Serve file to browser from python (flask) webservice

Question

I have a python webservice that is suppose to receive a GET request from the browser, writes some data into a csv file and serves it back to the browser.

I am struggling with this last step. How can I serve the file back to the browser? Is there a way to do it without creating or keeping the csv file on the server?

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

        alldata = []

        while len(new_data) > 0:
                new_data = api.timeline(max_id=oldest)
                alldata.extend(new_data)
                oldest = alldata[-1].id - 1    
        outdata = [[info.id_str] for data in alldata]

        #write the csv
        with open('data.csv', 'wb') as f:
                writer = csv.writer(f)
                writer.writerows(outdata)
        pass

if __name__ == '__main__':
  app.run(host = app.config['HOST'], port = app.config['PORT'])

You have to use a generator, as described in flask.pocoo.org/docs/0.10/patterns/streaming or you are using a StringIO (or one of the new classes in the io module in Python 3) instead of the file. — Klaus D.
– Klaus D., Commented Apr 21, 2015 at 16:39

nathancahill · Accepted Answer · 2015-04-21 17:00:01Z

1

Instead of writing the file to disk, you can just return it like this:

from flask import make_response

outdata = ""

for data in alldata:
    outdata += ",".join(data) + "\n"

response = make_response(outdata)
response.headers["Content-Disposition"] = "attachment; filename=data.csv"

return response

Alternatively, if you do want to write the file to disk, you can use send_from_directory:

return send_from_directory('my_app', 'data.csv')

answered Apr 21, 2015 at 17:00

nathancahill

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