Introduction

I was writing a simple python application in Flask. So I wanted to add asynchronous processing. However, there were some points that I got stuck in, so I wrote an article. One thing I can say first is that asynchronous processing in python may be better with a non-Flask framework. When I was googled, I felt that other frameworks had more information.

Execution content

The user types two numbers into the text box and presses a button. The server side performs the operation of adding the two numbers asynchronously and returns the response to the user immediately.

Execution environment

os: Windows10 redis Redis-x64-3.0.504.msi

python 3.5.6 (Anaconda) Flask==1.1.1 celery==3.1.25 redis==2.10.6

Execution procedure

--Run "python sample.py" in Anaconda Prompt. --Run "celery -A sample.celery worker -l info" in Anaconda Prompt. --Access localhost: 9000, type a number in the text box and press Execute Calculation.

--As a result, a response is returned immediately. Confirm that the calculation result is displayed in Anaconda Prompt that executed celery.

Stumble point

--Since the versions of celery and redis are compatible, first check these.

--Check if redis is running on localhost: 6397.

--Check if the function to be processed asynchronously is registered in the task of celery. (Can be confirmed on the terminal where "celery -A sample.celery worker -l info" is executed)

in conclusion

It's easy, but I've attached sample.py and main.html below. It works with these two files. I also attached the URL of the site I referred to.

If you have any questions or mistakes, please comment.

Source code

`sample.py`


# coding=utf-8
from flask import Flask, render_template, request

#Flask app preparation
app = Flask("sample")

# this is a part of celery property to use in Flask
from celery import Celery
def make_celery(app):
    celery = Celery(
        app.import_name,
        backend=app.config['CELERY_RESULT_BACKEND'],
        broker=app.config['CELERY_BROKER_URL']
    )
    celery.conf.update(app.config)

    class ContextTask(celery.Task):
        def __call__(self, *args, **kwargs):
            with app.app_context():
                return self.run(*args, **kwargs)

    celery.Task = ContextTask
    return celery

# update flask config to use celery
app.config.update(
    CELERY_BROKER_URL='redis://localhost:6379',
    CELERY_RESULT_BACKEND='redis://localhost:6379'
)
celery = make_celery(app)

@celery.task()
def add(a, b):
    print(a + b)
    return a + b

@app.route('/', methods=["GET", "POST"])
def sample():

    #Processing at POST
    if request.method == 'POST':
        return render_template(
            'main.html',  #HTML file to display
            )

    #Processing at the time of GET
    else:
        return render_template(
            'main.html',  #HTML file to display
            )

@app.route('/celery', methods=["POST"])
def celery_test():

    if request.method == 'POST':
        a = int(request.form["num_one"])
        b = int(request.form["num_two"])
        result = add.delay(a,b)
        return render_template(
                'main.html',  #HTML file to display
                )

if __name__ == '__main__':
    app.run(debug=True, host='0.0.0.0', port=9000)

`main.html`


<!DOCTYPE html>
<html lang="ja">
  <head>
    <meta charset="utf-8"/>
    <title>Sample</title>
    <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css">
  </head>
 
  <body>      
    <div class="container">
      <div class="jumbotron">
        <h1>
          <p align="center">
            <font size="10">Flask asynchronous processing</font>
          </p>
        </h1>
      </div>

      <form class="" method="post" action="/celery" enctype="multipart/form-data">
        <div class="container" style="text-align: center;">
          <input type="number" name="num_one">  +  
          <input type="number" name="num_two">
        </div>

        <div class="button_wrapper" style="text-align: center;">
          <button type="submit" class="btn btn-lg btn-success" style="margin-top: 50px; ">Calculation execution</button>
        </div>

      </form>
    </div> 

  </body>
</html>

References

Install Redis for Windows and try it out http://kageura.hatenadiary.jp Flask official https://flask.palletsprojects.com/en/1.0.x/patterns/celery/ python – Unable to launch Celery Worker https://codeday.me/jp/qa/20190525/900758.html celery AttributeError: 'str' object has no attribute 'items' django Day14 http://www.programmersought.com/article/8120463251/

[PYTHON] Celery asynchronous processing in Flask