Python Jumpstart by Building 10 Apps Transcripts
Chapter: App 3: Birthday countdown app
Lecture: Sketching the program flow
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Over here in PyCharm, let's start working on our birthday app. So as usual, we are going to come over here
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and pick a new Python file, and call it program. Now we are going to start out by having a header, then the next thing we are going to do is
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we are going to ask the user for their birthday information, and then we are going to compute the days between now and that birthday they entered,
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and then finally we'll tell them whether their birthday is coming up how many days, that sort of thing.
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So we could just write this out in one giant series of events, but I find it much easier to think about this in small little steps,
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kind of like I just described, so we can do that with functions. So we are going to start by actually defining a function
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and the purpose of this function is to get the input from the user and return it any time that we need it. So let's say get_birthday_from_user().
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So remember, to define a function it always starts with a keyword def, and then the function name, any parameters
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if it takes none, you just have open close parenthesis and a colon. And then you indent to define the code block that is the function body.
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Notice when I hit enter, PyCharm automatically took care of that for me. Now, one thing we can do is we can just kind of sketch this out
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and if I want to define the function but not really implement it or write the details of it here, I can just say pass, right?
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So the other thing that we are going to do is we are going to compute the days between two dates so we'll say compute_days_between_dates(),
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all right, and all right pass again just so we can go on and sketch out the rest of the app. Now notice, PyCharm has put a little squiggly into here
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and there is a warning that says this is a PEP 8 violation, now PEP 8 is the standard for how code should be written in Python,
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you don't have to follow it but pretty much everybody does for the most part, and, one of the rules in PEP 8 is that
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when you have two functions that are stand alone functions, there is supposed to have two lines between them.
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PyCharm actually knows how to fix many of these and I can hit command+alt+L and it will do whatever it needs to fix it.
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Now the next thing we are going to do first we are going to get the information from the user, we are going to compute the days
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and then we are going to say def print_birthday_information(), something like that. And again I am going to pass... and there is one part
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I kind of omitted because I don't really think of it as an operation, but it is something we are going to do, is we are going to print the header,
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and let's just put pass really quick. So that is kind of the steps of our app there we are going to print out the hello,
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welcome, get the information from the user about their birthday, compute whether that is in the past or the future,
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how many days and then we are going to use that to print out the information.
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The last thing to do is actually just orchestrate this into a main method, so we'll define a main method,
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here some programming languages like C++, C# and so on, they require you to actually define a main method called main,
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there is nothing like that in Python, this is just a convention. So, over here, we are going to first start
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by printing the header and then we are going to get the birthday information from the user, we are going to store this in a variable
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but just hold on for a minute there, we are going to compute the days between the dates,
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and then finally, we are going to print the birthday information. And then we'll be done.
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Final thing is we are going to be returning some information from this, we are actually going to return a date object
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that represents the real birthday, so we'll call this b-day here, and this birthday we are going to need to pass off to this function,
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so we have the birthday, and we are also going to need to know what time it is right now and I am just going to put none
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because I don't really want to talk about that what that is just this moment, but we are going to get to that right away,
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so we are going to call get birthday from user, get their birthday, we'll compute what the time is now, we are going to compare the times between these
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and this is going to actually give us number of days, like so, and then we are going to pass this on here and we will print this out.
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So you can see that PyCharm is actually showing us that hey, you are trying to use the return value of this function,
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and over here you can see we just say pass they are not actually returning the value. So our next job is to go and implement
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each one of these functions, so this flow works as we expect.