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It's always good to start small, so let's create a simple Flask app with a single view and route.
New Terms
View: A view is a function that returns an HTTP response. This response has to be a string but can be any string you want.
Route: A route is the URL path to a view. They always start with a forward slash / and can end with one if you want.
dunder: A quick way of saying "double underscore".
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We call our Flask script an app.
0:00
The app is where all of the requests come
to.
0:03
The app then sends those requests to the
correct function or view.
0:05
It finds this function through the route.
0:09
And, you know what, that's way too many
words.
0:10
Bring on the graphics.
0:13
[SOUND] Okay, so the app gets all of the
requests.
0:15
Requests are just people on the Internet
asking for information from our app.
0:18
Once they get to our app, [SOUND] the app
looks at all the routes and
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figures out which function to call.
0:26
A lot of people call these functions
[SOUND] controllers, but
0:27
I prefer the Django way and call [SOUND]
them views.
0:30
The [SOUND] view then sends back a
response, which can be HTML, or JSON, or
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XML, or whatever your specific needs are.
0:36
We call that the request-response cycle.
0:39
If it doesn't make much sense now, don't
worry, we'll be going over it repeatedly.
0:41
Let's go make our app, and a simple
function or view.
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Since Flask is already installed on
Workspaces, as you can see here,
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I don't need to install it and I can
immediately start using it.
0:53
So, I'm gonna make a file up here, and I'm
gonna call it simple_app.py.
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And this is going to hold my app.
1:07
So, let's make an app, right?
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We're gonna make a nice, simple little
app.
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What we have to do first, though, is we
have to import Flask.
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So, from flask, with a lowercase f, we
want to import Flask with an uppercase F.
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If you remember, in Python,
1:23
we always name classes with an uppercase
letter, or almost always.
1:26
You're supposed to always.
1:31
Anyway, so Flask here with a capital F is
a class.
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That's how we know that.
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So now we need to make an app instance.
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So, what we're gonna do is we're gonna
make it to where our app is named,
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whatever our current namespace is.
1:44
And namespaces are a somewhat complicated
area in Python, or they can be.
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What we're gonna do, though, is we're
gonna do this app equals flask and
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we're gonna pass in this magic variable
called dunder name, __name__.
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Dunders on both sides of the name.
2:01
And what this means is use whatever our
current namespace is.
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So, if we run this file with like Python
simple_app.py,
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then the namespace is dunder main, which
means it's being run directly.
2:13
If we were to import simple_app.py into
another file,
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then our namespace will be simple_app.
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So, it's just a way of mean, saying,
always refer to yourself.
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Then we're going to run our app.
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And we're gonna say debug equals True cuz
we want,
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anytime we make changes, we want Flask to
auto-restart.
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And then just for Treehouse because we're
gonna,
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we have a new special little thing over
here in the corner.
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We need to specify a port and a host, so
our port is gonna be 8000, and
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what the port means is this is the
software port to listen on.
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Think of it has having, like, a bunch of
different doors or
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this is like saying which telephone
number, kind of, to call on.
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It's closer to having a bunch of different
doors on a house,
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which door is it gonna be at.
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And then our host, which is like which
house is it on the street,
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is going to be 0.0.0.0, four 0s with dots
between them.
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And that means listen on all addresses
that can get to here.
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So, we're gonna save that and let's see if
this runs.
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Let's give it a try.
3:30
So what we're gonna do, we're going to
come down here to our console and
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we're going to do python simple_app.py.
3:36
All right, so you see here, it says it's
running on our 0s and
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colon 8000, and it's restarting with a
reloader.
3:44
So, we're gonna come up here to this
little eye.
3:48
And this may be the first time you've seen
this.
3:51
This is a pretty new feature.
3:52
And we're gonna say we wanna preview this
on port 80.
3:54
Now, we could use any of these numbers,
but we wanna use port 8000.
3:57
And you can see, we get this 404.
4:01
And that's fine because we haven't told
there to be anything there.
4:05
So, it doesn't know what it's doing,
right?
4:09
We've got this, this, like, no route.
4:13
Okay.
4:16
So, let's let's give it a route.
4:16
Because we haven't created any, so we need
to create some.
4:19
All right.
So, before we do the app.run,
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this is where we get to define our routes.
4:26
So let's make a function called index, and
we're just gonna return a string.
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We're gonna return Hello from Treehouse.
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'Kay?
4:38
Now, this is just a function.
4:39
This isn't a view yet.
4:40
I mean it is, but it's really not.
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It's really just a function.
4:45
What makes this is a view is by giving it
a route.
4:46
And we give it a route by decorating it
with this function called route, and
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then we have to specify what the route is.
4:55
So we're just going to use forward slash,
which, if we look,
4:57
let's see if we can make this its own
window.
5:02
We can, sweet.
5:07
If we look at the URL here,
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we see that we're technically just at this
forward slash.
5:10
So, that's where we're going, and now
we've got Hello from Treehouse.
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So there is Hello from Treehouse.
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This is, I said this was a decorator.
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So, what is a decorator?
5:24
Well, a decorator is a function that wraps
around another function and
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lets you do things to the function.
5:30
So what we've done is we've said, hey,
take this index function and register it
5:32
with our app as the route, forward slash,
just the single forward slash.
5:37
So, we've added this route, added this
function, and
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we get our Hello from Treehouse, so that's
pretty awesome.
5:47
All right, we're done with everything.
5:50
Oh wait, no, that's not nearly enough.
5:53
In the next video, let's look at pulling
information out of the URL.
5:55
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