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How to make Flask run function in HTML and print out the result on the same page?

I've been trying to use my script that I previously written to turn Arabic numerals to Roman. User inputs numbers and my script turns them to Roman ones. Script runs fine, but me trying to embed it to a webpage is not working as intended. I googled solutions to that and everyone tell I need to get the value from a form, which I did:
<form action="toroman" method="POST">
<input type="number" name="arabic" onChange="toroman(this.value)" oninput="toroman(this.value)">
<p>{{ romanfinal }}</p>
</form>
And this is my server.py that should be printing out the number of the same page, but it doesn't do that, instead when I press "Enter" when submitting the value it creates a new page and displays correct answer.
from flask import Flask, render_template, request
app = Flask(__name__)
#app.route("/")
def index():
return render_template("index.html")
#app.route("/toroman", methods=['POST'])
def toroman():
arabic = request.form['arabic']
# some unnecessarily numerous lines of code that basically turn Arabic-system number to Roman system
return romanfinal
if __name__ == "__main__":
app.run(debug=True)
This is like the only time it actually worked, when I try to change it so something else, it just gives me errors. Please tell me what exactly I don't understand about it.

Your toroman(): function should return index.html with the parameter :
#app.route("/toroman", methods=['POST'])
def toroman():
arabic = request.form['arabic']
# some unnecessarily numerous lines of code that basically turn Arabic-system number to Roman system
return render_template("index.html", data = romanfinal)
Then you can use the value data in your HTML top level like that : {{data}}

FLASK
from flask import Flask, render_template, request, jsonify
app = Flask(__name__)
#app.route("/")
def index():
return render_template("index.html")
#app.route("/toroman", methods=['POST'])
def toroman():
arabic = request.data['arabic']
#pass arabic into your translation function
translation = translate()
#return JSON response to AJAX
return jsonify(translation = translation)
if __name__ == "__main__":
app.run(debug=True)
JS
$(document).ready(function(){
document.getElementById('toroman_form').addEventListener('keyup', function() {
$.ajax({
type: 'POST',
url: '/toroman', //flask route to which data is sent
data: $('#arabic').val(), // input field value
contentType:'application/json; charset=utf-8',
dataType: "json",
success: function(data) {
translation = data.translation //response received from flask
$('#translated').text(translation) //display translation in html <p> tag
},
error: function() {
alert("Transaction Failed");
}
});
});
}
HTML
<form id="toroman_form">
<input type="number" id="arabic">
<p id="translated"><!--translation is dislayed here--></p>
</form>

Flask: display newly generated image on webpage while continuing with function?

I have a webpage where the user uploads an image and my python code will make some adjustments to it and do some analysis. I want the newly generated image to be displayed to the user on the webpage as soon as it's generated, and then continue doing the analysis that needs to be done, and then update the webpage with that information. However, I am not sure how to communicate from flask to the webpage halfway through the function (once the new image is generated) that the website can display the newly generated image, as using render_template can only be done at the end of the function.
My python (flask) code is as follows:
#app.route('/uploaded', methods=['GET', 'POST'])
def upload_file():
if request.method == 'POST':
filename = secure_filename(file.filename)
f = request.files['file']
f.save(secure_filename(f.filename))
image = cv2.imread(filename)
im = Image.fromarray(image)
# make some adjustments to the image (not shown here) and then save it...
im.save(os.path.join(app.config['UPLOAD_FOLDER'], 'your_file.jpg'))
# after the new image is generated, display it on the website at {{ place_for_generated_image }}
# do some more analysis, then finally:
return render_template('index.html', analysis = analysis)
HTML is straightforward:
<form action = "http://localhost/uploaded" method = "POST"
enctype = "multipart/form-data">
<input type = "file" name = "file" class="form-control-file">
<input type = "submit" class="btn btn-info" value="Upload Image" button id="uploadfile" onclick="uploadfile()">
</form>
{{ place_for_generated_image }}
{{ analysis }}

You need to use multiple ajax calls to achieve that. Something like the below:
First make a route to handle the image upload
#app.route('/uploaded', methods=['GET', 'POST'])
def upload_file():
if request.method == 'POST':
filename = secure_filename(file.filename)
f = request.files['file']
f.save(secure_filename(f.filename))
image = cv2.imread(filename)
im = Image.fromarray(image)
# make some adjustments to the image (not shown here) and then save it...
im.save(os.path.join(app.config['UPLOAD_FOLDER'], 'your_file.jpg'))
# Here you need to convert your image to a base64 string and return that string to your ajax call
# do some more analysis, then finally:
return 'YOUR BASE64 ENCODED IMAGE STRING'
This route will handle your analysis. Your second nested ajax call will communicate with this route
from flask import Response
#app.route('/analyze', methods=['GET', 'POST'])
def analyze():
# run some analysis
return Response(status=200, response="Anlysis Done")
This what your javascript code should look like. You can place it in a script tag in your template. If you place it in a separate JS file, make sure to look at my comment for the url_for in the second ajax call
$('form').submit(function(e){
e.preventDefault();
$.ajax({
url: $(this).attr('action'),
type: 'POST',
data: $(this).serialize()
}).done(function(res){
// Here you write code that will display the returned base64 image
// from the upload_file route Just update your img tag src to the
// base64 string you received as the response
// SECOND AJAX CALL TO RUN THE ANALYTICS
$.ajax({
url: "{{url_for('analysis')}}", // if this JS code in a separate JS file you will have to declare a URL variable in a script tag in your template as {{url_for}} is only accessible from your template
type: 'POST',
data: 'any data you want to send can be in JSON format'
}).done(function(res){
// analysis is done
})
})
})

Is it possible to provide the user with status reports from Flask during a looping python function? [duplicate]

I have a view that generates data and streams it in real time. I can't figure out how to send this data to a variable that I can use in my HTML template. My current solution just outputs the data to a blank page as it arrives, which works, but I want to include it in a larger page with formatting. How do I update, format, and display the data as it is streamed to the page?
import flask
import time, math
app = flask.Flask(__name__)
#app.route('/')
def index():
def inner():
# simulate a long process to watch
for i in range(500):
j = math.sqrt(i)
time.sleep(1)
# this value should be inserted into an HTML template
yield str(i) + '<br/>\n'
return flask.Response(inner(), mimetype='text/html')
app.run(debug=True)

You can stream data in a response, but you can't dynamically update a template the way you describe. The template is rendered once on the server side, then sent to the client.
One solution is to use JavaScript to read the streamed response and output the data on the client side. Use XMLHttpRequest to make a request to the endpoint that will stream the data. Then periodically read from the stream until it's done.
This introduces complexity, but allows updating the page directly and gives complete control over what the output looks like. The following example demonstrates that by displaying both the current value and the log of all values.
This example assumes a very simple message format: a single line of data, followed by a newline. This can be as complex as needed, as long as there's a way to identify each message. For example, each loop could return a JSON object which the client decodes.
from math import sqrt
from time import sleep
from flask import Flask, render_template
app = Flask(__name__)
#app.route("/")
def index():
return render_template("index.html")
#app.route("/stream")
def stream():
def generate():
for i in range(500):
yield "{}\n".format(sqrt(i))
sleep(1)
return app.response_class(generate(), mimetype="text/plain")
<p>This is the latest output: <span id="latest"></span></p>
<p>This is all the output:</p>
<ul id="output"></ul>
<script>
var latest = document.getElementById('latest');
var output = document.getElementById('output');
var xhr = new XMLHttpRequest();
xhr.open('GET', '{{ url_for('stream') }}');
xhr.send();
var position = 0;
function handleNewData() {
// the response text include the entire response so far
// split the messages, then take the messages that haven't been handled yet
// position tracks how many messages have been handled
// messages end with a newline, so split will always show one extra empty message at the end
var messages = xhr.responseText.split('\n');
messages.slice(position, -1).forEach(function(value) {
latest.textContent = value; // update the latest value in place
// build and append a new item to a list to log all output
var item = document.createElement('li');
item.textContent = value;
output.appendChild(item);
});
position = messages.length - 1;
}
var timer;
timer = setInterval(function() {
// check the response for new data
handleNewData();
// stop checking once the response has ended
if (xhr.readyState == XMLHttpRequest.DONE) {
clearInterval(timer);
latest.textContent = 'Done';
}
}, 1000);
</script>
An <iframe> can be used to display streamed HTML output, but it has some downsides. The frame is a separate document, which increases resource usage. Since it's only displaying the streamed data, it might not be easy to style it like the rest of the page. It can only append data, so long output will render below the visible scroll area. It can't modify other parts of the page in response to each event.
index.html renders the page with a frame pointed at the stream endpoint. The frame has fairly small default dimensions, so you may want to to style it further. Use render_template_string, which knows to escape variables, to render the HTML for each item (or use render_template with a more complex template file). An initial line can be yielded to load CSS in the frame first.
from flask import render_template_string, stream_with_context
#app.route("/stream")
def stream():
#stream_with_context
def generate():
yield render_template_string('<link rel=stylesheet href="{{ url_for("static", filename="stream.css") }}">')
for i in range(500):
yield render_template_string("<p>{{ i }}: {{ s }}</p>\n", i=i, s=sqrt(i))
sleep(1)
return app.response_class(generate())
<p>This is all the output:</p>
<iframe src="{{ url_for("stream") }}"></iframe>

5 years late, but this actually can be done the way you were initially trying to do it, javascript is totally unnecessary (Edit: the author of the accepted answer added the iframe section after I wrote this). You just have to include embed the output as an <iframe>:
from flask import Flask, render_template, Response
import time, math
app = Flask(__name__)
#app.route('/content')
def content():
"""
Render the content a url different from index
"""
def inner():
# simulate a long process to watch
for i in range(500):
j = math.sqrt(i)
time.sleep(1)
# this value should be inserted into an HTML template
yield str(i) + '<br/>\n'
return Response(inner(), mimetype='text/html')
#app.route('/')
def index():
"""
Render a template at the index. The content will be embedded in this template
"""
return render_template('index.html.jinja')
app.run(debug=True)
Then the 'index.html.jinja' file will include an <iframe> with the content url as the src, which would something like:
<!doctype html>
<head>
<title>Title</title>
</head>
<body>
<div>
<iframe frameborder="0"
onresize="noresize"
style='background: transparent; width: 100%; height:100%;'
src="{{ url_for('content')}}">
</iframe>
</div>
</body>
When rendering user-provided data render_template_string() should be used to render the content to avoid injection attacks. However, I left this out of the example because it adds additional complexity, is outside the scope of the question, isn't relevant to the OP since he isn't streaming user-provided data, and won't be relevant for the vast majority of people seeing this post since streaming user-provided data is a far edge case that few if any people will ever have to do.

Originally I had a similar problem to the one posted here where a model is being trained and the update should be stationary and formatted in Html. The following answer is for future reference or people trying to solve the same problem and need inspiration.
A good solution to achieve this is to use an EventSource in Javascript, as described here. This listener can be started using a context variable, such as from a form or other source. The listener is stopped by sending a stop command. A sleep command is used for visualization without doing any real work in this example. Lastly, Html formatting can be achieved using Javascript DOM-Manipulation.
Flask Application
import flask
import time
app = flask.Flask(__name__)
#app.route('/learn')
def learn():
def update():
yield 'data: Prepare for learning\n\n'
# Preapre model
time.sleep(1.0)
for i in range(1, 101):
# Perform update
time.sleep(0.1)
yield f'data: {i}%\n\n'
yield 'data: close\n\n'
return flask.Response(update(), mimetype='text/event-stream')
#app.route('/', methods=['GET', 'POST'])
def index():
train_model = False
if flask.request.method == 'POST':
if 'train_model' in list(flask.request.form):
train_model = True
return flask.render_template('index.html', train_model=train_model)
app.run(threaded=True)
HTML Template
<form action="/" method="post">
<input name="train_model" type="submit" value="Train Model" />
</form>
<p id="learn_output"></p>
{% if train_model %}
<script>
var target_output = document.getElementById("learn_output");
var learn_update = new EventSource("/learn");
learn_update.onmessage = function (e) {
if (e.data == "close") {
learn_update.close();
} else {
target_output.innerHTML = "Status: " + e.data;
}
};
</script>
{% endif %}

Jquery button click to send AJAX request with Flask and Python

I am trying to make a web application that accepts button clicks. The button clicked then sends a specific device, and operation code to the python application which then calls a irsend command using Lirc. This is based off of the source code/instructions from here:
https://github.com/slimjim777/web-irsend
http://randomtutor.blogspot.com/2013/01/web-based-ir-remote-on-raspberry-pi.html
The html for the button is simple and is in "Xbox.html"
<button onclick="clickedOp('Xbox', 'OnOff');"> Power </button>
This launches the js function:
<script>
function clickedOp(device_name, op) {
$.ajax({url:'/' + device_name + '/clicked/' + op});
}
I know that the function is firing on a click event because if i put an alert command in the clickedOp function the alert command runs
the python/flask app looks like this:
from flask import Flask
from flask import render_template
from flask import request, redirect, url_for
BASE_URL = ''
app = Flask(__name__)
#app.route("/")
def menu():
return render_template('menu.html')
#app.route("/<device_name>")
def remote(device_name):
if device_name == "Xbox":
return render_template('Xbox.html')
#app.route("/<device_name>/clicked/<op>")
def clicked(device_id=None, op=None):
return render_template('test.html')
if __name__ == "__main__":
app.run('0.0.0.0', port=80, debug=True)
All of the code up to the ajax request works. going to "/" loads the menu.html template and presents links to different devices, for instance
Xbox
will route to
"/<device_name>"
in the python program and "Xbox.html" is loaded.
Then the button loads and clicking it fires the "clickedOp(device_name, op)" function.
This is where it breaks down. Even though the ajax request routes to
"/<device_name>/clicked/<op>"
the "test.html" page is not loaded
This is the case even though the Flask debugger says that there was a successful GET request(it returns 200) to "/Xbox/clicked/OnOff" (filling in the variables for the example above)
so any ideas why test.html is not being loaded from the ajax request, when it seems that in the source code/tutorial I provided he uses the same ajax method?

You can simply do this with help of AJAX... Here is a example which calls a python function which prints hello without redirecting or refreshing the page.
In app.py put below code segment.
//rendering the HTML page which has the button
#app.route('/json')
def json():
return render_template('json.html')
//background process happening without any refreshing
#app.route('/background_process_test')
def background_process_test():
print "Hello"
return "nothing"
And your json.html page should look like below.
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
<script type=text/javascript>
$(function() {
$('a#test').on('click', function(e) {
e.preventDefault()
$.getJSON('/background_process_test',
function(data) {
console.log(data)
});
});
});
</script>
//button
<div class='container'>
<h3>Test</h3>
<form>
<a href=# id=test><button class='btn btn-default'>Test</button></a>
</form>
</div>
Here when you press the button Test simple in the console you can see "Hello" is displaying without any refreshing.

In the code the template will render and be returned to the jquery Ajax object, which will do nothing with it - it won't render it in the browser. Have you used your browser's developer tools to see if a response is received by the browser - again, if Flask logs HTTP 200 OK then I would imagine the request is being handled correctly. You should also be able to put print statements in your Flask method and see them logged too (I think).

Streaming data with Python and Flask

I can't seem to figure out how to using Flask's streaming. Here's my code:
#app.route('/scans/')
def scans_query():
url_for('static', filename='.*')
def generate():
yield render_template('scans.html')
for i in xrange(50):
sleep(.5)
yield render_template('scans.html', **locals())
return Response(stream_with_context(generate()))
and in my template:
<p>{% i %}</p>
I would like to see a counter on the page that changes every half second. Instead, the closest I've gotten is the page printing out each number on the next line.

To replace existing content on the page you might need javascript i.e., you could send it or make it to make requests for you, use long polling, websockets, etc. There are many ways to do it, here's one that uses server send events:
#!/usr/bin/env python
import itertools
import time
from flask import Flask, Response, redirect, request, url_for
app = Flask(__name__)
#app.route('/')
def index():
if request.headers.get('accept') == 'text/event-stream':
def events():
for i, c in enumerate(itertools.cycle('\|/-')):
yield "data: %s %d\n\n" % (c, i)
time.sleep(.1) # an artificial delay
return Response(events(), content_type='text/event-stream')
return redirect(url_for('static', filename='index.html'))
if __name__ == "__main__":
app.run(host='localhost', port=23423)
Where static/index.html:
<!doctype html>
<title>Server Send Events Demo</title>
<style>
#data {
text-align: center;
}
</style>
<script src="http://code.jquery.com/jquery-latest.js"></script>
<script>
if (!!window.EventSource) {
var source = new EventSource('/');
source.onmessage = function(e) {
$("#data").text(e.data);
}
}
</script>
<div id="data">nothing received yet</div>
The browser reconnects by default in 3 seconds if the connection is lost. if there is nothing more to send the server could return 404 or just send some other than 'text/event-stream' content type in response to the next request. To stop on the client side even if the server has more data you could call source.close().
Note: if the stream is not meant to be infinite then use other techniques (not SSE) e.g., send javascript snippets to replace the text (infinite <iframe> technique):
#!/usr/bin/env python
import time
from flask import Flask, Response
app = Flask(__name__)
#app.route('/')
def index():
def g():
yield """<!doctype html>
<title>Send javascript snippets demo</title>
<style>
#data {
text-align: center;
}
</style>
<script src="http://code.jquery.com/jquery-latest.js"></script>
<div id="data">nothing received yet</div>
"""
for i, c in enumerate("hello"):
yield """
<script>
$("#data").text("{i} {c}")
</script>
""".format(i=i, c=c)
time.sleep(1) # an artificial delay
return Response(g())
if __name__ == "__main__":
app.run(host='localhost', port=23423)
I've inlined the html here to show that there is nothing more to it (no magic). Here's the same as above but using templates:
#!/usr/bin/env python
import time
from flask import Flask, Response
app = Flask(__name__)
def stream_template(template_name, **context):
# http://flask.pocoo.org/docs/patterns/streaming/#streaming-from-templates
app.update_template_context(context)
t = app.jinja_env.get_template(template_name)
rv = t.stream(context)
# uncomment if you don't need immediate reaction
##rv.enable_buffering(5)
return rv
#app.route('/')
def index():
def g():
for i, c in enumerate("hello"*10):
time.sleep(.1) # an artificial delay
yield i, c
return Response(stream_template('index.html', data=g()))
if __name__ == "__main__":
app.run(host='localhost', port=23423)
Where templates/index.html:
<!doctype html>
<title>Send javascript with template demo</title>
<style>
#data {
text-align: center;
}
</style>
<script src="http://code.jquery.com/jquery-latest.js"></script>
<div id="data">nothing received yet</div>
{% for i, c in data: %}
<script>
$("#data").text("{{ i }} {{ c }}")
</script>
{% endfor %}

I think if you're going to use templates like that, you might need to use the stream_template function given here: http://flask.pocoo.org/docs/patterns/streaming/#streaming-from-templates
I didn't test this, but it might look like:
def stream_template(template_name, **context):
app.update_template_context(context)
t = app.jinja_env.get_template(template_name)
rv = t.stream(context)
rv.enable_buffering(5)
return rv
#app.route('/scans/')
def scans_query():
url_for('static', filename='.*')
def generate():
for i in xrange(50):
sleep(.5)
yield i
return Response(stream_template('scans.html', i=generate()))