Python flask upload file but do not save and use

Question

My code currently takes in a file, and saves it to a preset directory, but is it possible to just use the file (read the file) and not save it?

@app.route('/', methods=['GET', 'POST'])
def upload_file():
    if request.method == 'POST':
        file = request.files['file']
        if file and allowed_file(file.filename):
            filename = secure_filename(file.filename)
            file.save(os.path.join(app.config['UPLOAD_FOLDER'], filename))
            return "yatta"
        else:
            return "file not allowed"

    return render_template("index.html")

I have tried both

file.read() and file.stream.read() but the return value of that is empty. I verify that the file exists in the uploaded directory and see that the file is not empty.

possible duplicate of [Read file data without saving it in Flask](http://stackoverflow.com/questions/20015550/read-file-data-without-saving-it-in-flask) — ForceBru, Feb 10 '15 at 17:41
@ForceBru I tried using file.read() but the return value of that is empty, when I verify the saved file, I can see that the file's not empty. — Stupid.Fat.Cat, Feb 10 '15 at 17:49
have you tried using python's [tempfile](https://docs.python.org/2/library/tempfile.html)? — corvid, Feb 10 '15 at 17:49
@Stupid.Fat.Cat, you've seen I marked ur question as duplicate. See the link, please. Maybe it'll help you. — ForceBru, Feb 10 '15 at 17:52
@corvid I have not, I suspect that it won't work since file.stream itself is empty — Stupid.Fat.Cat, Feb 10 '15 at 17:52
I've replied to the same kind of question here: http://stackoverflow.com/a/42405115/7578261 — Dimitry Miles, Feb 23 '17 at 01:01

addicted · Accepted Answer · 2017-10-10T04:18:46.493

I know that this is very outdated but for the sake of people landing here for similar inquiry, here it is if you want to save AND read your file after wards. Seems like Werkzeug's FileStorage class (which is the class to handle uploaded file in Flask) pointing to end of file after every action (saving or reading). So we have to move the pointer up to the beginning of the file before doing any subsequent action. I am using python's pandas in my answer below because I usually read csv into dataframe.

import pandas as pd

@app.route('/', methods=['GET', 'POST'])
    def upload_file():
        if request.method == 'POST':
            file = request.files['file']
            if file and allowed_file(file.filename):
                filename = secure_filename(file.filename)
                file.save(os.path.join(app.config['UPLOAD_FOLDER'], filename))

                ## snippet to read code below
                file.stream.seek(0) # seek to the beginning of file
                myfile = file.file # will point to tempfile itself
                dataframe = pd.read_csv(myfile)
                ## end snippet

                return "yatta"
            else:
                return "file not allowed"

        return render_template("index.html")

invaluable - file.stream.seek(0) is a hidden gem - huge thanks! — jtlz2, Nov 10 '17 at 12:01
`file.stream.seek(0)` before `file.save(secure_filename(file.filename))` fixed my problem with empty file saving. Thanxs alot! — berrymorr, Aug 11 '20 at 17:49

score 3 · Answer 2 · answered Dec 05 '16 at 21:44

Make sure you're not saving the file with file.save() before you call file.read().

So, your function would be:

@app.route('/', methods=['GET', 'POST'])
def upload_file():
    if request.method == 'POST':
        file = request.files['file']
        if file and allowed_file(file.filename):
            filename = secure_filename(file.filename)
            contents = file.read()
            # do something with file contents
            file.save(os.path.join(app.config['UPLOAD_FOLDER'], filename))
            return "yatta"
        else:
            return "file not allowed"

    return render_template("index.html")

Hope this helps!

Python flask upload file but do not save and use

2 Answers2