Tag: BytesIO

In this tutorial I will explain how to turn an array to a csv file. I will show you two ways. One is in memory and the other is to a file.

For both ways you need to import csv and io package.

import csv, io

Way 1 Write (In Memory):

#Create the string buffer
output = io.StringIO()

#Setup the csv writer to write the results to a string buffer
wr = csv.writer(output, delimiter=',', quotechar='"', quoting=csv.QUOTE_MINIMAL)

Way 2 Write (File):

#Crate the file itself in write mode
f = open('filename.csv', 'w')

#Setup the csv writer to write the results to a file.
wr = csv.writer(f, delimiter=',', quotechar='"', quoting=csv.QUOTE_MINIMAL)

Technically both ways have the same setup for the csv writer. Then to write results to the csv writer you then pass an array of values like below.

wr.writerow(['123',5,4,'value'])

To Read the contents of the file or string buffer depends on which way you chose. I show you those ways below.

Way 1 Read (In Memory):

b = bytes(output.getvalue(), 'utf-u')

Way 2 Read (File):

f.close()
file_data = open('filename.csv', 'r').read()

If you want to send the file down using something like flask send_file then you need to convert it to BytesIO.

buffer = BytesIO()
buffer.write(b)
#You must seek to beginning otherwise it won't send anything back.
buffer.seek(0)

Now if you are sending it as a file back to the user and are using something like flask this is how you do that. Pretty straight forward.

return send_file(buffer, mimetype='application/octet-stream', as_attachment=True, attachment_filename='myFile.csv')