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Flask Basics

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Flash Messages

5:28 with Kenneth Love

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 %}.

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    Quite often, we need to send a message to our user, but 0:00
    we don't need it to be anything permanent, 0:02
    just a message that shows up until they refresh the page or go to a new one. 0:04
    We call these flash messages in the world of Flask, and, 0:08
    they are super easy to set up and use. 0:10
    All right. 0:12
    So, we need to, we want to send some messages to the user, be like, hey! 0:13
    We save your stuff. 0:17
    So, we're gonna do that here in app.py, and, 0:19
    to do that we have to import the flash function, which is part of Flask. 0:23
    So, let's add that here, all right. 0:30
    So, there's our flash function. 0:33
    And, flash messages actually use the users session, and, 0:37
    sessions in Flask are cryptographically signed, which is awesome, but, that means 0:42
    that we have to provide a, a secret key for Flask to use to sign our messages. 0:47
    so, do not try to type what I'm typing, it really doesn't matter, 0:55
    secret keys are completely random, you want them to be as random as possible, 1:00
    and they're better off it they're longer, so just random stuff. 1:05
    You wanna just type all sorts of things, and then save, mine's not insanely random, 1:10
    but it's random enough, so type out a bunch of gibberish. 1:17
    All right, so now we need to go down here and update our save method, 1:21
    because saving is where the, well, save is where the saving happens, right? 1:25
    So, that's where we want to give that information back to the user, we want to 1:30
    be like, hey by the way, your stuff has been saved, which is pretty cool. 1:35
    So the way that we do that is we call the flash method, so 1:42
    we're going to call flash, and then we're going to pass it a message, and 1:46
    we're going to do save changes. 1:50
    Actually, lets just say, alright, that looks 1:54
    awesome, you can, of course, put in there whatever you want. 2:01
    So now we have a problem though, just a little tiny one, 2:06
    tiny problem, don't worry about it. 2:10
    Which is that we don't have anything that prints out the flash messages. 2:12
    So, let's go and add that, cuz right now, fy, if I sit here and I hit update. 2:16
    The flash happened, 2:23
    it's there, but you can't see it, because we're not printing it out anywhere. 2:23
    So let's go add that, let's go to layout and right here before this 2:27
    block content is where I want to add in the flash messages. 2:33
    So, I'm going to call this div class, wrap no bottom, 2:39
    and messages, and then inside here, 2:46
    I'm gonna use with messages equal to get flashed messages. 2:51
    So with, says inside this next little block because were gonna end this 2:59
    an end with, so inside here, have this variable called messages, 3:05
    and make it equal to the value of this function get_flashed_messages. 3:12
    So get_flashed_messages gets all of our flash messages. 3:16
    I know, crazy, huh? 3:20
    So if there are messages. 3:22
    [BLANK_AUDIO] 3:25
    Then we want to do ul class equals flashes, 3:29
    and we're going to do for message and messages, 3:35
    we're going to do an LI where we just print out the message. 3:41
    All right. And we end our with and we end our, or 3:50
    our if and our with, and then we have our block of content, all right. 3:53
    So, let's see what's going on down here, 3:59
    looks like my app restarted, so I'm gonna do python_app.by. 4:01
    There we go, I got it running again, and let's hit Update. 4:04
    Oh, all right, so I got something printed out, but I can't read it. 4:12
    So, you know what? 4:20
    We've got this background color. 4:21
    So, let's let's print that out, so, we'll come in here and we'll do 4:24
    b g saves dot get colors and if we don't have 4:31
    a color then lets do, yellow, cause I kind of like how that yellow one looks. 4:37
    Alright, so we'll hit update. 4:44
    Alright, that looks awesome, and lets see if I change it to purple. 4:47
    Hey, check that out. 4:51
    Orange, there we go, take it a minute. 4:57
    Okay. 4:59
    So that prints this out, so, flash message, 5:00
    messages only persist until the next time that the page is viewed. 5:03
    So if I hit refresh, Cmd+R, then you notice that we don't get 5:08
    the Flash message again, but if I save the form, then we get it all over again. 5:12
    Sending messages back to your users is a very handy tool as you build a web app. 5:18
    Making sure your users understand what's going on, 5:22
    will make them happier to use your software, and more comfortable with it. 5:24

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