Python Jumpstart by Building 10 Apps Transcripts
Chapter: App 3: Birthday countdown app
Lecture: Sketching the program flow

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0:00 Over here in PyCharm,
0:01 let's start working on our birthday app.
0:03 So as usual, we are going to come over here
0:05 and pick a new Python file, and call it program.
0:09 Now we are going to start out by having a header,
0:12 then the next thing we are going to do is
0:13 we are going to ask the user for their birthday information,
0:17 and then we are going to compute the days
0:20 between now and that birthday they entered,
0:22 and then finally we'll tell them whether their birthday is coming up
0:26 how many days, that sort of thing.
0:28 So we could just write this out in one giant series of events,
0:31 but I find it much easier to think about this in small little steps,
0:36 kind of like I just described,
0:38 so we can do that with functions.
0:40 So we are going to start by actually defining a function
0:43 and the purpose of this function is to get the input from the user
0:47 and return it any time that we need it.
0:49 So let's say get_birthday_from_user().
0:54 So remember, to define a function
0:55 it always starts with a keyword def,
0:57 and then the function name, any parameters
1:00 if it takes none, you just have open close parenthesis and a colon.
1:03 And then you indent to define the code block that is the function body.
1:07 Notice when I hit enter,
1:08 PyCharm automatically took care of that for me.
1:10 Now, one thing we can do is we can just kind of sketch this out
1:13 and if I want to define the function
1:15 but not really implement it or write the details of it here,
1:18 I can just say pass, right?
1:20 So the other thing that we are going to do
1:22 is we are going to compute the days between two dates
1:26 so we'll say compute_days_between_dates(),
1:30 all right, and all right pass again
1:33 just so we can go on and sketch out the rest of the app.
1:35 Now notice, PyCharm has put a little squiggly into here
1:38 and there is a warning that says this is a pep 8 violation,
1:42 now pep 8 is the standard for how code should be written in Python,
1:47 you don't have to follow it
1:48 but pretty much everybody does for the most part,
1:52 and, one of the rules in pep 8 is that
1:54 when you have two functions that are stand alone functions,
1:58 there is supposed to have two lines between them.
2:00 PyCharm actually knows how to fix many of these
2:02 and I can hit command+alt+L
2:04 and it will do whatever it needs to fix it.
2:07 Now the next thing we are going to do
2:08 first we are going to get the information from the user,
2:11 we are going to compute the days
2:13 and then we are going to say def print_birthday_information(),
2:15 something like that.
2:17 And again I am going to pass... and there is one part
2:20 I kind of omitted because I don't really think of it as an operation,
2:22 but it is something we are going to do,
2:25 is we are going to print the header,
2:28 and let's just put pass really quick.
2:29 So that is kind of the steps of our app
2:32 there we are going to print out the hello,
2:33 welcome, get the information from the user about their birthday,
2:37 compute whether that is in the past or the future,
2:39 how many days and then we are going to use that
2:41 to print out the information.
2:43 The last thing to do is actually just orchestrate this into a main method,
2:47 so we'll define a main method,
2:49 here some programming languages like C++, C# and so on,
2:54 they require you to actually define a main method called main,
2:58 there is nothing like that in Python,
2:59 this is just a convention.
3:01 So, over here, we are going to first start
3:03 by printing the header and then we are going to get
3:08 the birthday information from the user,
3:10 we are going to store this in a variable
3:11 but just hold on for a minute there,
3:13 we are going to compute the days between the dates,
3:16 and then finally, we are going to print the birthday information.
3:20 And then we'll be done.
3:22 Final thing is we are going to be returning some information from this,
3:25 we are actually going to return a date object
3:27 that represents the real birthday,
3:29 so we'll call this b-day here,
3:32 and this birthday we are going to need
3:33 to pass off to this function,
3:35 so we have the birthday, and we are also
3:39 going to need to know what time it is right now
3:42 and I am just going to put none
3:44 because I don't really want to talk about that
3:45 what that is just this moment,
3:48 but we are going to get to that right away,
3:50 so we are going to call get birthday from user,
3:52 get their birthday, we'll compute what the time is now,
3:55 we are going to compare the times between these
3:57 and this is going to actually give us number of days, like so,
4:03 and then we are going to pass this on here
4:06 and we will print this out.
4:07 So you can see that PyCharm is actually showing us that hey,
4:10 you are trying to use the return value of this function,
4:14 and over here you can see we just say
4:16 pass they are not actually returning the value.
4:18 So our next job is to go and implement
4:20 each one of these functions,
4:22 so this flow works as we expect.