Python Jumpstart by Building 10 Apps Transcripts
Chapter: App 3: Birthday countdown app
Lecture: Dates and times - getting the birthday

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0:00 Now we have the basic structure
0:02 the basic shape and building blocks of our application
0:05 let's fill them out. Let's start at the beginning which is a super easy
0:08 we are just going to put our standard print statements.
0:13 There you go, nothing new there.
0:16 Now the next thing is get the birthday from the user.
0:19 And what we need to return from this method
0:22 is an actual datetime,
0:24 not just some text or something like that
0:26 but we'll start by receiving text
0:28 we'll ask the user a question
0:29 we'll get some text and then we'll turn that into a date
0:31 there is actually a bunch of ways to do that
0:33 we'll do the most straightforward way for now.
0:40 So we are going to ask the user when were they born
0:42 and then we are going to use our input
0:44 to get the year, the month and the day.
0:48 So we'll say year, like this, and we'll give it a little...
0:53 now the next thing I want to do
0:54 is kind of the same thing but for the month
0:56 and I could copy and paste this, I could retype it,
0:58 or in PyCharm I hit command+D
1:00 and it will just duplicate whatever you have selected,
1:02 that is super handy,
1:04 then I'll say month, I'll change this to be appropriate here,
1:07 I'll say month and mm, and same thing for the day.
1:17 So I call this year, month and day,
1:19 and it turns out we are not quite done
1:21 with the section but let's just see what goes wrong
1:22 and then we'll come back and fix it.
1:24 So the next thing I need to do is work with dates,
1:27 and dates are contained in module called datetime,
1:29 and we actually like before with our random
1:34 we have to import datetime,
1:35 so we can come over and say import datetime,
1:39 and then we can come down here
1:41 and now we can work with it,
1:42 we'll say let's call some birthday,
1:46 and we are going to come here and we'll say datetime,
1:49 that's just the module we've imported,
1:50 now the next thing is just a little confusing when you first see it,
1:53 there is datetime.datetime,
1:56 ok, so what is going on here?
1:58 This is the module that we imported,
2:00 and within there, there is several things that represent dates and times
2:04 there is datetime, which represents
2:06 a day on the calendar and a specific time on that day,
2:10 there is day, which is just a day in the calendar
2:13 without the time component,
2:14 there is time, it's just a time part
2:16 and there is time delta which is the difference between two datetimes.
2:21 So, maybe it's a little unfortunate, maybe not,
2:24 but we say datetime.datetime and this is a class
2:28 so we can allocate a new instance of it.
2:31 So we have the year, the month,
2:33 the day, the hour, minute, second,
2:35 we can omit everything but the year if we'd like,
2:37 so we are going to put in a year, month, day,
2:41 and the last thing to do is we need to get our birthday
2:44 that we are creating here,
2:45 we need to return this out of this function,
2:47 we need to give it back,
2:48 so that we can capture in this variable down here,
2:50 pass it along and that is super straightforward,
2:52 we just say return birthday,
2:55 and that is going to return it form the function,
2:56 you can see the little warning about not returning the value down here,
2:58 it's gone, so everything looks good,
3:01 it's not good but it looks good,
3:03 there is actually two things that are not going to work great,
3:06 let me just show a quick reformat
3:07 so we only see errors not just pep 8 warnings.
3:11 So when I try to run this it's going to be underwhelming,
3:14 notice there is no run configuration,
3:16 so I'll go over here and I'll say right click and then run,
3:18 now when it runs, you probably thought
3:21 that it was going to ask us questions like hey,
3:24 what year, what month were you born and so on.
3:27 But, remember, I told you there is no convention
3:30 around executing like a main method or anything like that,
3:33 and this is just for me to organize my thoughts, right
3:37 to sort of group this into smaller building blocks
3:40 one way we can trigger this to work
3:42 is we can just call the main method at the end of the script.
3:44 That's not technically the best way of doing it,
3:47 but let's just do this now and we'll come back
3:50 and we'll improve upon it.
3:52 So now if I run it, you can see it says
3:54 tell us when you were born. Let's say 1974.
3:58 And it asks for the month. Ok, April.
4:02 And the day was let's say 1st.
4:04 If I enter, you can tell it's obviously not happy.
4:09 Why is it not happy, well it's a type error and it says
4:11 an integer is required but we've got a string.
4:14 Where is that? So it turns out that
4:16 these have to be numbers,
4:18 and they are not numbers,
4:19 they are things that have come back
4:21 from input which are always strings
4:23 so we need to convert them... right?
4:25 So that is the one thing that was missing here,
4:27 and we can do this in several steps
4:29 or we can just sort of combine it like this,
4:33 say int, recall that we convert from a string to an integer
4:37 by just passing the string to the initializer of the int class,
4:43 so now, these should be integers,
4:45 but if you put in something that is not an integer, it's going to crash.
4:48 And the real app we should check for this,
4:50 when we get to there handling section of the course,
4:53 we'll talk a lot about this,
4:54 right now let's assume that they are giving us valid numbers.
4:57 So now if we run it,
4:58 we should get it to work much better.
5:02 Now it is still not going to work,
5:03 in the end I think it may crash,
5:06 it may make it to the end, let's see.
5:08 Yeah. So we made it farther,
5:12 just down here we haven't quite finished this,
5:15 so we made it down this far,
5:17 let me turn on line numbers really quick for you,
5:20 so I come over here and search into settings,
5:23 under general here you can see
5:25 I can just turn on show line numbers, all right,
5:28 so now I can tell you,
5:29 when we make it down the line 31,
5:30 everything is working fine
5:31 and these are the parts not so much yet,
5:34 so let's just comment those out really quick,
5:36 I like to just maybe do a print statement,
5:38 as I go along, just to kind of see as it builds up,
5:42 right, if it's a simple app,
5:44 so let's go over here and just put in some numbers,
5:48 and you can see we've actually generated
5:50 a datetime object and we've returned it here
5:53 and it's... ok, so it looks like this step is totally working.