I am very new to Python / Flask / Javascript, and would appreciate it if someone could help me with this.
I am trying to pass a string value from Javascript back to Python but it does not seem to work. My code is as follows:
Javascript (partial code):
var bounds = '8.3,9,34.3,15.9';
$.post("/receiver", {
bbox_bounds: bounds
});
In Python:
from flask import Flask, request
#Create the Flask app
app = Flask(__name__)
#app.route('/receiver', methods = ['POST'])
def receiver():
bbounds = request.form('bbox_bounds')
print "Bounds: " + bbounds
return bbounds
if __name__ == '__main__':
app.run(port=5000)
Sorry, the above is bad, but I am really a beginner. Thank you.
Change this line,
bbounds = request.form('bbox_bounds')
to
bbounds =request.form['bbox_bounds']
Refer to the Flask Quickstart guide for more detailed examples - http://flask.pocoo.org/docs/1.0/quickstart/#routing
Also issues as such can be easily caught and fixed if you look into your logs.
Related
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 %}
I'm at a beginner at coding and i'm stuck at the final closing :|
i'm using python 2.7
this is my serever.py
from flask import Flask, render_template,request,jsonify
import requests
import json
import new
app = Flask(__name__)
#serve homepage
#app.route('/', methods=["GET","POST"])
def homepage():
return render_template('page2.html')
#app.route('/page3.html', methods=["POST"])
def result_matchup():
h= request.form['h']
a= request.form['a']
l= request.form['l']
p= request.form['p']
result = json.dumps(new.calc(h,a,l,p))
return render_template('page3.html',result=result)
if __name__ == "__main__":
app.run(debug=True)
when i ask for return result for checking myself, this is the output:
{"f": 197.1, "k": 196}
this is my page3.html:
<!DOCTYPE html>
<html>
<head>
</head>
<body>
<center><h1>Final = {{f}}</h1></center>
</body>
</html>
the output for all this is
"Final = "
,while I expect for Final = 197.1.
what am I doing wrong? any help?
thanks!
I assume new.calc returns a dictionary. No need to use json.dumps to stringify that before passing to your template. So instead try:
result = new.calc(h,a,l,p)
result should now be a dictionary, with the keys 'f' and 'k'
Therefor in the template you should access this dictionary, as you would in python:
<center><h1>Final = {{result['f']}}</h1></center>
I would also advise using a later version of python since 2.7 is unsupported now, and making this change early will prevent you having to make already written code, 3.x compatible later.
Two suggestions:
You serialize your result as JSON writing result = json.dumps(new.calc(h,a,l,p)). However, you should directly pass a Python object to render_template. In fact, that's one of the strengths of Jinja templating: You do not need to pass JSON, but you can handle Python objects directly. So just write result = new.calc(h,a,l,p).
Second, within the Jinja template, you have to access the objects as you passed them through your render_template function. In your case, <center><h1>Final = {{result['f]}}</h1></center> should do the job.
I created a website with HTML/CSS. I also used Javascript for events (click on button, ...).
Now I want to connect a Python script with it and more importantly, return the results from my Python functions to my website and display (use) them there.
Consider something like this: I have a website with an input field and a button. If you click on the button, a Python script should run which returns if the input is an odd or even number (of course you don't need Python for this specific case, but that's what I want to do).
From my research I believe Flask is the library to be used for this, but I really don't know how to do it. I found very few examples. I would really appreciate if someone could implement the above example or tell me how to do it exactly.
I know there are already some questions about that concept here online, but as I said, with very few examples.
You're right about Flask being a good solution for this and there are examples and tutorials everywhere. If what you want is just to run a specific function on a button press and get something back in javascript, I've put a quick example is below.
# app.py
from flask import Flask, render_template
from flask import jsonify
app = Flask(__name__)
# Display your index page
#app.route("/")
def index():
return render_template('index.html')
# A function to add two numbers
#app.route("/add")
def add():
a = request.args.get('a')
b = request.args.get('b')
return jsonify({"result": a+b})
if __name__ == "__main__":
app.run(host='0.0.0.0', port=80)
This can then be run with python app.py and make sure your index.html is in the same directory. Then you should be able to go to http://127.0.0.1/ and see your page load.
This implements a function which adds two numbers, this can be called in your javascript by calling http://127.0.0.1/add?a=10&b=20. This should then return {"result": 30}.
You can grab this in your javascript using the code below and place this code in your buttons on click callback.
let first = 10;
let second = 20;
fetch('http://127.0.0.1/add?a='+first+'&b='+second)
.then((response) => {
return response.json();
})
.then((myJson) => {
console.log("When I add "+first+" and "+second+" I get: " + myJson.result);
});
This should be the barebone basics, but once you can submit data to Flask and get data back, you now have an interface to run things in Python.
Edit: Full Front-end example
https://jsfiddle.net/4bv805L6/
I really appreciate time spent on this answer. But the answer did not help me in the way I needed it. At that point I had no clue what to do, but since thenbI figured it out some time ago and I thought I should share my solution here:
That's app.py:
from flask import Flask, render_template, request
app = Flask(__name__)
#app.route('/stick', methods=['GET', 'POST'])
def stick():
if request.method == 'POST':
result = request.form['string1'] + request.form['string2']
return render_template('index.html', result=result)
else:
return render_template('index.html')
if __name__ == "__main__":
app.run()
And that's index.html (put in the folder templates):
<!DOCTYPE html>
<html>
<body>
<h3> Stick two strings </h3>
<form action="{{ url_for('stick') }}" method="post">
<input type="text" name="string1">
<input type="text" name="string2">
<input type="submit" value="Go!">
<p id="result"></p>
</form>
<script>
document.getElementById("result").innerHTML = "{{result}}"
</script>
</body>
</html>
In the terminal, type in python app.py and it should work.
So I'm creating a python app that counts detected objects using OpenCV then passing the counter variable to Flask server using the following HTTP post request:
requests.post('http://127.0.0.1:5000', json = {'count': count})
, the flask sever receives the variable then pass it to a JavaScript within the html template, here is the code of flask server:
app = Flask(__name__)
#app.route("/",methods=['GET', 'POST'])
def index():
content = request.get_json(silent=True)
if content :
cnt = content.get('count') #get JSON from OpenCV every time the count is updated
print cnt # here it prints the variable to the cmd and show me the count update
return render_template("test.html", cnt = cnt); #here the value is passed as zero ?!
if __name__ == "__main__":
app.run(debug=True)
and when I run the 'test.html' template it only show me the 'cnt' variable = 0, although I'm getting the updated value constantly from my OpenCV code to my flask server.
here is the script part of my 'test.html'
<p>People count: <span id="counti"></span></p>
<script>
var countn = '{{cnt}}';
document.getElementById('counti').innerHTML = countn
</script>
I want my 'count' variable to pass smoothly from OpenCV and receive into my Javascript to be able to make my web-app able to make decisions based on the count of objects observed by OpenCV.
What is the optimal way to do this ?
I really appreciate your help!
This is my first dive into Flask + Jinja, but I've used HandlebarsJS a lot in the past, so I know this is possible but I'm not sure how to pull this off with Flask:
I'm building an app: a user enters a string, which is processed via python script, and the result is ajax'd back to the client/Jinja template.
I can output the result using $("body").append(response) but this would mean I need to write some nasty html within the append.
Instead, I'd like to render another template once the result is processed, and append that new template in the original template.
Is this possible?
My python:
from flask import Flask, render_template, request, jsonify
from script import *
app = Flask(__name__)
#app.route('/')
def index():
return render_template('index.html')
#app.route('/getColors')
def add_colors():
user = request.args.get("handle", 0, type = str)
return jsonify(
avatar_url = process_data(data)
)
if __name__ == '__main__':
app.run()
There is no rule about your ajax routes having to return JSON, you can return HTML exactly like you do for your regular routes.
#app.route('/getColors')
def add_colors():
user = request.args.get("handle", 0, type = str)
return render_template('colors.html',
avatar_url=process_data(data))
Your colors.html file does not need to be a complete HTML page, it can be the snippet of HTML that you want the client to append. So then all the client needs to do is append the body of the ajax response to the appropriate element in the DOM.