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How to inject a variable into <img src='VARIABLE'>

If I place one of the dictionary values(i.e "https://....) directly into <img src, the image will render properly. Using the variable 'musician'(which contains "https://...) will yield an empty properly formatted frame with a broken image logo.
musician_dict = {
'g': 'https://media.stubhubstatic.com/stubhub-catalog/d_defaultLogo.jpg/t_f-fs-0fv,q_auto:low,f_auto,c_fill,$w_280_mul_3,$h_180_mul_3/performer/404807/gvwionkcazusra2wbkuu',
'p': 'https://cdn.britannica.com/18/161418-050-811E4CBE/McCoy-Tyner.jpg?w=400&h=300&c=crop'
}
# The website starts with a main page
#app.route("/")
def piano_or_guitar_game():
musician = random.choice(list(musician_dict.values()))
return "<h1>pIANO player or gUITAR player(q to quit)</h1>" \
"<img src=musician width=500>"

You're sending it back as a string literal. With Flask, you'd usually do something like:
return render_template("index.html", picture=musician)
and then in your templates folder, you would have:
<img src={{picture}} width=500>
See Flask's blog tutorial.

Python yield clear output [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 %}

jinja2: including script, replacing {{variable}} and json encoding the result

I'm attempting to build a json document using Jinja2 and the document has a nested script. The script contains {{<variables>}} that I need to replace along with non-json characters. Therefore, the script needs to be json-escaped afterwards using json.dumps().
str = '{
"nestedScript" : {% include "scripts/sc.ps1" | json %}
}'
The escape function isn't enough, since the finished product contains characters that are valid HTML, but not JSON.
I'm thinking something along the lines of:
str = '{
"nestedScript" : {{ include("scripts/sc.ps1") | json}} %}
}'
using some a custom filter or something, but I can't seem to write the include function such that it also does variable replacement in the script. This is my script so far that I am including as a global:
Complete example
Folder structure:
.
└── templates
├── test.json
└── scripts
    └── script.ps1
template-file:
test.json = '{
"nestedScript" : {{ include("scripts/script.ps1") | json}}
}'
Script:
loader = jinja2.FileSystemLoader("templates")
env = jinja2.Environment(loader=self.loader)
template = env.get_template("test.json")
template.render({
'service_name': 'worker',
'context_name': 'googlesellerratings',
})
result:
{
"nestedScript" : "echo {{service_name}}"
}

Solved this in a way that feels a little hackish, so I'd love some feedback. When instantiating my class, I defined a global function called include_script:
loader = jinja2.FileSystemLoader(templates_folder)
env = inja2.Environment(loader=self.loader)
env.globals['include_script'] = render_script_func(env)
the render_script_func returns a function that retrieves the context from the environment and uses it to render the file I referenced:
def render_script_func(env):
def render_script(name):
ctx = env.globals['context']
tmpl = env.get_template(name)
raw = tmpl.render(ctx)
return json.dumps(raw)
return render_script
Now, before rendering, all one has to do, is add the context for the rendering to the global context object:
template = env.get_template(template_name)
template.environment.globals["context"] = ctx
renderedData = template.render(ctx)
And when a template uses {{ include_script("path/to/script") }} the script is both rendered and then json encoded.
Still feels a bit wrong, but so be it.

Given the (incomplete) example it seems you are searching the filter tag.
First the script in a form that's actually runnable and defines a json filter in terms of json.dumps():
import json
import jinja2
loader = jinja2.FileSystemLoader('templates')
env = jinja2.Environment(loader=loader)
env.filters['json'] = json.dumps
template = env.get_template('test.json')
print(
template.render({
'service_name': 'worker',
'context_name': 'googlesellerratings',
})
)
The missing PowerShell script with characters that cause trouble if used as is in JSON ("):
echo "{{service_name}}"
Now the solution for the test.json template:
{
"nestedScript" : {% filter json %}{% include "scripts/script.ps1" %}{% endfilter %}
}
And finally the printed result:
{
"nestedScript" : "echo \"worker\""
}

Dynamically update image using Python Flask AJAX

I have 1 very simple web application I am building right now but am very new to flask and jinja (and web development as a whole actually).
I have a watch folder, which will be getting an image sent to it via ftp on a pulse for ever. This wtch folder will only ever have one image in. Every 1 minute, the old image is replaced by a new image, with a new timestamp.
I would like to dynamically update the page, (and displayed timestamp) on a pulse as well, without having to reload any banners or static images that I will add later. I only want to update the following two lines out of the "Channels.Jinja" sample to follow.
<br>{{screenshot_datetime}}<br/>
<img src={{screenshot_location}} width="100%"/>
Channels.Jinja
<!DOCTYPE HTML>
<html>
<head>
<title>Training</title>
</head>
<body bgcolor=white>
<div id=main>
<br>Date and Time of Screenshot <br/>
<br>{{screenshot_datetime}}<br/>
<img src={{screenshot_location}} width="100%"/>
</div>
<div id='test'>
<p>
<script>
var myVar=setInterval(function(){get_image()},1000);
function get_image() {
$.ajax({
type: 'GET',
cache: false,
url: 'get_data',
success: function({{data}}) {
$('img').attr('src', data);
}
});
}
</script>
</p>
</div>
</body>
</html>
Channels.py
def render_channel_route(cr):
static_folder = os.path.join('static',cr)
file_list = os.listdir(static_folder)
channel_files = [f for f in file_list if f.startswith(cr)]
if not channel_files :
logger.error('Could not find image file for Channel. File should start with {0}'.format(cr))
abort(404)
img = os.path.join(static_folder,file_list[0])
ts = get_time_from_filename(file_list[0],cr)
return render_template('Channels.jinja',screenshot_datetime=time.strftime('%c',ts),screenshot_location=img)
#app.route('/channel01-10')
def first_tab():
return render_channel_route('channel01-10')
#app.route('/get_data', methods=['GET'])
def get_data():
return render_template('Channels.jinja',
screenshot_datetime=time.strftime('%c',ts),screenshot_location=img)
Im at a loss, Ive been bumbling around for a while now. Any and all advice is welcome! I am seeing a 304 response upon refresh, but not even the timer i am trying to put on it is working. Pardon sloppy code, highly volatile code is getting changed often -_-

I don't know it there is a "special" way to deal with Ajax using some Flask extension, but in the "normal" Ajax flow first you need to use url_for to put the correct url in your Ajax call and return the data formatted in some way (in my example in JSON) and not to render the template again:
$.ajax({
type: 'GET',
cache: false,
url: "{{ url_for('get_data') }}",
success: function(resp){
$('img').attr('src', resp.url);
$('#sst').html(resp.time);
}
});
So, in your get_data function in your controller you have to get the time and the path again for your image an then return some like this (to fit in my example before):
from flask import json
#app.route('/get_data', methods=['GET'])
def get_data():
#get time and path
time=...
path=...
return json.dumps({time:time,url:path}), 200, {'Content-Type':'application/json'}
Look that I use $('#sst') so you have to put in your HTML:
<br><span id='sst'>{{screenshot_datetime}}</span><br/>

json unicode to string so i can use that in django html page

Edited :
Anybody tell me how to decode the unicode.I just want to print json unicode into my html page i developed. I got the api from heroku api.
pretty much i followed every step correctly. But the output is unicode and that i don`t know how to extract the content and display into my page.
I need to print the content. How to do that ?
my views.py
template_vars['kural'] = json.dumps(thirukural[x])
t = loader.get_template('index.html')
c = Context(template_vars)
#pprint.pprint(c)
return HttpResponse(t.render(c))
Html Page
<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
</head><body>
<p id="p"></p>
<script type="text/javascript">
var t = {{kural|safe}}
var text = eval(t);
var p = document.getElementById("p");
p.innerHTML=t.kural;
</script>
</body></html>
</body>
</html>
It`s currently printed like this
யாதனின் யாதனின் நீங்கியான் நோதல் அதனின் அதனின் இலன்.
but in the heroku api page the sample output printed like this
{
"id": "213",
"kural": "புத்தே ளுலகத்தும் ஈண்டும் பெறலரிதே\n\nஒப்புரவின் நல்ல பிற."
}
You can see that my output doesnt have line breaks that \n . How can i do that ?

The kural variable is a dict, if you want to display kural in your view, I think you need json.
import json
template_vars['kural'] = json.dumps(thirukural[x])

I believe what you'll want to do is change that first line you show of your views code to:
template_vars['kural'] = thirukural[x].encode('ascii', 'xmlcharrefreplace')
That should change everything into HTML entities and it will end up looking something like this:
'உலகம் தழீஇய தொட்பம் மலர்தலும்\n\nகூம்பலும் இல்ல தறிவு.'