python - Writing a CSV from Flask framework

Question

This question already has answers here:

Create and download a CSV file from a Flask view (2 answers)

Closed 1 year ago.

I have no problems writing a CSV outside of the Flask framework. But when I try to write it from Flask, it writes to the CSV, but only on one line.

Here is the template I'm following

@app.route('/download')
def download():
    csv = """"REVIEW_DATE","AUTHOR","ISBN","DISCOUNTED_PRICE"
"1985/01/21","Douglas Adams",0345391802,5.95
"1990/01/12","Douglas Hofstadter",0465026567,9.95
"1998/07/15","Timothy ""The Parser"" Campbell",0968411304,18.99
"1999/12/03","Richard Friedman",0060630353,5.95
"2004/10/04","Randel Helms",0879755725,4.50"""
    response = make_response(csv)
    response.headers["Content-Disposition"] = "attachment; filename=books.csv"
    return response

This writes the CSV perfectly, but when I try with my code, I get one long row.

My code:

@app.route('/download')
def post(self):

    # lots of code

    csvList.append([all,my,data,goes,here])

    csvList = str(re.sub('\[|\]','',str(csvList)))  # convert to a string; remove brackets

    response = make_response(csvList)
    response.headers['Content-Disposition'] = "attachment; filename=myCSV.csv"
    return response

My output:

Nashville Physician Service Ce,Treasury Specialist,Brentwood,TN,[phone],La Petite Academy,Afternoon Teacher Aide,Goodlettsville,TN,[phone],Nashville Physician Service Ce,Denial Resolution Specialist,Brentwood,TN,[phone]

Thanks.

EDIT: I tried just about all the answers and they worked for the most part, but I chose vectorfrog's because it fit with what I was trying to accomplish.

Answer 1

I did something like this recently, I found that I needed to first place the csv into a StringIO and then return the StringIO. If you want the csv to be a download, here's what I did:

import StringIO
import csv
from flask import make_response

@app.route('/download')
def post(self):
    si = StringIO.StringIO()
    cw = csv.writer(si)
    cw.writerows(csvList)
    output = make_response(si.getvalue())
    output.headers["Content-Disposition"] = "attachment; filename=export.csv"
    output.headers["Content-type"] = "text/csv"
    return output

Answer 2

You need to add newlines. Anyway, your method of making csvs (printing the list and removing brackets from it) is not the best way to do it. Try this instead:

csvList = '\n'.join(','.join(row) for row in csvList)

Or use the csv module:

import io, csv

dest = io.StringIO()
writer = csv.writer(dest)

for row in csvList:
    writer.writerow(row)

# Now dest is a file-like object containing your csv

Answer 3

One alternative::

from flask import Flask, make_response
import pyexcel as pe
import StringIO # py2.7, for python3, please use import io

app = Flask(__name__)

data = [
    ["REVIEW_DATE","AUTHOR","ISBN","DISCOUNTED_PRICE"],
    ["1985/01/21","Douglas Adams",'0345391802',5.95],
    ["1990/01/12","Douglas Hofstadter",'0465026567',9.95],
    ["1998/07/15","Timothy \"The Parser\" Campbell",'0968411304',18.99],
    ["1999/12/03","Richard Friedman",'0060630353',5.95],
    ["2004/10/04","Randel Helms",'0879755725',4.50]
]

@app.route('/download')
def download():
    sheet = pe.Sheet(data)
    io = StringIO.StringIO()
    sheet.save_to_memory("csv", io)
    output = make_response(io.getvalue())
    output.headers["Content-Disposition"] = "attachment; filename=export.csv"
    output.headers["Content-type"] = "text/csv"
    return output

if __name__ == "__main__":
    app.debug=True
    app.run()

Another alternative is to use Flask-Excel:

from flask import Flask, make_response
from flask.ext import excel

app = Flask(__name__)

data = [
    ["REVIEW_DATE","AUTHOR","ISBN","DISCOUNTED_PRICE"],
    ["1985/01/21","Douglas Adams",'0345391802',5.95],
    ["1990/01/12","Douglas Hofstadter",'0465026567',9.95],
    ["1998/07/15","Timothy \"The Parser\" Campbell",'0968411304',18.99],
    ["1999/12/03","Richard Friedman",'0060630353',5.95],
    ["2004/10/04","Randel Helms",'0879755725',4.50]
]

@app.route('/download')
def download():
    output = excel.make_response_from_array(data, 'csv')
    output.headers["Content-Disposition"] = "attachment; filename=export.csv"
    output.headers["Content-type"] = "text/csv"
    return output

if __name__ == "__main__":
    app.debug=True
    app.run()

Answer 4

Since csv is just a plain text format you shoud make shure that new line separator - \n is present at the end of every line you have

Answer 5

I'm not quite sure I understand your objective, but you can try the str.join() method. So, if you wanted to make a quick CSV output from a list of lists:

csvList= [['1', '2', '3'], ['4', '5', '6'], ['asdf', '7', 'eight']]
csvStrings= []
for csvLine in csvList:
    csvStrings += [",".join(csvLine)]
print "\n".join(csvStrings)