flask: `@after_this_request` not working

Question

I want to delete a file after the user downloaded a file which was created by the flask app.

For doing so I found this answer on SO which did not work as expected and raised an error telling that after_this_request is not defined.

Due to that I had a deeper look into Flask's documentation providing a sample snippet about how to use that method. So, I extended my code by defining a after_this_request function as shown in the sample snippet.

Executing the code resp. running the server works as expected. However, the file is not removed because @after_this_request is not called which is obvious since After request ... is not printed to Flask's output in the terminal:

#!/usr/bin/env python3
# coding: utf-8


import os
from operator import itemgetter
from flask import Flask, request, redirect, url_for, send_from_directory, g
from werkzeug.utils import secure_filename

UPLOAD_FOLDER = '.'
ALLOWED_EXTENSIONS = set(['csv', 'xlsx', 'xls'])

app = Flask(__name__)
app.config['UPLOAD_FOLDER'] = UPLOAD_FOLDER


def allowed_file(filename):
    return '.' in filename and \
           filename.rsplit('.', 1)[1] in ALLOWED_EXTENSIONS


def after_this_request(func):
    if not hasattr(g, 'call_after_request'):
        g.call_after_request = []
    g.call_after_request.append(func)
    return func


@app.route('/', methods=['GET', 'POST'])
def upload_file():
    if request.method == 'POST':
        if 'file' not in request.files:
            flash('No file part')
            return redirect(request.url)
        file = request.files['file']
        if file.filename == '':
            flash('No selected file')
            return redirect(request.url)
        if file and allowed_file(file.filename):
            filename = secure_filename(file.filename)
            filepath = os.path.join(app.config['UPLOAD_FOLDER'], filename)
            file.save(filepath)

            @after_this_request
            def remove_file(response):
                print('After request ...')
                os.remove(filepath)
                return response

            return send_from_directory('.', filename=filepath, as_attachment=True)

    return '''
    <!doctype html>
    <title>Upload a file</title>
    <h1>Uplaod new file</h1>
    <form action="" method=post enctype=multipart/form-data>
      <p><input type=file name=file>
         <input type=submit value=Upload>
    </form>
    '''


if __name__ == '__main__':
    app.run(host='0.0.0.0', port=8080, debug=True)

What do I miss here? How can I ensure calling the function following to the @after_this_request decorator in order to delete the file after it was downloaded by the user?

Note: Using Flask version 0.11.1

score 7 · Answer 1 · edited Mar 24 '21 at 13:26

7

Just import after_this_request from flask, you don't need to modify after_request or create a hook.

from flask import after_this_request

@after_this_request
def remove_file(response):
    print('After request ...')
    os.remove(filepath)
    return response

edited Mar 24 '21 at 13:26

Jean-François Corbett

37,420
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answered Aug 22 '17 at 20:23

user3167654

263
1
4
9

Martijn Pieters · Accepted Answer · 2018-12-01T10:26:15.763

Make sure to import the decorator from flask.after_this_request. The decorator is new in Flask 0.9.

If you are using Flask 0.8 or older, then there is no specific after this request functionality. There is only a after every request hook, which is what the snippet coopts to handle per-request call-backs.

So unless you are using Flask 0.9 or newer you need to implement the documented hook yourself:

@app.after_request
def per_request_callbacks(response):
    for func in getattr(g, 'call_after_request', ()):
        response = func(response)
    return response

So that hook is run after each and every request, and looks for a list of hooks to call in g.call_after_request. The after_this_request decorator registers a function there.

flask: `@after_this_request` not working

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