flask: show request time in template

app.py

import time

from flask import Flask, request, g, render_template

app = Flask(__name__)
app.config['DEBUG'] = True

@app.before_request
def before_request():
    g.request_start_time = time.time()
    g.request_time = lambda: "%.5fs" % (time.time() - g.request_start_time)

@app.route("/")
def index():
    t = request.values.get('t', 0)
    time.sleep(float(t)) #just to show it works...
    return render_template("index.html")

if __name__ == "__main__":
    app.run(use_debugger=True, use_reloader=True)

index.html

Rendered in {{ g.request_time() }}

output.txt

$ curl http://127.0.0.1:5000/
Rendered in 0.00100s

$ curl http://127.0.0.1:5000/?t=1
Rendered in 1.00106s

$ curl http://127.0.0.1:5000/?t=2
Rendered in 2.00111s

$ curl http://127.0.0.1:5000/?t=10
Rendered in 10.00057s

could you explain this a bit? what is the line g.request_time = lambda: "%.5fs" % (time.time() - g.request_start_time) doing exactly? i don't understand how you are coming up with a time if you are not doing anything during after_request

@chrickso, that line just creates a function that returns the time since before_request was called. The function is called later when the template is rendered (in index.html) which happens after the request has completed.

Given the lambda can capture the scope variables, you could simplify this to:

@app.before_request
def before_request():
    request_start_time = time.time()
    g.request_time = lambda: "%.5fs" % (time.time() - request_start_time)

unless, of course you want the request_start_time to be queryable separately

Great, didn't know there's such thing as before_request and after_request, thank you :)

Cool solution, just one small thing to pay attention to when your measuring performance:

If you call {{ g.request_time() }} at the start of your html template, and then do a whole bunch of rendering, the time will be off. I had up to a factor of 20x speed difference, and couldn't figure out why, and this was the reason. My solution was to put this small snippet at the button of the template:

...

<p id="request_time_paragraph"></p>

do_some_heavy_rendering()
<script>
document.getElementById('request_time_paragraph').innerHTML = "{{ g.request_time() }}"
</script>

You’ll want to use time.monotonic() for correctness :)

Otherwise, you end up with weird negative page rendering times during leap seconds :)

I got jinja2.exceptions.TemplateNotFound

please resolve this

@mallikharjuna160003 To resolve this error just create a directory "templates" and put the required html files in.