In the previous articles on the Python decorator series, we have learnt decorators, how they work and to implement a simple function based decorator and a class based decorator and decorator that supports parameters. In this article, we will use flask's before_request and after_request decorator to measure time taken for a request to complete.

import time
from flask import Flask, request, jsonify, current_app, g as app_ctx

app = Flask(__name__)


@app.before_request
def logging_before():
    # Store the start time for the request
    app_ctx.start_time = time.perf_counter()


@app.after_request
def logging_after(response):
    # Get total time in milliseconds
    total_time = time.perf_counter() - app_ctx.start_time
    time_in_ms = int(total_time * 1000)
    # Log the time taken for the endpoint 
    current_app.logger.info('%s ms %s %s %s', time_in_ms, request.method, request.path, dict(request.args))
    return response


@app.get('/')
def home():
    # artificial delay
    time.sleep(1.3)
    return jsonify({'Hello': 'World!!'})


@app.get('/slow-request')
def slow_request():
    # artificial delay
    time.sleep(5)
    return jsonify({'msg': 'slow request'})


if __name__ == '__main__':
    app.run(debug=True)

Logs from console

[2021-05-16 11:43:32,177] INFO : 1304 ms GET / {}
[2021-05-16 11:43:41,822] INFO : 5003 ms GET /slow-request {}

How this works

• On Flask application startup, typically when you run python app.py, Flask registers the functions logging_before and logging_after to the flask's hooks registry
• From then, On receiving a web request flask executes the logging_before function and executes the actual code inside the api code and then logging_after gets executed finally.
• All of these methods can have a shared local state variables in specific to these web request using from flask g as app_ctx
• logging_before saves current time using time.perf_counter() as start_time
• logging_after finds the difference from start_time and logs the message

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In the next article, we will implement various kinds decorator recipes. Stay tuned for upcoming articles. Subscribe to the newsletter and Connect with me on twitter to get my future articles.