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Welcome back and this lecture we're going to take a quick little detour to talk about how you can create

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your own error handling pages.

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That is if you have a four or four error instead of showing that default not found four or four page

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that we saw earlier in the section we can show our own four or four HTL template so to set up the handlers

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for that in the error pages directory and then link those using a blueprint.

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Let's head back to our text editor and show you how it's done.

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All right.

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Here we are back at our text editor what I want to do is run our application as it is right now and

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see what happens when we try to reach a page that isn't available to us.

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So if we take a look here at our Web site we have the full navigation bar.

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And if I go to forward slash info I see info about our company but let's go to forward slash information

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of you that we know doesn't exist.

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So if I hit enter I right now get this default for 0 for error saying not found the requests are always

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not found that our server where we're always to do this play our own template file.

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So you've definitely worked for other Web sites that show their own customized four or four page.

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We're now going to show you how you can do that with flask in order to make that happen.

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I'm going to stop serving this and come back.

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Remember we have a directory called Air underscore pages underneath that directory by convention.

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We call it handlers dot pi.

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So we're going to create a new file which is essentially a view up high file.

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But for the error handling.

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So in order to distinguish it from just typical views we're going to call it handlers dot pi.

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So again this file that I'm at right now is called handlers dot pi.

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And what this is going to do is it's actually going to serve the views of those particular error pages

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sort of say from flask import blueprints and also render template and then we'll say error underscore

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pages is equal to a blueprint.

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And then we're going to call this error pages and then passen the builtin name variable.

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Now we're going to do is say at error pages.

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So instead of saying dot route we're going to call dot app underscore error handler because this isn't

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just a basic routing since we don't know what the user is going to provide for it for or for air.

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Instead we're using the app underscore air handler to connect it to a general air and then we pass in

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the error code that we want to connect it to.

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So in this case we're going to connect to a 4 0 for air and you can google around for the various h

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T.M. codes so forfour is just one type of air which is kind of a not found error.

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And then we'll see if error underscore for 0 4 and then we pass in the error that was actually found.

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So this is the view that's going to happen when you get a page that isn't found.

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And we're going to return render a template and we're actually going to set this not underneath the

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regular templates folder.

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Instead we're going to have the error templates set apart in their own error pages directory.

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So the template is going to come from error underscore pages forward slash 4 0 4 h m l and then I'm

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going to say comma for 0 4.

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So notice what's happening here.

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I'm not just returning this render template function I'm actually returning a tuple where the first

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part of it is the rendered template and then I say comma for 0 4.

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So keep that in mind we haven't actually done something like this before because we haven't use that

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app.

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Underscore error handler before but this is the main approach for setting up your own templates to be

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served for a particular errors happen.

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So now we need to do is actually set up this error underscore pages directory within our original templates

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directory.

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So if I expand templates right now I see Base 8 team.

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In this index page to melt info.

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Tim L. I'm going to create a new folder here called error underscore pages and this will allow me to

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separate my specific error templates from my other templates.

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So now underneath error pages I'm going to create a new file called for 0 4 h T.M..

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So this is for 0 for the H Tim L and it's underneath the error pages.

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So directory of templates and what you can do is basically write out whatever you want to show up for

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the four or four page.

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What's nice about this is I can then extend from base H.T. mail that way even if a forward for error

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occurs the user still has access to the navigation bar.

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So say extends from base T.M. and then we'll set up our block called content and here I'm going to have

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a Jumbotron that basically tells the user let's say four or four page not found

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so if you ever want to add in more errors.

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All you need to do is come back to the handlers thought py file.

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So essentially the views file for errors and then you just add in whatever errors you want.

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So for example if you're interested in a 403 error so that's the kind of error that occurs when something

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is forbidden.

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So maybe you're trying to update someone else's blog posts without having permission.

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That's a 4.

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0 3 error.

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The way you would do that is pretty much exactly the same.

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You just change the code.

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You would say error underscore pages dot app underscore error handler passen that particular code.

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So if 403 is forbidden access and then we say DPF error 0 3 you pass on the actual error and then will

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we say here is return render template and then we would just set up another template for that.

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So I'll say error pages 4 or 3 that each T.M. and then we say comma and we actually pass in the integer

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code for that.

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So that basically connects us to that actual air.

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OK so since we're saying four or three H-2A l Let's go ahead and create one more template.

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We'll say new file for over 3.

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The H team L and this is actually actually going to look pretty much exactly like the Frot for.

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So going to copy and paste this except I'll say it's sort of four or four page not found.

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I will just type out for three forbidden access also access for bin and then the last thing for us to

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do before we actually test this out is make sure we actually link this blueprint to our in it that PI

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file.

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So we have this blueprint called error pages and it's underneath this handlers that pile underneath

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err pages underneath puppy company blog.

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So I'll come over to it thought pie and we're going to do a very similar thing to what we did here.

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We're going to say from puppy company blog dot and in this case it's called Air underscore pages will

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say handlers import error underscore pages and then we're just going to register that will say take

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the app and register that blueprint of error pages and save those changes.

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So now that will link those two additional views 4 4 0 3 or 4 0 for errors.

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So let's check it out.

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We're going to be will check the 404 error right now because we don't have any logging permissions set

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up.

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But as long as that works we should be able to see the idea of it.

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So I'm running my application.

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Let's go ahead and go to the home page.

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Let me bring in my browser.

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So here's my browser Papy company blog about everything looks good.

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Let's go ahead and go to a page that we know this exists.

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I was going to type in some random letters here and now I get back my custom template for 0 4 page not

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found.

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OK.

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So that's how you can perform error handling of your own custom templates.

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Just to review what we did here is recreated underneath this error pages directory a handlers that pi

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file.

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So you could call those views up high but by convention people call it handlers up high.

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We set up our blueprints connecting it and then we call error pages dots and then notice here that difference

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and set of that route we say app underscore error handler pasand the actual HTML error you're looking

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for then passen that error.

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Connect it to a template and then also remember repassing 8 were returning a tuple really for this app

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error handler to handle in the back and you'll say comma and then four or four or whatever the code

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happens to be.

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So here flask is actually performing a lot on the back end for you.

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Essentially all you need to remember is to call app underscore air handler and to return the tuple including

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the rendered template and the actual code beyond that flask is doing a lot more for you on the backend.

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Then we just create our HTL templates here of whatever you want to display for any given error.

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And then remember we wanted to link the actual blueprints.

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All right.

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That's it for handling errors.

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I hope that was useful to you.

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Coming up next we're continue on with the main part of the project we'll see at the next lecture.