download a rendered template as a StringIO object in a Flask app

app.py

from StringIO import StringIO

from flask import Flask, render_template, send_file

app = Flask(__name__)


@app.route('/bootstrap')
def bootstrap():
    str_io = StringIO()
    str_io.write(render_template('files/bootstrap.sh.j2'))
    str_io.seek(0)
    return send_file(
        str_io,
        attachment_filename='bootstrap.sh',
        as_attachment=True
    )