In Flask, how do I store a user submitted file temporarily to manipulate it and return it back?

Issue

So I’ve been working on a Flask application where the user submits a file to a form, the server takes it and manipulates it, then returns the edited file back to the user. I am new to Flask and web dev in general, so bear with me. I have already set up the website with the form and a filefield, but Im not exactly sure how I can get the data from the file. Do i have to store it on the server? If I do, do I have to delete after im done?

Here is what I’ve got so far in my routes

@app.route('/mysite', methods=['post', 'get'])
def mysite():
    form = mysiteform()

    if request.method == 'POST' and form.validate():
        file = form.file.data.read()
        filename = secure_filename(file.filename)
    return render_template('mysite.html', title = 'hello world!', form=form)

Solution

In Flask official documentation site, there is a file uploader example as below:

@app.route('/', methods=['GET', 'POST'])
def upload_file():
    if request.method == 'POST':
        # check if the post request has the file part
        if 'file' not in request.files:
            flash('No file part')
            return redirect(request.url)
        file = request.files['file']
        # If the user does not select a file, the browser submits an
        # empty file without a filename.
        if file.filename == '':
            flash('No selected file')
            return redirect(request.url)
        if file and allowed_file(file.filename):
            filename = secure_filename(file.filename)
            file.save(os.path.join(app.config['UPLOAD_FOLDER'], filename))
            return redirect(url_for('download_file', name=filename))
    return '''
    <!doctype html>
    <title>Upload new File</title>
    <h1>Upload new File</h1>
    <form method=post enctype=multipart/form-data>
      <input type=file name=file>
      <input type=submit value=Upload>
    </form>
    '''

Here is how you can get the file content: file = request.files['file'] and of course you can do further manipulation on the file.

Here is how you can save the file file.save(os.path.join(app.config['UPLOAD_FOLDER'], filename)). It’s really up to you if you want to save the file and return the file later or just modify it in memory and return it immediately.

Answered By – nngeek

This Answer collected from stackoverflow, is licensed under cc by-sa 2.5 , cc by-sa 3.0 and cc by-sa 4.0

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