Generate the data with csv.writer
and stream the response. Use StringIO to write to an in-memory buffer rather than generating an intermediate file.
import csv
from datetime import datetime
from io import StringIO
from flask import Flask
from werkzeug.wrappers import Response
app = Flask(__name__)
# example data, this could come from wherever you are storing logs
log = [
('login', datetime(2015, 1, 10, 5, 30)),
('deposit', datetime(2015, 1, 10, 5, 35)),
('order', datetime(2015, 1, 10, 5, 50)),
('withdraw', datetime(2015, 1, 10, 6, 10)),
('logout', datetime(2015, 1, 10, 6, 15))
]
@app.route("https://stackoverflow.com/")
def download_log():
def generate():
data = StringIO()
w = csv.writer(data)
# write header
w.writerow(('action', 'timestamp'))
yield data.getvalue()
data.seek(0)
data.truncate(0)
# write each log item
for item in log:
w.writerow((
item[0],
item[1].isoformat() # format datetime as string
))
yield data.getvalue()
data.seek(0)
data.truncate(0)
# stream the response as the data is generated
response = Response(generate(), mimetype="text/csv")
# add a filename
response.headers.set("Content-Disposition", "attachment", filename="log.csv")
return response
If the generate
function will need information from the current request
, it should be decorated with stream_with_context
, otherwise you will get a “working outside request context” error. Everything else remains the same.
from flask import stream_with context
@stream_with_context
def generate():
...