Example of download excel file with Buffer

app.py

import openpyxl
from openpyxl import load_workbook
from io import BytesIO
from flask import Flask, jsonify, Response

app = Flask(__name__)


@app.route("/")
def index():
    return jsonify({"message": "Hello World"})


@app.route("/download")
def download():

    # Would be coming from DB.
    data = [
        {"name": "John", "age": "26", "city": "New York"},
        {"name": "Steward", "age": "27", "city": "New York"},
        {"name": "Frank", "age": "28", "city": "New York"},
    ]

    wb = load_workbook("template.xlsx")
    ws = wb["overview"]
    h = 5
    for i in data:
        ws[f"B{h}"].value = i["name"]
        ws[f"C{h}"].value = i["age"]
        ws[f"D{h}"].value = i["city"]
        h += 1

    buffer = BytesIO()
    wb.save(buffer)
    headers = {"Content-Disposition": "attachment; filename=output.xlsx", "Content-type": "application/vnd.ms-excel"}
    return Response(buffer.getvalue(), headers=headers)


if __name__ == "__main__":
    app.run(host="0.0.0.0", port=5000, debug=True)