2.5 Python Functions - IP
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Video Transcription
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>> Hello, everyone and welcome to intro to
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Python here on Cybrary On-demand.
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I, as always, I'm your instructor
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Joe Perry and I as always,
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I'm very excited to have you here.
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This is one of the Python lessons that I
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really love to teach because
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functions are the fundamental component
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of really every programming language.
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A lot of the things that we've touched on in
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previous videos are going to make more sense
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now and you're going to be able to do
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just so much more with
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Python after this video and after this lesson,
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now that you will actually understand what functions are,
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how they [NOISE] work, how they're used and
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all the incredible things you can do with them.
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The objectives of this lesson,
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we have three of them.
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We're going to learn to write Python function.
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Instead of working in our shell,
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we've actually been spent a lot of time
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working on an actual Python file.
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To do that, we're going to learn
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about input variables which
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are called arguments and we're going to learn
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about the output from functions,
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which is called the return.
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We've got our terminal open, we've got our
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VM open, we're going to do vim.
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We're going to make sure we're on the right lesson here.
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The right lesson folder,
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because I don't think we are, we are not.
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CD, this is not important to those
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of you working at home unless you've
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reconstructed my file structure.
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But I like to be in the right lesson folder,
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it just makes me feel a little bit better.
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Less than five PWD, right place, cool.
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We're going to do vim, and we're going to do funcs.py.
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First thing as always,
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we're going to add our shebang line/user/bin/python3.
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Now, I mentioned that
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there are inputs and there are outputs to functions.
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The way we create a function in Python,
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the first thing we're going to do is we're going to use
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what is called the def keyword.
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What deaf says it's
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a shorthand of the Python interpreter that says hey,
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then the rest of this line is defining a functions.
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Def means defined.
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Def func_1.
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Function is a keyword in Python that
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can get a little bit weird if you use it too much.
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We'll call this func_1. Then we're going to give
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it just a pair of parentheses with no other information.
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Then we're going to have this return line.
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I'm going to break this out piece by piece.
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[NOISE] Def, function definition,
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keyword, func_1, function name.
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Again, just like with any other variable name,
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this function name can be whatever you want to call it.
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You can call it foo, bar,
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baz, whatever you want it to be named.
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That's just the name of your function.
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Parenthesis, they are
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the indicator that there is a function and
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the values inside of them are called the arguments.
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Here we'll actually go ahead and put in
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a couple of arguments so that you can
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see what those look like.
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A and B.
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These variables are just like any other Python variable.
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They are Tupperware for your brain.
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They're just an abstract data storage location.
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What's really useful about
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function arguments is that they are used to tell
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your function what logic you're going to be
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performing and what you're going to be
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performing that logic against.
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Here now that I've identified that those are arguments,
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we can see that for example,
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we might want to say c equals a plus b.
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Now this function, what it's actually going
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to be able to do is
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get these arguments from
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whoever is calling this function,
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whoever is actually using this function.
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It'll take those arguments,
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it will perform logic against them,
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and it will give you information based upon them.
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You've got c equals a plus b,
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but the problem is that we can't use that
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right now because of
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the fact that it's still in that function,
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we are not printing or we're not doing anything with it.
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We need to use our return argument.
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Now, return by itself is
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a keyword that you can use just to say,
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this function is done executing.
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It is the indicator [NOISE] of end of function.
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But additionally, you can give
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return an argument essentially on that line,
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even though it's not in
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parentheses like a function would be.
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But you give it a statement on that line, for example,
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return c. In this case,
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returns c means provide the value of c to the color.
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The color is what we referred to whatever line of
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code actually executes this function.
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The way you're going to call a function
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is just by addressing the way we've done with
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print and with a couple of
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other functions and a bunch of other videos.
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You're just going to say the function's name,
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func_1 with parentheses and the arguments.
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In this case we're going to say func_1
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with the arguments of 1 and 2.
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Because we're in our script,
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we're going to go ahead and use print
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here to print the result.
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Now it's worth noting,
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what you can see here is that printing is
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now a function that's got a function inside of it.
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The way this is going to happen is it's going to execute
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this internal function and the it's going to call
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print with the return value.
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You could also see this as ret_val
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equals func_1, print, ret_val.
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Here I'm going to tie
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this down a little bit so you can see it.
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That's how you assign the value of
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a function's return to another variable.
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You just give that variable and you'd put
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an equal sign and then you call the function.
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Here we have print, ret_val,
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and then we're just going to close this script and
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we're going to execute it and see what it does.
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There you can see it prints the number 3.
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We can go back and we can look and
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logically understand how that's happening.
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We give it the arguments of one and two.
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The internal logic of the function is,
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sorry, my Vim is jumping around,
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c equals a plus b,
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return c. We store that return in our ret_val,
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and we print the ret_val.
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Now it's important to note that in Python,
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if you have this function,
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but you never actually call it,
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[NOISE] nothing is going to happen.
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Because of the fact that your Python interpreter is
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going to open this script and say,
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yeah, I see a function defined,
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but I never said that function called or used anywhere.
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Nothing is going to be executed.
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In Python and in most programming languages there
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is a standard,
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a commonly used function called main.
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What main is, generally speaking,
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is going to be the actual
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primary logical flow control for your program.
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With main, [NOISE] you might call
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your other functions with some number of arguments.
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You might repeatedly call them,
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you might do something with them.
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But generally speaking, main is going to be what
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controls the flow of your program.
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At the very bottom of your program,
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we're just going to write main and actually code it.
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Now, the reason why you use functions is actually
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really well illustrated by these two lines of code here.
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Now, I'll comment these out real fast and show you.
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I could have done print 1 plus 3,
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print 2 plus 4.
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I would generally get the same result as
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printing these two return variables.
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But that only works because of the fact that we're doing
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a very simple piece of work here.
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If we were, for example,
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trying to do c equals a plus b,
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d equals a minus b,
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and e equals c to the power of
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d. Those three lines of code,
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we don't really want to write every
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single time we're trying to put them.
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We don't want to have to rewrite it.
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That's the actual true use and power of functions,
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is that they create reusable,
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discrete chunks of code that
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will do all of the work for us.
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You only have to write your code
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once if you put it in a function,
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instead of having to continually rewrite it over
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and over again just to perform some operation.
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We have our return values,
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we have our arguments, and we
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have our actual functional code.
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We now understand the concept
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of writing logic inside of a function,
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using the arguments and then
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returning the result of that logic.
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In your lab, which is going to be
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your next opportunity to really work with this,
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we're going to be going over Lessons 1
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through 5 of Module 2.
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These variables are going to learn to implement loops,
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if statements and functions in Python.
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Again, if you're an inside or pro,
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you're going to get to do that in our next tech lab,
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which is going to be right next to me.
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Well, I guess I can't point
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now because I'm not onscreen,
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but it'll be in our supplemental materials.
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If you're not an insider Pro
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in that supplemental materials,
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you will see the lab assignment,
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and you will see my solution code.
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Even if you're not an insider Pro,
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you can still perform the assignment.
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But I do highly recommend if you can then
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use the next tech lab that I created for this course.
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It's just absolutely spectacular and it can be very,
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very useful for performing this code.
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Once you come back from doing that,
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we're going to start in on the second half of
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this module in which we're going to be performing
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deep dives of all the Python datatypes that we
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very briefly addressed in Module 1.
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You're going to learn all about them.
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Next lesson is specifically going to be
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about using strings in Python.
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I'm very excited to teach you as always,
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I have been your instructor, Joe Perry.
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Thank you for watching intro to Python
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here on Cybrary On-demand.
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