. 83 00:06:19,180 --> 00:06:21,620 So I'm going to put an empty line in there, 84 00:06:21,620 --> 00:06:24,660 and the line after, well actually line 11, I'm going to type print 85 00:06:24,660 --> 00:06:30,580 parentheses Pi is approximately, 86 00:06:30,580 --> 00:06:34,980 we're going to put replacement field 0:12, 87 00:06:34,980 --> 00:06:41,020 which is the precision for a floating-point number, then dot format 88 00:06:41,020 --> 00:06:47,599 parentheses 22 divided by 7, and 2 right parentheses to close it off. And let's take a copy of 89 00:06:47,600 --> 00:06:52,680 that line, we're going to make some modifications. So I need another 5 lines. 90 00:06:52,680 --> 00:06:55,700 I'm going to paste that 5 times. 91 00:06:57,300 --> 00:07:02,860 Alright, so on line 12 what we're going to do, is we're going to put an f after the 12. 92 00:07:02,860 --> 00:07:17,740 Next line, we going to put 12.50f, line 14 we're going to put 0:52.50f, 93 00:07:17,740 --> 00:07:29,340 and the next, I'm going to put 62.50f, and the last line, I'm going to put 72.50f. 94 00:07:29,340 --> 00:07:34,640 So the first line of output, well actually, I'll run it first and then we'll talk about it. 95 00:07:34,640 --> 00:07:38,620 So the first line of output, and that's produced from the code on line 12. 96 00:07:38,620 --> 00:07:42,720 I'm going to see if I can get that on the screen at the same time, on line 11 rather, 97 00:07:42,720 --> 00:07:47,360 well that's the general format, and that defaults to printing 15 decimals. 98 00:07:47,360 --> 00:07:53,020 When we specify a floating-point value using the f on line 12, 99 00:07:53,020 --> 00:07:57,080 we get the default of 6 digits after the decimal point. 100 00:07:57,080 --> 00:08:02,320 Now on lines 13 through 16, we're still specifying a floating-point format, 101 00:08:02,320 --> 00:08:07,620 but we also add a precision of 50 and that gives 50 points after the decimal point. 102 00:08:07,620 --> 00:08:11,920 The third line of output corresponds to line 13. If you think it doesn't look 103 00:08:11,930 --> 00:08:15,409 right that's because Python won't truncate a number. We can't put a value 104 00:08:15,409 --> 00:08:21,319 that's got 50 decimals in a field width of 12. Python decides that precision is 105 00:08:21,319 --> 00:08:25,069 more important than field width, and ignores the value 12 that we've 106 00:08:25,069 --> 00:08:29,210 specified for the width, and that's the code on line 13. 107 00:08:29,210 --> 00:08:32,779 Now the next three lines after that, print the same value but in different 108 00:08:32,779 --> 00:08:36,589 field widths. When we specify width greater than 50, you can see that the 109 00:08:36,589 --> 00:08:40,370 effect becomes clear. Now the maximum precision of a Python floating-point 110 00:08:40,370 --> 00:08:45,260 number is between 51 and 53 digits. There's not much point specifying a 111 00:08:45,260 --> 00:08:48,890 precision greater than that. Now this will be easier to see if I left align, 112 00:08:48,890 --> 00:08:52,459 that last line, so I'm going to do that, and then copy it and increase the 113 00:08:52,459 --> 00:08:59,660 precision just to show you what I mean. I'm going do that, copy that last line 16. 114 00:08:59,660 --> 00:09:07,100 I'm going to change the 72.50f to 72.54f, but we're also going to use the 115 00:09:07,100 --> 00:09:10,380 left align, so you can see the value left aligned, and we'll put that 116 00:09:10,380 --> 00:09:15,780 to the left of the 72 after the colon. We run the program now, 117 00:09:15,780 --> 00:09:16,640 and what I should do is, 118 00:09:16,640 --> 00:09:19,760 actually, left align the previous line as well just so you can see the differences. 119 00:09:19,760 --> 00:09:24,880 So we'll do that again as well on line 16, we'll run that again, 120 00:09:24,880 --> 00:09:28,300 and you can see we only get one extra digit in the output. We can see that there's 121 00:09:28,300 --> 00:09:31,880 four digits here but the remaining digits are just padded with zeros, 122 00:09:31,880 --> 00:09:35,740 so there's no actual value there. Alright so I'll finish this video now by 123 00:09:35,750 --> 00:09:40,040 mentioning that the field number in replacement fields is optional. 124 00:09:40,040 --> 00:09:44,880 If they're not specified, then Python takes the value from the format method in order. 125 00:09:44,880 --> 00:09:48,960 So to see what I mean, I'm gonna take a copy of the code again, 126 00:09:48,960 --> 00:09:54,320 this code up here on line six. I'll take a copy of that again. 127 00:09:54,320 --> 00:09:57,660 I'm gonna paste it down here on line 19, 128 00:09:57,660 --> 00:10:01,160 and I'm going to actually remove everything. So we're just going to put 129 00:10:01,160 --> 00:10:06,600 just a left and right curly brace only, for the three replacement fields, 130 00:10:06,600 --> 00:10:09,320 and actually, what I'll do on the third replacement field, I'll just put a 131 00:10:09,320 --> 00:10:14,000 colon 4 there, so we can see that we're still specifying a width. 132 00:10:14,000 --> 00:10:17,060 If we run this, 133 00:10:17,060 --> 00:10:21,620 we can see that the third field shows that you can still use a colon to control the layout, 134 00:10:21,620 --> 00:10:25,240 even if you haven't specified a field number. All the values in the final 135 00:10:25,250 --> 00:10:29,390 column of output are printing in a field with the 4. Now if you don't provide 136 00:10:29,390 --> 00:10:34,130 field numbers, you can't use a value more than once, nor can you change the order 137 00:10:34,130 --> 00:10:38,029 in which values are used. Now our earlier example, with the number of days in the month, 138 00:10:38,029 --> 00:10:41,260 wouldn't have actually worked without field numbers. 139 00:10:41,260 --> 00:10:45,040 Alright, so experiment with different values for the field widths and precision's, 140 00:10:45,040 --> 00:10:47,040 to see how it affects your output, 141 00:10:47,040 --> 00:10:50,820 and I'll see you in the next video.