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- [Instructor] Hi and welcome back.

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In this video, we're going
to be fixing the error

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that we found in the last video.

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In order to do that, we're going to need

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to be able to see what caused the error.

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So what to do is to download
the Heroku Command Line

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which gives us access to
a bunch of Heroku things,

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including the output of our
application in the console.

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That output, we can hope,
will have some information

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to help us troubleshoot this error.

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Also, if you can't
troubleshoot a specific error,

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it will also help me help you

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if you put the Heroku
logs out in the course Q&A

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if you have any problems.

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So to download the Heroku Command Line,

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just go to this URL,

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devcenter.heroku.com/articles/heroku-command-line.

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And then it's very simple for OS X.

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Just download and run the OS X installer,

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and for Windows, the Windows installer.

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Once you've done that, it's really simple,

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just go to your terminal.

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Make sure to quit your terminal,

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entirely exit the terminal,

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and then restart it again,

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so to reload all the changes
that Heroku has made.

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And then we're gonna do heroku login.

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And this is going to prompt you

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for your Heroku email
and your Heroku password,

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so type those in and then
you will be logged in

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to the Heroku Command Line interface.

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After that, once you've done that,

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do heroku logs --app

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and then we're going to
put in the name of our app

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which is stores-rest-api,
if I'm not mistaken.

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And here we have the
logs of our application.

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So as you can see, this stuff here

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was the starting up of the application.

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It says things, like, uWSGI is running

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in multiple interpreter mode,

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spawned master process,

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and then at the end,
it says, state changed

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from starting to up.

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That means that the
application's now running.

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Then we did our request

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for the path, a forward slash,

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we just access the home of the application

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and I told you that
this wasn't gonna work.

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This is not meant to be a
browser, blah, blah, blah.

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But really, the error
was something different

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as it seems from the logs.

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Apart from the fact that this path here

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doesn't return anything,

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that should have returned
an error code 404,

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which is Not Found,

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but really, what we saw
coming back is an error 500.

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500 means internal server error

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and it means that the
server couldn't tell us

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what was wrong, but something went wrong.

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So what we've got after that
is exactly what went wrong.

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Normally in these tracebacks,

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it starts at the point where
the error was returned to us,

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so it starts at the request dispatcher

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and then it starts at
try_trigger_before_first_request,

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and finally at the end here,

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it is our code, something
that looks familiar,

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db.create_all.

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And if you remember, we've
got this in our app.py

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and what that does is that
it goes to the SQLAlchemy

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and creates all of the tables,

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but there was an error, NameError,

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the name db is not defined.

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So that's interesting

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because, well, why is it not defined?

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We know that it's not
defined, so let's go into Atom

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and load up our app.py

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and see if we can identify
why it may not be defined.

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This is a really common error.

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Well, we've got all our imports up here.

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And then down here,

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we've got our
before_first_request decorator,

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which is the create_tables method,

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which is what runs db.create_all.

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But here's the thing,
where is db imported?

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'Cause it's certainly not here.

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And as you can see, db
is imported down here

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but db is imported
inside this if statement.

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Do you remember what
this if statement means

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or when this code is executed?

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I hope you did.

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This here runs when we
directly execute app.py

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from using the Python commands.

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If we do python app.py

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__name__ of the file,

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you use main.

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And therefore, this runs here.

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We import the db and then we run the app.

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However, when we run
the app through uWSGI,

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uWSGI is loading the app variable

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and running it itself.

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It is not running the app.py file.

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So therefore, this never runs.

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app.run doesn't run either

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but uWSGI runs the app for us.

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But the problem is that we're
not importing db anymore,

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so when it comes to
running this method here,

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it doesn't know that db exists.

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So how do we fix this problem?

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You may be tempted to
put this thing up here,

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but let me tell you, if you do
that, bad things will happen

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because of something
called circular imports.

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So if we put that up there,
we'll get a big mess.

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So what we have to do is create a new file

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which I'm gonna call run.py,

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although really it's
not gonna run anything,

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but nevertheless, run.py.

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And what run.py is gonna do
is it's going to import app

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and it's going to import db.

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Now, at the end, all that we have to do

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is say db.init_app(app).

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So essentially, it's doing
exactly the same thing

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that we're doing down here

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but it is not importing
the resources themselves.

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So hopefully that makes sense.

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And now, this run.py file

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also needs to contain the decorator,

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I'm gonna cut that and put it in here,

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so that when we run this file,

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this decorator does get created

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and it has access to
the db variable as well.

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So I'm gonna save both of these files

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and there we are.

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Now, we also have to make sure

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to change the uWSGI reference.

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We no longer want to
load up the app's app.

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Now we want to run run.py app,

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which is the same app,

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but if we load up the run.py decorator,

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that's going to execute this code here

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but it's gonna have
access to the db variable

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which it didn't in app.py.

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So just make sure in your uwsgi.ini

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to change the module to be run:app.

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And after that, let's
go back to our terminal

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and we're gonna clear this

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and we're gonna do git status

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and run.py and commit everything.

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In order to commit everything,
we can do git commit -a.

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So we're gonna do -am to
also type in a message

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and we're gonna say,
"Fixed not importing db

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"when running the app."

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And then we're gonna push.

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Once that's pushed,
we're gonna go to Chrome,

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which is where we've got our API

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and to make sure to go
ahead and press Deploy.

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So I've already deployed,
so I'm gonna deploy again,

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and that is it deploying.

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Now once that's deployed,
we're gonna go ahead

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and see if the output is any different.

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Notice that when we access the root,

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the homepage of our app,

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we should expect a 404 Not Found

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as opposed to a 500 Internal Server Error.

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404 Not Found is going to mean

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that there was no endpoints
defined for that address.

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500 Internal Server error means
that something went wrong.

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So let's go ahead and view this.

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And there we go.

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So now we get a 404 Not Found.

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That means there wasn't an error.

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It's just that we didn't define a path

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for the forward slash by itself.

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So what to do now is go over to Postman,

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change the URL to this URL here

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and try that everything works.

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So let's do that in the very next video

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and I'll see you there.