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Welcome back in this lecture we're going to talk about the debug mode option as we learn about flask.

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We're definitely going to make some mistakes along the way.

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We can set debug equal to true in our application to help us catch these errors.

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Debug Mode also gives us access to a console in the browser.

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Let's explore all of the debug options we have by jumping over to our text editor OK here and back in

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my text editor.

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Right now we just have three views.

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There's the home page you for index.

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There's this information view and then there's dynamic routeing view where we can take in a puppy name

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and display right now in uppercase the puppy's name.

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What I'm going to do right now is change this view for puppy and I'm going to have it return sort of

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saying uppercase I'm going to have it returned the one hundredth letter of the name.

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Keep in mind not every name is going to have 100 letters in it.

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In fact most names won't.

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And then here we're going to say Index 100.

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So what's happening here is I'm basically asking for the index at one hundred and then I'm going to

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try to return it.

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So right now I'm just going to say APTA run here on line 19.

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Let me save my changes.

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Now let's run the file.

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And let's go to the home page in our browser.

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Here we go.

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So I'm at the home page in the browser and if I do something like forward slash information it says

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Puppies are cute.

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Now let's try to visit puppy and I say puppy slash Rufus Now remember Rufus doesn't actually have 100

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letters in it which means when I try to do this indexing of name 100 that's going to be an error inside

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of this function.

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So what Flast does by default is it says you have an internal server error the server encountered internal

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error and was unable to complete your request which makes sense that function inside of a web application

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has an internal error.

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So instead of just breaking down the entire site it just reports back you have an internal server error.

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That's not very helpful however.

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We're trying to debug our code.

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So instead what we can do is debug equal to true inside of our text editor.

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So let's go back and do that and come back here.

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I will set debug equal to true and then that save Let me restart my server and we're going to come back

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here.

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Let's check the home page again.

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So home page looks good.

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It says Hello puppy and what I'm going to say is could be.

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And the Rufous again and now notice what happens if I'm going to expand this.

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I get an index error.

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Now I have a lot more information about what's happening within my application.

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It says street index out of range.

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So now we're already thinking the idea hey maybe I have an index problem with my actual function which

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is exactly what was happening.

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We pass that rufous Rufus's I have 100 letters so the index is an issue and it'll give you a full traceback

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here and you notice as you go around it's say something like at the very bottom just what triggered

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the index string index out of range 100 flooder format name.

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Now what's really cool is as you hover over these particular errors with the traceback you'll get little

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console icon.

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And if you hit this you can open an interactive python shell inside of this very frame.

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Now in order to do that.

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Going to need to expand this as you scroll up here you should eventually see the full traceback error

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in this command line.

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And then if you also come back here you should see a debugger pin you're going to need that in order

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to actually access the console.

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So notice right when you set run Osei debug mode is equal to on will say debuggers active and it has

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a debugger pin.

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I'm going to highlight this debugger pin right click and then select Copy make sure don't do Control-C

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that's going to quit your server if you do that.

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But once I have that debugger pin let me go back to my browser here and back on my browser going to

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expand this again.

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I'm going to select the console and then it's going to ask me hey what was that pen.

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I'm going to paste that in.

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Click.

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Confirm pin.

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And then once you confirm it you'll be able to scroll back down here and now it says consolers ready.

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So what is this useful for.

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Well it's really nice here is I can then pass in whatever variables I want and essentially a debugger

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counsel right where the traceback happen.

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So if I type in name Ill say hey the string that was passed then was rufous and then if I type in name

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of 100 ill say another traceback here.

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Hey you have an error index string is out of range.

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So here I can explore the various variables that are actually happening inside of this view function

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and these are the two main aspects of debug.

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The first one is this fool that traceback that it's going to issue you and a lot of times just from

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this itself you'll be able to debug that if you need to play around whatever variables that are inside

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the view function or really any other page that's going on you're able to open a python console within

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a step of this traceback.

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So those are the two main things to note here.

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Remember you'll need the debugger pin in order to actually access this console which is a nice little

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security feature that's built into flask.

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One last thing.

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Keep in mind is that you should never have debug equals true when you're deploying this to production.

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Otherwise other people are going to see this debug page and be able to see your full traceback instead

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of just getting that internal server error.

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All right.

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That's it for the debug mode.

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From now on we'll be sending debug eagle to true for most of our projects to help us debug any issues

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that may come along the way.

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And I would definitely suggest to you as well as you're playing around a flask the debug equals the

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true and only set it to False.

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Once you're ready for production do you have any questions feel free to post the Q&A forums.

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We'll see you in the next lecture.