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Welcome to this lecture on decorator's we're not going to discuss a more advanced Python topic which

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is known as a decorator and a decorator allows you to decorate a function.

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So this is just what that word decorate actually means in this context.

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Imagine you just created a function in Python.

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You have the simple function and it does some stuff and then return something.

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Now imagine that you wanted to add some new capabilities to the function you wanted to keep the original

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simple stuff but now you want to add more abilities by doing some more things and then returning something

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else.

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So I have two options.

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You could just add that extra code that extra functionality to your old function just like we did here.

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It took that same function and then added some more stuff to it.

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Or you could create a brand new function that contains the old code and then add the new code to that.

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But what if you then want to remove that extra functionality.

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So neither of these solutions is actually pretty good because then you'd either have to use the old

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function or delete the new code manually.

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So is there a better way.

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Maybe if we can have some sort of quick on off switch to quickly add this functionality or remove it

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at our leisure.

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So Python has decorator's that apply to tack on this extra functionality to an already existing function

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and they're going to use the at operator and are then placed on top of the original function snake actually

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easily add on extra functionality with a decorator.

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So here we have our original simple function and then we can decorate with some decorator to add in

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that extra functionality to the function.

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So this idea is actually pretty abstract in practice of Python syntax.

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So what we're going to do is we're going to go through the steps of manually building a decorator ourselves

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to show what the operator is actually doing behind the scenes.

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Again when we're actually using the operator and decorators with flask we're pretty much just going

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to tack on the operator and it's just going to be a single line.

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But to really understand what's happening behind the scenes in this lecture we're going to build out

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that decorator process completely manually.

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OK let's begin by thinking about functions within other functions.

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So remember I could have a very simple function such as a function called Hello.

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And all this function does is it just prints out Hello.

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So if I save that and I actually run it at the bottom here and I run this file I get back up one line.

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Let me expand this a little bit.

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I get back.

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Hello.

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OK.

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So now let's have hello.

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Accept a parameter such as a name.

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So by default the name will be Jose and instead of printing Hello we're just going to say the hello

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function has been run

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and then we're going to find a function inside of the hello function and it does seem strange to you.

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Go ahead and review the scope lecture from earlier.

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But I'm going to have another function here called greet.

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And in this function instead of printing something I'm going to be returning and I'll say space is here.

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This is inside

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and then what I'm going to do here is I'm going to print the result of calling greet.

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So that means when I call hello and execute that function I'm going to print out the hello function

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that's been run then I'll define discrete function and then I'll actually call and print that function.

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So let's check it out.

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Let's run hello and see what happens.

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So here I'm getting the hello function has been run and then this is inside the grid.

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So to you if you want to have this extra spacing I kind of like spacing because it's enough.

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It's a good way to visualize that great insight.

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Hello.

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And in fact let's do this one more time.

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We're going to say create a welcome function that's going to return.

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This is inside let's say this insight welcome save that and then I'll call greets and also call welcome.

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So now when I run this I get back to the function has been run.

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This is inside.

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This is inside a welcome.

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So I'm both calling Hello function defining greeting welcome functions and then executing those greet

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and welcome functions.

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Notice all of this Lines 2 through 11.

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Those are all happening within the helo function itself.

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So zoom out a little bit so we can see the whole picture.

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But again all of this codes inside this one helo function.

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Now let's talk about actually returning a function.

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This is something we haven't seen before.

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So we've briefly seen already functions within other functions that we haven't actually seen the idea

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of returning a function.

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So I'm going to do the following.

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I'll see if the name provided is equal to Jose then return grete

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else.

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Return welcome.

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OK so let's think of what's actually going to happen here.

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I have this halo function and it takes an unnamed parameter.

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It just goes ahead and prints Hey hello function has been run then it's going to find the function to

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find the welcome function and then if the name is equal to Jose it's actually going to return the Greek

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function itself.

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Notice it's not executing it.

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It's actually returning this entire function for you to then play around with.

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Otherwise if the name is not easy it's going to return the entirety of the welcome function.

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So let's see what happens.

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I'm going to set X equal to hello and then I'm going to say execute x.

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So when I run this knows what happens I get back the hello function has been run and then I'm going

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to print the result of executing X..

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You can clearly see this.

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So I get back to hello functions and run.

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And then this is inside green.

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So what's actually happening here.

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Well the name by default is Jose.

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So then we print out the hello function to run.

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So we just executed line 15 the hello functionals and run.

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Then we define the function.

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We find the welcome function and as the name was he called Jose.

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I'm going to return the function then upon returning the function I set that equal to x.

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So this line right here x is equal to Hello.

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This is basically saying x is equal to

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because I'm returning great here and because I'm not executing it that means I can later actually execute

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X and print out the result which is going to return.

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This is inside the Greek.

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So this is an idea that we're going to be able to use to actually manually build out decorator's.

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So again this idea is called returning a function.

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I am just going to literally return a function by calling another function.

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So let's try this again.

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I'm not going to set my name equal to let's say Sammy say that and let's run it.

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And now I see the halo function has been run.

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This is inside welcome.

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So why is it saying this is inside welcome.

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Because my name provided is no longer equal to Jose.

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So then this else executes and it returns the welcome function.

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Again it doesn't execute the welcome function only returns the welcome function.

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It's only when actually execute X here and print out the result that I get to see this is in sidewalk.

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So this is known as returning a function.

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Now we can also use functions as arguments.

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This is the other main idea we need to understand for creating our own decorator's.

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So so far we've reviewed functions inside functions returning functions and the final thing we need

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to talk about is functions as arguments are going to create a function called hello and this one is

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just going to return.

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Hi Jose.

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I'll create another function called other and it takes in a parameter func and it's going to print some

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other code.

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And then we'll print out phunk but knows what I'm going to do here.

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I'm actually going to execute phunk so I'm going to assume that func flips assume that the func passed

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in is a function.

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So again I'm taking this as a parameter instead of my function and then I'm actually going to execute

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it.

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So let's say that and see what happens when I say other passen.

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Hello I'm going to run this again and I see.

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Hi Jose and some other code.

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So what's actually happening here is I've defined this function.

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Hello which returns.

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Hi Jose.

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And then I'm passing in that function notice here I'm not calling it I'm just passing it in and then

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this other function is going to take it in.

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It's going to print some other code and it's going to grab the function that was passed in this case.

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Hello.

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Execute it to return.

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Hi Jose.

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And then print out that result.

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Which is why when I run this I see some other code.

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Line 5 and then.

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Hi Jose.

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Which is the product of line 7 which is passing in the hello function executing it and returning Hi

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Jose to be printed out.

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So this is known as passing in a function as an argument.

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Now that we understand these three fundamental ideas of functions within functions returning functions

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and using function as arguments we can now actually build and create our own decorator.

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So let's try this out.

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I'm going to create a function called new underscore decorator and it takes an some phunk than inside

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of it.

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I'm going to create what I would call wrap func a wrapping function and it's going to print some code

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before executing phunk then I'm actually going to execute phunk.

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So remember this is the phunk that's passed in here.

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So that has to do with the global scope I'm going to be able to call it and then I'm going to print

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code here after executing phunk And then when I'm going to do is my new decorator function is going

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to return rap funk Sozzi and try to understand the idea of what's happening here.

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This function new decorator accepts a function then inside of the new decorator function I create a

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wrap function that can add some code before I call func execute func and then add some more code such

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as printing code here after executing func and then this new function which has effectively decorated.

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Or add more functionality to phunk is then going to be returned.

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And then finally I'm going to create a function that needs this declaration.

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So I'll say this func needs a decorator going to say just prints please decorate me.

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OK so let's see what happens when I say just call phunk needs a decorator by itself.

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So if I run this code and I get myself a little more room here it says please decorate me and that's

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it.

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Which makes sense because that's all it's being printed here.

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It says Please decorate me.

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I call Falconis decorator and that's it.

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Now let's try the following.

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I'm going to say phunk needs a decorator and I'm going to assign it to new decorator passing in phunk

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it needs decorator so what does this is doing is I'm taking what phunk needs a decorator currently is

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which is just printing out please decorate me.

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I'm taking this entire function right here and I'm passing into new decorator the new decorator is going

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to take the funk needs decorator and it's going to build it into wrap function.

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It's going to print some code before executing it then it's going to execute it and then it's going

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to print some code after it and it's going to return that new repped function and I'm re-assigning that

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to function means decorator.

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So now let's see what happens when I actually execute phunk needs decorator.

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I run this and if I expand this I can see the results and I'll get back some code before executing the

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function.

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Please decorate me and code here after executing phunk.

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So this is basically what a decorator does all the decorator does is it takes in the function that you

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want to decorate.

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It creates a new function out of it with some extra functionality either before or after it or both

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and then execute the function as well.

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And this new wrapped version of your function gets returned.

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Now instead of doing this sort of re-assignment which can be a little ugly and said well we can do is

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we can use the app notation to say new decorator and that performs the exact same thing that we just

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saw earlier.

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So that line performs essentially what line 16 is showing here.

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So Line 12 just tagging this function with that new decorator is the same as doing this right here.

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Except this is really easy to turn off anon.

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We can just commented out if we don't want it to be decorated or commented in.

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If we do want it to be decorated.

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Now we no longer need to add in this code manually or copy and paste this entire function and have kind

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of two versions of it instead.

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I can have this decorator function which I can easily then turn off or back on.

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OK.

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So let's see now that decorator in action I'm going to save this.

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Run this file again.

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And if we expand this to see the results I get back some code before in the function please decorate

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me code here.

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After executing function again let me just walk through everything here because this is basically it's

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all decorator is we have a function that needs decoration.

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And what we do is we decorate it with this at symbol new decorator and then that's going to be passed

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in to this new decorator function which is then going to construct inside of this entire new decorator

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function.

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It constructs this new wrapping function.

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You can execute some code.

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Call the function then execute some more code after it and you return this new like souped up or decorated

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version of your original function.

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And then if you ever want to actually wrap or decorate your function you just tag your original function

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with this symbol.

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And then the name of this decorator and that's it.

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OK I know this can be pretty complicated.

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And luckily we're never actually going to build manually our own decorators.

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Instead we'll be using the built in decorators that flask provides for us and we'll just be tagging

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them at and then decorator.

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So if you didn't understand this fully and wouldn't feel comfortable building out your own decorator's

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I would pretty much say don't really worry about it because you'll never have to actually do this when

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working with flask yourself instead you'll just be doing what we have here on line 12 adding a simple

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decorator line of code.

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But I do want to show you what's going on behind the scenes in case you are interested in it.

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All right that's it.

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We'll see you at the next lecture.