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If we want to give the user a message that's only visible for the current load of the page, we use the `flash()` function. Just another handy tidbit from the Flask.
New Terms
flash(): This function stores a message in the session that will self-destruct after the response is returned.
get_flashed_messages(): This function gets all of the flash messages stored in the session.
app.secret_key: This configuration attribute stores the secret key that all messages are cryptographically signed with.
{% with %}: The Flask template version of Python's with block. Let's you temporarily define a variable. Must be closed with {% endwith %}.
Quite often, we need to send a message to
our user, but
0:00
we don't need it to be anything permanent,
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just a message that shows up until they
refresh the page or go to a new one.
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We call these flash messages in the world
of Flask, and,
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they are super easy to set up and use.
0:10
All right.
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So, we need to, we want to send some
messages to the user, be like, hey!
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We save your stuff.
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So, we're gonna do that here in app.py,
and,
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to do that we have to import the flash
function, which is part of Flask.
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So, let's add that here, all right.
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So, there's our flash function.
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And, flash messages actually use the users
session, and,
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sessions in Flask are cryptographically
signed, which is awesome, but, that means
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that we have to provide a, a secret key
for Flask to use to sign our messages.
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so, do not try to type what I'm typing, it
really doesn't matter,
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secret keys are completely random, you
want them to be as random as possible,
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and they're better off it they're longer,
so just random stuff.
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You wanna just type all sorts of things,
and then save, mine's not insanely random,
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but it's random enough, so type out a
bunch of gibberish.
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All right, so now we need to go down here
and update our save method,
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because saving is where the, well, save is
where the saving happens, right?
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So, that's where we want to give that
information back to the user, we want to
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be like, hey by the way, your stuff has
been saved, which is pretty cool.
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So the way that we do that is we call the
flash method, so
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we're going to call flash, and then we're
going to pass it a message, and
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we're going to do save changes.
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Actually, lets just say, alright, that
looks
1:54
awesome, you can, of course, put in there
whatever you want.
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So now we have a problem though, just a
little tiny one,
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tiny problem, don't worry about it.
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Which is that we don't have anything that
prints out the flash messages.
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So, let's go and add that, cuz right now,
fy, if I sit here and I hit update.
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The flash happened,
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it's there, but you can't see it, because
we're not printing it out anywhere.
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So let's go add that, let's go to layout
and right here before this
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block content is where I want to add in
the flash messages.
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So, I'm going to call this div class, wrap
no bottom,
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and messages, and then inside here,
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I'm gonna use with messages equal to get
flashed messages.
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So with, says inside this next little
block because were gonna end this
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an end with, so inside here, have this
variable called messages,
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and make it equal to the value of this
function get_flashed_messages.
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So get_flashed_messages gets all of our
flash messages.
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I know, crazy, huh?
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So if there are messages.
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[BLANK_AUDIO]
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Then we want to do ul class equals
flashes,
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and we're going to do for message and
messages,
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we're going to do an LI where we just
print out the message.
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All right.
And we end our with and we end our, or
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our if and our with, and then we have our
block of content, all right.
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So, let's see what's going on down here,
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looks like my app restarted, so I'm gonna
do python_app.by.
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There we go, I got it running again, and
let's hit Update.
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Oh, all right, so I got something printed
out, but I can't read it.
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So, you know what?
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We've got this background color.
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So, let's let's print that out, so, we'll
come in here and we'll do
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b g saves dot get colors and if we don't
have
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a color then lets do, yellow, cause I kind
of like how that yellow one looks.
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Alright, so we'll hit update.
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Alright, that looks awesome, and lets see
if I change it to purple.
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Hey, check that out.
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Orange, there we go, take it a minute.
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Okay.
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So that prints this out, so, flash
message,
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messages only persist until the next time
that the page is viewed.
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So if I hit refresh, Cmd+R, then you
notice that we don't get
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the Flash message again, but if I save the
form, then we get it all over again.
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Sending messages back to your users is a
very handy tool as you build a web app.
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Making sure your users understand what's
going on,
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will make them happier to use your
software, and more comfortable with it.
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