Program Flow

Quick reference

• 00:04 We talked about functions in the last couple of videos.
• 00:06 I want to continue on and talk about something else that deals with functions,
• 00:10 specifically program flow.
• 00:12 I'm just going to create really quick
• 00:17 our namer Function one more time and
• 00:22 let's return Hello as name.
• 00:27 Okay, so if we print out namer John, save this and
• 00:32 run just to make sure it worked.
• 00:35 We get Hello John, so far, so good.
• 00:39 I mentioned earlier that functions don't get run unless you specifically call them,
• 00:44 and you call them by just writing out their name,
• 00:47 and then passing in the parameter.
• 00:48 Python starts at the beginning of every file, and
• 00:52 it starts on line one and reads down, and it goes line by line.
• 00:56 So first, it imports this module, then it clears the screen.
• 00:59 And then it sees this comment, doesn't do anything, it ignores this line.
• 01:03 And then it sees this function and it reads it into memory, but
• 01:06 it doesn't do anything.
• 01:07 We already understand this.
• 01:09 So I want to ask, if we were to copy this and
• 01:12 delete it and put it up here, what do you think would happen?
• 01:15 Well, let's find out.
• 01:16 If we save this and run it, no, we get an error.
• 01:19 What's happening is Python starting at the top like I said, does this line,
• 01:24 this line, and this line, this line comes to here, it says, okay, call namer.
• 01:28 And then Python goes, whoa, whoa, wait a second, what is namer?
• 01:32 It has no idea, because it's still on line five,
• 01:34 it hasn't gone down the line seven yet, and learned what namer is.
• 01:38 It hasn't read this into memory yet, and so we get an error.
• 01:43 So it's very very important with functions, and it's sort of the convention
• 01:47 to put all your functions at the very top of your program.
• 01:51 If you have 100 functions, put them all at the very top.
• 01:53 If you have five functions, put them all at the very top.
• 01:56 That makes sure that you don't accidentally call a function before
• 01:59 it's been read into memory.
• 02:01 So that's the program flow, so you've gotta be sure and keep an eye on that.
• 02:05 And it's not just because of this.
• 02:07 I mean, okay,
• 02:08 this is one simple function and here we know we're going to call it right here.
• 02:12 We can sort of be on the lookout and
• 02:14 make sure we put this call beneath this function.
• 02:19 But it's not always that simple because inside of a function,
• 02:21 you can call another function.
• 02:23 You can kind of lose track of where all your functions are.
• 02:25 So that's why it's a good idea just to keep them all at the top of your file.
• 02:29 So I recommend you do that.
• 02:30 So let's create a function, another function, let's call it color.
• 02:34 No parameters, and we just want to print out.
• 02:37 I like BLUE capitalized, Don't forget your colon, right?
• 02:42 So let's change this around, let's this make this really easy.
• 02:45 Let's just print this and let's just call color.
• 02:49 And if we save this and run it.
• 02:53 And then since we changed this to not need a return, we can just call our namer.
• 02:58 Let's run this guy, so we get hello John in blue.
• 03:02 Everything works fine but now if we take our function call, and
• 03:07 for instance, we stick it here right after namer.
• 03:10 In this case, namer is the function we're calling or passing in our parameters so
• 03:15 this should work, right?
• 03:16 Because this function is read into memory before we called it.
• 03:21 If we run it, we're going to get an error because inside of this function,
• 03:25 we're calling another function and that function is down here.
• 03:28 And again, Python hasn't read that in the memory.
• 03:31 The program flow hasn't reached that far yet.
• 03:33 So it starts at the beginning.
• 03:35 Does line one, line two, reads this into memory, doesn't really know what color is,
• 03:39 but that's okay, because we haven't called it yet.
• 03:42 But then right here, we call a namer and executes this and
• 03:46 then it tries to execute this, and it says, what is color?
• 03:49 I have no idea because the program itself hasn't gone pass line nine yet.
• 03:53 Just another reason why you want to keep all of your functions
• 03:58 at the top of your program before you call any of them.
• 04:02 It's just sort of best practices to do that.
• 04:04 That's program flow.
• 04:05 Very interesting and important thing to understand just a concept you need to
• 04:08 understand pretty simple just keep all your functions at the top of the file and
• 04:11 you're good to go.
• 04:12 So in the next video, we're going to look at random numbers.

Lesson notes are only available for subscribers.