Display a ‘loading’ message while a time consuming function is executed in Flask
Question:
I’m still relatively new to Flask, and a bit of a web noob in general, but I’ve had some good results so far. Right now I’ve got a form in which users enter a query, which is given to a function that can take anywhere between 5 and 30 seconds to return a result (looking up data with the Freebase API).
The problem is that I can’t let the user know that their query is loading during this time, as the results page only loads once the function finishes its work. Is there a way I can display a loading message while that’s going on? I found some Javascript that could display a loading message while page elements are still loading, but my waiting period happens before ‘render_template’.
I knocked together some example code, just to demonstrate my situation:
Python:
from flask import Flask
from flask import request
from flask import render_template
import time
app = Flask(__name__)
def long_load(typeback):
time.sleep(5) #just simulating the waiting period
return "You typed: %s" % typeback
@app.route('/')
def home():
return render_template("index.html")
@app.route('/', methods=['POST'])
def form(display=None):
query = request.form['anything']
outcome = long_load(query)
return render_template("done.html", display=outcome)
if __name__ == '__main__':
#app.debug = True
app.run()
Excerpt from index.html:
<body>
<h3>Type anything:</h3>
<p>
<form action="." method="POST">
<input type="text" name="anything" placeholder="Type anything here">
<input type="submit" name="anything_submit" value="Submit">
</form>
</p>
</body>
Excerpt from done.html:
<body>
<h3>Results:</h3>
<p>
{{ display }}
</p>
</body>
Any help would be greatly appreciated, I hope this example helps.
Answers:
This can be done by using a div that contains a ‘loading gif’ image. When the submit button is clicked, the div is displayed using javascript.
To implement this, you can take a look at this website: http://web.archive.org/web/20181023063601/http://www.netavatar.co.in/2011/05/31/how-to-show-a-loading-gif-image-while-a-page-loads-using-javascript-and-css/
Add this to your index.html or js file (I’m assuming you have jQuery here, you could use standard javascript of course.):
<script type="text/javascript">// <![CDATA[
function loading(){
$("#loading").show();
$("#content").hide();
}
// ]]></script>
Add this to you html or css file:
div#loading {
width: 35px;
height: 35px;
display: none;
background: url(/static/loadingimage.gif) no-repeat;
cursor: wait;
}
You can get an adequate GIF from http://www.ajaxload.info/. Download and put it into your static folder.
Then change your submission button to call above js function:
<input type="submit" name="anything_submit" value="Submit" onclick="loading();">
and add in a loading and a content div to you base html file:
<body>
<div id="loading"></div>
<div id="content">
<h3>Type anything:</h3>
<p>
<form action="." method="POST">
<input type="text" name="anything" placeholder="Type anything here">
<input type="submit" name="anything_submit" value="Submit" onclick="loading();">
</form>
</p>
</div>
</body>
Now when you click ‘Submit’, the js function should hide your content and display a loading GIF. This will display until your data is processed and flask loads the new page.
I found the purely CSS-dependent loader very useful. It does not depend on external resources:
https://www.w3schools.com/howto/howto_css_loader.asp
This is a bit of an old topic, but I needed to deal with this problem today and came with a solution on my own. I’m running a machine learning model that recieves an image input from the user and does some magic.
Basically this is what I did.
On my index.html file, I called a loading function on my "Submit" button passing the filename, because I was going to use it later:
<form method="post" action="/loading/{{filename}}"
enctype="multipart/form-data">
<input type="submit" value="Submit!">
</form>
On Flask, I created a route just to render the loading screen before doing the time consuming task, also passing the filename ahead:
@app.route('/loading/<filename>', methods=['POST'])
def loading_model(filename):
return render_template ("loading.html", filename=filename)
And then, on loading.html, I render my .gif animation and at the end I redirect the page to the time consuming task function:
<!doctype html>
<head>
<link rel= "stylesheet" type= "text/css" href= "{{url_for('static',filename='styles/main.css') }}">
</head>
<div id="preloader">
<div id="status"> </div>
<h1 class="ml13">ANALYZING...</h1>
<script src="https://cdnjs.cloudflare.com/ajax/libs/animejs/2.0.2/anime.min.js> </script>
</div>
<title>Title</title>
<script src="{{url_for('static', filename='main.js')}}"></script>
<script> window.location.replace('/task/{{filename}}'); </script>
And then, final step, back to Flask, call the task function:
@app.route('/task/<filename>', methods=['POST', 'GET'])
def task(filename):
# Do your stuff
return render_template ("results.html")
By doing this, the gif animation will keep playing whilst the function does its job, and then render the results or the next page you want.
You obviously have to edit the css file so that "preloader" and "status" behave like you wish, this is how I used it:
#preloader {
background-color: white;
position: fixed;
top: 0;
bottom: 0;
left: 0;
right: 0;
}
#status {
background-image: url("lalala.gif");
background-repeat: no-repeat;
width: 800px;
height: 600px;
position: absolute;
top: 50%;
left: 50%;
margin-top: -400px;
margin-left: -400px;
}
It worked out for me.
Brilliant @jka.ne but confusing situation.
I only needed to introduce the loading gif while a button was clicked.
My solution was:
<script type="text/javascript">
function loading(){
$("#loading").show();
window.location.href="../target_html";
}
</script>
Then:
<button type="button" class="xxx" onclick="loading();">Run</button>
Finally:
<div id="loading"></div>
I’m still relatively new to Flask, and a bit of a web noob in general, but I’ve had some good results so far. Right now I’ve got a form in which users enter a query, which is given to a function that can take anywhere between 5 and 30 seconds to return a result (looking up data with the Freebase API).
The problem is that I can’t let the user know that their query is loading during this time, as the results page only loads once the function finishes its work. Is there a way I can display a loading message while that’s going on? I found some Javascript that could display a loading message while page elements are still loading, but my waiting period happens before ‘render_template’.
I knocked together some example code, just to demonstrate my situation:
Python:
from flask import Flask
from flask import request
from flask import render_template
import time
app = Flask(__name__)
def long_load(typeback):
time.sleep(5) #just simulating the waiting period
return "You typed: %s" % typeback
@app.route('/')
def home():
return render_template("index.html")
@app.route('/', methods=['POST'])
def form(display=None):
query = request.form['anything']
outcome = long_load(query)
return render_template("done.html", display=outcome)
if __name__ == '__main__':
#app.debug = True
app.run()
Excerpt from index.html:
<body>
<h3>Type anything:</h3>
<p>
<form action="." method="POST">
<input type="text" name="anything" placeholder="Type anything here">
<input type="submit" name="anything_submit" value="Submit">
</form>
</p>
</body>
Excerpt from done.html:
<body>
<h3>Results:</h3>
<p>
{{ display }}
</p>
</body>
Any help would be greatly appreciated, I hope this example helps.
This can be done by using a div that contains a ‘loading gif’ image. When the submit button is clicked, the div is displayed using javascript.
To implement this, you can take a look at this website: http://web.archive.org/web/20181023063601/http://www.netavatar.co.in/2011/05/31/how-to-show-a-loading-gif-image-while-a-page-loads-using-javascript-and-css/
Add this to your index.html or js file (I’m assuming you have jQuery here, you could use standard javascript of course.):
<script type="text/javascript">// <![CDATA[
function loading(){
$("#loading").show();
$("#content").hide();
}
// ]]></script>
Add this to you html or css file:
div#loading {
width: 35px;
height: 35px;
display: none;
background: url(/static/loadingimage.gif) no-repeat;
cursor: wait;
}
You can get an adequate GIF from http://www.ajaxload.info/. Download and put it into your static folder.
Then change your submission button to call above js function:
<input type="submit" name="anything_submit" value="Submit" onclick="loading();">
and add in a loading and a content div to you base html file:
<body>
<div id="loading"></div>
<div id="content">
<h3>Type anything:</h3>
<p>
<form action="." method="POST">
<input type="text" name="anything" placeholder="Type anything here">
<input type="submit" name="anything_submit" value="Submit" onclick="loading();">
</form>
</p>
</div>
</body>
Now when you click ‘Submit’, the js function should hide your content and display a loading GIF. This will display until your data is processed and flask loads the new page.
I found the purely CSS-dependent loader very useful. It does not depend on external resources:
https://www.w3schools.com/howto/howto_css_loader.asp
This is a bit of an old topic, but I needed to deal with this problem today and came with a solution on my own. I’m running a machine learning model that recieves an image input from the user and does some magic.
Basically this is what I did.
On my index.html file, I called a loading function on my "Submit" button passing the filename, because I was going to use it later:
<form method="post" action="/loading/{{filename}}"
enctype="multipart/form-data">
<input type="submit" value="Submit!">
</form>
On Flask, I created a route just to render the loading screen before doing the time consuming task, also passing the filename ahead:
@app.route('/loading/<filename>', methods=['POST'])
def loading_model(filename):
return render_template ("loading.html", filename=filename)
And then, on loading.html, I render my .gif animation and at the end I redirect the page to the time consuming task function:
<!doctype html>
<head>
<link rel= "stylesheet" type= "text/css" href= "{{url_for('static',filename='styles/main.css') }}">
</head>
<div id="preloader">
<div id="status"> </div>
<h1 class="ml13">ANALYZING...</h1>
<script src="https://cdnjs.cloudflare.com/ajax/libs/animejs/2.0.2/anime.min.js> </script>
</div>
<title>Title</title>
<script src="{{url_for('static', filename='main.js')}}"></script>
<script> window.location.replace('/task/{{filename}}'); </script>
And then, final step, back to Flask, call the task function:
@app.route('/task/<filename>', methods=['POST', 'GET'])
def task(filename):
# Do your stuff
return render_template ("results.html")
By doing this, the gif animation will keep playing whilst the function does its job, and then render the results or the next page you want.
You obviously have to edit the css file so that "preloader" and "status" behave like you wish, this is how I used it:
#preloader {
background-color: white;
position: fixed;
top: 0;
bottom: 0;
left: 0;
right: 0;
}
#status {
background-image: url("lalala.gif");
background-repeat: no-repeat;
width: 800px;
height: 600px;
position: absolute;
top: 50%;
left: 50%;
margin-top: -400px;
margin-left: -400px;
}
It worked out for me.
Brilliant @jka.ne but confusing situation.
I only needed to introduce the loading gif while a button was clicked.
My solution was:
<script type="text/javascript">
function loading(){
$("#loading").show();
window.location.href="../target_html";
}
</script>
Then:
<button type="button" class="xxx" onclick="loading();">Run</button>
Finally:
<div id="loading"></div>