python - How to stream CSV from Flask via sqlalchemy query? -

i'd stream csv flask using technique they describe here:

from flask import response  @app.route('/large.csv') def generate_large_csv():     def generate():         row in iter_all_rows():             yield ','.join(row) + '\n'     return response(generate(), mimetype='text/csv') 

i have query sqlalchemy returns list of purchase objects. i'd write csv, ideally customization on attributes output file.

unfortunately, i'm getting blank csv output currently:

@app.route('/sales_export.csv') @login_required def sales_export():     """ export csv of sales data """     def generate():         count = 0         fieldnames = [             'uuid',             'recipient_name',             'recipient_email',             'shipping_street_address_1',             'shipping_street_address_2',             'shipping_city',             'shipping_state',             'shipping_zip',             'purchaser_name',             'purchaser_email',             'personal_message',             'sold_at'         ]         i, row in enumerate(purchase.query.all()):             if == 0:                 yield fieldnames             csv = ','.join(row) + '\n'             yield csv     return response(generate(), mimetype='text/csv') 

where going wrong?

http://flask.pocoo.org/docs/0.10/patterns/streaming/#streaming-with-context

pretty explains how keep context around