1 00:00:00,360 --> 00:00:02,730 In this exercise, you are going to be building 2 00:00:02,730 --> 00:00:05,850 a program that can tell us how many days 3 00:00:05,850 --> 00:00:09,030 there are in any given month for any given year. 4 00:00:09,030 --> 00:00:10,170 In the Input pane, 5 00:00:10,170 --> 00:00:13,023 you'll see the first line we can input any given year 6 00:00:13,023 --> 00:00:16,620 and on the second line we can input any month. 7 00:00:16,620 --> 00:00:18,570 And what your program is going to do, 8 00:00:18,570 --> 00:00:21,330 is it's going to take those years and month 9 00:00:21,330 --> 00:00:24,690 and figure out how many days there are in that month. 10 00:00:24,690 --> 00:00:26,370 So why do we care about the year? 11 00:00:26,370 --> 00:00:29,100 Well, in leap years, on February, 12 00:00:29,100 --> 00:00:32,907 there's actually 29 days instead of the usual 28. 13 00:00:32,907 --> 00:00:36,690 So this is a great chance for us to practice what we learned 14 00:00:36,690 --> 00:00:38,880 about functions with outputs 15 00:00:38,880 --> 00:00:41,910 and also see some code that we're already familiar with, 16 00:00:41,910 --> 00:00:43,290 which is the code that we use 17 00:00:43,290 --> 00:00:46,530 to work out whether if a year is a leap year. 18 00:00:46,530 --> 00:00:47,760 If you look at the starting code, 19 00:00:47,760 --> 00:00:50,130 you'll see that there is a function called is_leap, 20 00:00:50,130 --> 00:00:52,740 which takes an input of "year" 21 00:00:52,740 --> 00:00:54,300 and we've got the code which comes 22 00:00:54,300 --> 00:00:57,720 from the solution code of the leap year exercise. 23 00:00:57,720 --> 00:00:59,010 Now, if you did it differently, 24 00:00:59,010 --> 00:01:01,230 feel free to modify this function, 25 00:01:01,230 --> 00:01:04,560 it is just there to help you get started. 26 00:01:04,560 --> 00:01:05,393 What you want to do, 27 00:01:05,393 --> 00:01:07,920 is instead of printing leap year or not leap year 28 00:01:07,920 --> 00:01:10,830 you want to make this function have a return. 29 00:01:10,830 --> 00:01:13,170 So it should output either "True", 30 00:01:13,170 --> 00:01:17,040 if it is a leap year, or "False" if it's not a leap year. 31 00:01:17,040 --> 00:01:19,410 And then inside the function days_in_month, 32 00:01:19,410 --> 00:01:22,830 you're going to use this is_leap, 33 00:01:22,830 --> 00:01:25,950 to firstly check the inputs 34 00:01:25,950 --> 00:01:27,900 and the inputs are going to be a year 35 00:01:27,900 --> 00:01:31,230 and a month and you're going to create an output 36 00:01:31,230 --> 00:01:34,590 for this function that gives us just in plain text, 37 00:01:34,590 --> 00:01:36,810 the number of days in the month. 38 00:01:36,810 --> 00:01:41,250 Take a look on line 21, where you've got the days_in_month 39 00:01:41,250 --> 00:01:43,710 and then it takes two inputs, 40 00:01:43,710 --> 00:01:46,590 firstly the year, secondly the month. 41 00:01:46,590 --> 00:01:49,140 And you are going to have to make sure that that order 42 00:01:49,140 --> 00:01:53,130 is respected when you modify the function days_in_month. 43 00:01:53,130 --> 00:01:57,030 And essentially, we've got all of the days in a month 44 00:01:57,030 --> 00:02:00,360 organized in a list called month_days 45 00:02:00,360 --> 00:02:03,420 and you are going to work out, is it a leap year? 46 00:02:03,420 --> 00:02:06,810 If not, then we're just going to use the usual standard days 47 00:02:06,810 --> 00:02:09,600 for February and the rest of the year, 48 00:02:09,600 --> 00:02:10,979 but if it is a leap year 49 00:02:10,979 --> 00:02:13,170 and they want to check that it's February, 50 00:02:13,170 --> 00:02:16,110 then we're going give them 29 instead of the usual 28. 51 00:02:16,110 --> 00:02:17,263 That's the theory of it. 52 00:02:17,263 --> 00:02:20,910 Now it's time to struggle and figure it out all on your own. 53 00:02:20,910 --> 00:02:21,903 So give that a go. 54 00:02:28,512 --> 00:02:33,480 The modification to our is_leap function is pretty easy, 55 00:02:33,480 --> 00:02:36,030 if it originally said print is leap year 56 00:02:36,030 --> 00:02:39,690 then we just return "True", otherwise we return "False". 57 00:02:39,690 --> 00:02:42,780 And this is useful because then we can use this function 58 00:02:42,780 --> 00:02:46,410 inside our other function, days_in_month. 59 00:02:46,410 --> 00:02:48,210 And you know that we can call a function 60 00:02:48,210 --> 00:02:50,100 from within another function. 61 00:02:50,100 --> 00:02:51,150 It's setting us up 62 00:02:51,150 --> 00:02:54,540 to help us when we write our days_in_month function. 63 00:02:54,540 --> 00:02:56,310 Now the first part that we need to modify 64 00:02:56,310 --> 00:03:01,310 for this days_in_month function, is the input parameters. 65 00:03:01,590 --> 00:03:05,400 Notice how on line 22, where we've got the days and month 66 00:03:05,400 --> 00:03:08,790 calling that function, we provide first the year, 67 00:03:08,790 --> 00:03:09,623 then the month. 68 00:03:09,623 --> 00:03:13,110 So we should respect that when we are writing our function, 69 00:03:13,110 --> 00:03:16,800 so that it actually matches the inputs. 70 00:03:16,800 --> 00:03:20,070 The way that we define a function with inputs is "def", 71 00:03:20,070 --> 00:03:21,690 the name of the function, and then 72 00:03:21,690 --> 00:03:25,833 inside the parentheses, the names of the input parameters. 73 00:03:27,330 --> 00:03:32,250 Next, we're going to check if the month that is coming in 74 00:03:32,250 --> 00:03:36,000 through the input for this function is equal to 2 75 00:03:36,000 --> 00:03:40,710 and if we pass the year that's being put into the function, 76 00:03:40,710 --> 00:03:43,350 happens to go through that is_leap function 77 00:03:43,350 --> 00:03:45,600 and come out as True. 78 00:03:45,600 --> 00:03:47,910 So if both of these conditions are True, 79 00:03:47,910 --> 00:03:51,660 then it means the user is checking for a leap year 80 00:03:51,660 --> 00:03:54,600 and they want to know the number of days in February, 81 00:03:54,600 --> 00:03:57,840 in which case we return 29 days. 82 00:03:57,840 --> 00:04:02,460 You have to imagine that on line 15 after the and, 83 00:04:02,460 --> 00:04:06,600 what happens is the input comes in on line 13, 84 00:04:06,600 --> 00:04:09,210 the year, and then we take that year 85 00:04:09,210 --> 00:04:13,980 and we pass it into the is_leap function on line 15, 86 00:04:13,980 --> 00:04:15,990 it goes through all of the lines 87 00:04:15,990 --> 00:04:19,290 in the is_leap function and then at some point 88 00:04:19,290 --> 00:04:23,100 it will return a value that could be True or False, 89 00:04:23,100 --> 00:04:25,110 and the True or False is going 90 00:04:25,110 --> 00:04:30,110 to replace the is_leap year part in line 15. 91 00:04:30,330 --> 00:04:31,650 And then we end up having 92 00:04:31,650 --> 00:04:33,450 an if statement that checks, 93 00:04:33,450 --> 00:04:37,770 is both sides True between the "and" , so is the first part 94 00:04:37,770 --> 00:04:39,870 of the condition True and after the "and", 95 00:04:39,870 --> 00:04:43,833 is it also true in which case we will return 29. 96 00:04:45,450 --> 00:04:46,980 Now the next step is, 97 00:04:46,980 --> 00:04:50,610 if the user's not checking for a leap year February days, 98 00:04:50,610 --> 00:04:54,120 then we can simply use that list where we've got the number 99 00:04:54,120 --> 00:04:58,710 of days in a month, month_days and we pass in the index. 100 00:04:58,710 --> 00:05:01,440 So notice how month_days is organized 101 00:05:01,440 --> 00:05:04,260 from January all the way up to December, 102 00:05:04,260 --> 00:05:06,630 so 1 to 12, 103 00:05:06,630 --> 00:05:09,178 but of course, because we're working with a list in Python, 104 00:05:09,178 --> 00:05:11,610 it starts with index 0. 105 00:05:11,610 --> 00:05:15,180 So 31 is at position 0. 106 00:05:15,180 --> 00:05:16,500 The month that's coming in 107 00:05:16,500 --> 00:05:20,010 as an input is going to start from 1 up until 12. 108 00:05:20,010 --> 00:05:23,130 So we need to subtract the input month by 1 109 00:05:23,130 --> 00:05:26,970 in order to get it on the same frequency as the index 110 00:05:26,970 --> 00:05:28,530 for the Python list. 111 00:05:28,530 --> 00:05:30,750 And then we can simply use that as the index 112 00:05:30,750 --> 00:05:34,050 inside the square brackets to access the number of days 113 00:05:34,050 --> 00:05:37,413 in that month and return it as the output. 114 00:05:38,610 --> 00:05:41,670 There are many ways that this program can fail 115 00:05:41,670 --> 00:05:44,580 and one of those ways is if a user enters 116 00:05:44,580 --> 00:05:47,250 a month that is beyond 12, 117 00:05:47,250 --> 00:05:50,790 if they put in month 43, which obviously doesn't exist 118 00:05:50,790 --> 00:05:54,510 and we've only got 12 values in our month days list. 119 00:05:54,510 --> 00:05:56,940 So you could add in checks and balances 120 00:05:56,940 --> 00:06:00,510 for these things as well, as well as many other edge cases. 121 00:06:00,510 --> 00:06:01,492 But to keep it simple, 122 00:06:01,492 --> 00:06:04,140 we've just got the main task addressed 123 00:06:04,140 --> 00:06:06,510 in our program and hopefully 124 00:06:06,510 --> 00:06:09,180 you managed to get pretty much all the way there. 125 00:06:09,180 --> 00:06:11,640 If not, feel free to go back to your code, 126 00:06:11,640 --> 00:06:14,733 edit it, and make sure that it works the way you want it to.