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 %}
So this is embarrassing. I've got an application that I threw together in Flask and for now it is just serving up a single static HTML page with some links to CSS and JS. And I can't find where in the documentation Flask describes returning static files. Yes, I could use render_template but I know the data is not templatized. I'd have thought send_file or url_for was the right thing, but I could not get those to work. In the meantime, I am opening the files, reading content, and rigging up a Response with appropriate mimetype:
import os.path
from flask import Flask, Response
app = Flask(__name__)
app.config.from_object(__name__)
def root_dir(): # pragma: no cover
return os.path.abspath(os.path.dirname(__file__))
def get_file(filename): # pragma: no cover
try:
src = os.path.join(root_dir(), filename)
# Figure out how flask returns static files
# Tried:
# - render_template
# - send_file
# This should not be so non-obvious
return open(src).read()
except IOError as exc:
return str(exc)
#app.route('/', methods=['GET'])
def metrics(): # pragma: no cover
content = get_file('jenkins_analytics.html')
return Response(content, mimetype="text/html")
#app.route('/', defaults={'path': ''})
#app.route('/<path:path>')
def get_resource(path): # pragma: no cover
mimetypes = {
".css": "text/css",
".html": "text/html",
".js": "application/javascript",
}
complete_path = os.path.join(root_dir(), path)
ext = os.path.splitext(path)[1]
mimetype = mimetypes.get(ext, "text/html")
content = get_file(complete_path)
return Response(content, mimetype=mimetype)
if __name__ == '__main__': # pragma: no cover
app.run(port=80)
Someone want to give a code sample or url for this? I know this is going to be dead simple.
In production, configure the HTTP server (Nginx, Apache, etc.) in front of your application to serve requests to /static from the static folder. A dedicated web server is very good at serving static files efficiently, although you probably won't notice a difference compared to Flask at low volumes.
Flask automatically creates a /static/<path:filename> route that will serve any filename under the static folder next to the Python module that defines your Flask app. Use url_for to link to static files: url_for('static', filename='js/analytics.js')
You can also use send_from_directory to serve files from a directory in your own route. This takes a base directory and a path, and ensures that the path is contained in the directory, which makes it safe to accept user-provided paths. This can be useful in cases where you want to check something before serving the file, such as if the logged in user has permission.
from flask import send_from_directory
#app.route('/reports/<path:path>')
def send_report(path):
return send_from_directory('reports', path)
Do not use send_file or send_static_file with a user-supplied path. This will expose you to directory traversal attacks. send_from_directory was designed to safely handle user-supplied paths under a known directory, and will raise an error if the path attempts to escape the directory.
If you are generating a file in memory without writing it to the filesystem, you can pass a BytesIO object to send_file to serve it like a file. You'll need to pass other arguments to send_file in this case since it can't infer things like the file name or content type.
If you just want to move the location of your static files, then the simplest method is to declare the paths in the constructor. In the example below, I have moved my templates and static files into a sub-folder called web.
app = Flask(__name__,
static_url_path='',
static_folder='web/static',
template_folder='web/templates')
static_url_path='' removes any preceding path from the URL (i.e.
the default /static).
static_folder='web/static' to serve any files found in the folder
web/static as static files.
template_folder='web/templates' similarly, this changes the
templates folder.
Using this method, the following URL will return a CSS file:
<link rel="stylesheet" type="text/css" href="/css/bootstrap.min.css">
And finally, here's a snap of the folder structure, where flask_server.py is the Flask instance:
You can also, and this is my favorite, set a folder as static path so that the files inside are reachable for everyone.
app = Flask(__name__, static_url_path='/static')
With that set you can use the standard HTML:
<link rel="stylesheet" type="text/css" href="/static/style.css">
I'm sure you'll find what you need there: http://flask.pocoo.org/docs/quickstart/#static-files
Basically you just need a "static" folder at the root of your package, and then you can use url_for('static', filename='foo.bar') or directly link to your files with http://example.com/static/foo.bar.
EDIT: As suggested in the comments you could directly use the '/static/foo.bar' URL path BUT url_for() overhead (performance wise) is quite low, and using it means that you'll be able to easily customise the behaviour afterwards (change the folder, change the URL path, move your static files to S3, etc).
You can use this function :
send_static_file(filename)
Function used internally to send static
files from the static folder to the browser.
app = Flask(__name__)
#app.route('/<path:path>')
def static_file(path):
return app.send_static_file(path)
What I use (and it's been working great) is a "templates" directory and a "static" directory. I place all my .html files/Flask templates inside the templates directory, and static contains CSS/JS. render_template works fine for generic html files to my knowledge, regardless of the extent at which you used Flask's templating syntax. Below is a sample call in my views.py file.
#app.route('/projects')
def projects():
return render_template("projects.html", title = 'Projects')
Just make sure you use url_for() when you do want to reference some static file in the separate static directory. You'll probably end up doing this anyways in your CSS/JS file links in html. For instance...
<script src="{{ url_for('static', filename='styles/dist/js/bootstrap.js') }}"></script>
Here's a link to the "canonical" informal Flask tutorial - lots of great tips in here to help you hit the ground running.
http://blog.miguelgrinberg.com/post/the-flask-mega-tutorial-part-i-hello-world
A simplest working example based on the other answers is the following:
from flask import Flask, request
app = Flask(__name__, static_url_path='')
#app.route('/index/')
def root():
return app.send_static_file('index.html')
if __name__ == '__main__':
app.run(debug=True)
With the HTML called index.html:
<!DOCTYPE html>
<html>
<head>
<title>Hello World!</title>
</head>
<body>
<div>
<p>
This is a test.
</p>
</div>
</body>
</html>
IMPORTANT: And index.html is in a folder called static, meaning <projectpath> has the .py file, and <projectpath>\static has the html file.
If you want the server to be visible on the network, use app.run(debug=True, host='0.0.0.0')
EDIT: For showing all files in the folder if requested, use this
#app.route('/<path:path>')
def static_file(path):
return app.send_static_file(path)
Which is essentially BlackMamba's answer, so give them an upvote.
For angular+boilerplate flow which creates next folders tree:
backend/
|
|------ui/
| |------------------build/ <--'static' folder, constructed by Grunt
| |--<proj |----vendors/ <-- angular.js and others here
| |-- folders> |----src/ <-- your js
| |----index.html <-- your SPA entrypoint
|------<proj
|------ folders>
|
|------view.py <-- Flask app here
I use following solution:
...
root = os.path.join(os.path.dirname(os.path.abspath(__file__)), "ui", "build")
#app.route('/<path:path>', methods=['GET'])
def static_proxy(path):
return send_from_directory(root, path)
#app.route('/', methods=['GET'])
def redirect_to_index():
return send_from_directory(root, 'index.html')
...
It helps to redefine 'static' folder to custom.
app = Flask(__name__, static_folder="your path to static")
If you have templates in your root directory, placing the app=Flask(name) will work if the file that contains this also is in the same location, if this file is in another location, you will have to specify the template location to enable Flask to point to the location
So I got things working (based on #user1671599 answer) and wanted to share it with you guys.
(I hope I'm doing it right since it's my first app in Python)
I did this -
Project structure:
server.py:
from server.AppStarter import AppStarter
import os
static_folder_root = os.path.join(os.path.dirname(os.path.abspath(__file__)), "client")
app = AppStarter()
app.register_routes_to_resources(static_folder_root)
app.run(__name__)
AppStarter.py:
from flask import Flask, send_from_directory
from flask_restful import Api, Resource
from server.ApiResources.TodoList import TodoList
from server.ApiResources.Todo import Todo
class AppStarter(Resource):
def __init__(self):
self._static_files_root_folder_path = '' # Default is current folder
self._app = Flask(__name__) # , static_folder='client', static_url_path='')
self._api = Api(self._app)
def _register_static_server(self, static_files_root_folder_path):
self._static_files_root_folder_path = static_files_root_folder_path
self._app.add_url_rule('/<path:file_relative_path_to_root>', 'serve_page', self._serve_page, methods=['GET'])
self._app.add_url_rule('/', 'index', self._goto_index, methods=['GET'])
def register_routes_to_resources(self, static_files_root_folder_path):
self._register_static_server(static_files_root_folder_path)
self._api.add_resource(TodoList, '/todos')
self._api.add_resource(Todo, '/todos/<todo_id>')
def _goto_index(self):
return self._serve_page("index.html")
def _serve_page(self, file_relative_path_to_root):
return send_from_directory(self._static_files_root_folder_path, file_relative_path_to_root)
def run(self, module_name):
if module_name == '__main__':
self._app.run(debug=True)
By default folder named "static" contains all static files
Here's a code sample:
<link href="{{ url_for('static', filename='vendor/bootstrap/css/bootstrap.min.css') }}" rel="stylesheet">
Use redirect and url_for
from flask import redirect, url_for
#app.route('/', methods=['GET'])
def metrics():
return redirect(url_for('static', filename='jenkins_analytics.html'))
This servers all files (css & js...) referenced in your html.
One of the simple way to do. Cheers!
demo.py
from flask import Flask, render_template
app = Flask(__name__)
#app.route("/")
def index():
return render_template("index.html")
if __name__ == '__main__':
app.run(debug = True)
Now create folder name called templates.
Add your index.html file inside of templates folder
index.html
<!DOCTYPE html>
<html>
<head>
<title>Python Web Application</title>
</head>
<body>
<div>
<p>
Welcomes You!!
</p>
</div>
</body>
</html>
Project Structure
-demo.py
-templates/index.html
The issue I had was related to index.html files not being served for directories when using static_url_path and static_folder.
Here's my solution:
import os
from flask import Flask, send_from_directory
from flask.helpers import safe_join
app = Flask(__name__)
static = safe_join(os.path.dirname(__file__), 'static')
#app.route('/')
def _home():
return send_from_directory(static, 'index.html')
#app.route('/<path:path>')
def _static(path):
if os.path.isdir(safe_join(static, path)):
path = os.path.join(path, 'index.html')
return send_from_directory(static, path)
Thought of sharing.... this example.
from flask import Flask
app = Flask(__name__)
#app.route('/loading/')
def hello_world():
data = open('sample.html').read()
return data
if __name__ == '__main__':
app.run(host='0.0.0.0')
This works better and simple.
All the answers are good but what worked well for me is just using the simple function send_file from Flask. This works well when you just need to send an html file as response when host:port/ApiName will show the output of the file in browser
#app.route('/ApiName')
def ApiFunc():
try:
return send_file('some-other-directory-than-root/your-file.extension')
except Exception as e:
logging.info(e.args[0])```
The simplest way is create a static folder inside the main project folder. Static folder containing .css files.
main folder
/Main Folder
/Main Folder/templates/foo.html
/Main Folder/static/foo.css
/Main Folder/application.py(flask script)
Image of main folder containing static and templates folders and flask script
flask
from flask import Flask, render_template
app = Flask(__name__)
#app.route("/")
def login():
return render_template("login.html")
html (layout)
<!DOCTYPE html>
<html>
<head>
<title>Project(1)</title>
<link rel="stylesheet" href="/static/styles.css">
</head>
<body>
<header>
<div class="container">
<nav>
<a class="title" href="">Kamook</a>
<a class="text" href="">Sign Up</a>
<a class="text" href="">Log In</a>
</nav>
</div>
</header>
{% block body %}
{% endblock %}
</body>
</html>
html
{% extends "layout.html" %}
{% block body %}
<div class="col">
<input type="text" name="username" placeholder="Username" required>
<input type="password" name="password" placeholder="Password" required>
<input type="submit" value="Login">
</div>
{% endblock %}
The URL for a static file can be created using the static endpoint as following:
url_for('static', filename = 'name_of_file')
<link rel="stylesheet" href="{{url_for('static', filename='borders.css')}}" />
By default, flask use a "templates" folder to contain all your template files(any plain-text file, but usually .html or some kind of template language such as jinja2 ) & a "static" folder to contain all your static files(i.e. .js .css and your images).
In your routes, u can use render_template() to render a template file (as I say above, by default it is placed in the templates folder) as the response for your request. And in the template file (it's usually a .html-like file), u may use some .js and/or `.css' files, so I guess your question is how u link these static files to the current template file.
If you are just trying to open a file, you could use app.open_resource(). So reading a file would look something like
with app.open_resource('/static/path/yourfile'):
#code to read the file and do something
In the static directory, create templates directory inside that directory add all the html file create separate directory for css and javascript as flask will treat or recognize all the html files which are inside the template directory.
static -
|_ templates
|_ css
|_javascript
|_images
This is what worked for me:
import os
from flask import Flask, render_template, send_from_directory
app = Flask(__name__)
root = os.path.join(os.path.dirname(os.path.abspath(__file__)), "whereyourfilesare")
#app.route('/', methods=['GET'])
def main(request):
path = request.path
if (path == '/'):
return send_from_directory(root, 'index.html')
else:
return send_from_directory(root, path[1:])
In my case, i needed all the files from a static folder to be accessible by the user, as well as i needed to use templates for some of my html files, so that common html code could be placed in the template and code gets reused. Here is how i achieved both of them together:
from flask import Flask, request, render_template
from flask.json import JSONEncoder
app = Flask(__name__, template_folder='static')
#app.route('/<path:path>')
def serve_static_file(path):
# In my case, only html files are having the template code inside them, like include.
if path.endswith('.html'):
return render_template(path)
# Serve all other files from the static folder directly.
return app.send_static_file(path)
And all of my files are kept under static folder, which is parallel to main flask file.
For example, to return an Adsense file I have used:
#app.route('/ads.txt')
def send_adstxt():
return send_from_directory(app.static_folder, 'ads.txt')
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.