app.py

from flask import Flask, render_template, request
import os

app = Flask(__name__)

FILE_NAME = "data.txt"

# create file if not exists
if not os.path.exists(FILE_NAME):
    open(FILE_NAME, "w").close()


@app.route("/")
def home():
    return render_template("index.html")


@app.route("/operate", methods=["POST"])
def operate():

    text = request.form.get("text")
    operation = request.form.get("operation")

    if operation == "write":
        with open(FILE_NAME, "w") as f:
            f.write(text + "\n")

    elif operation == "append":
        with open(FILE_NAME, "a") as f:
            f.write(text + "\n")

    elif operation == "read":
        with open(FILE_NAME, "r") as f:
            text = f.read()

    else:
        text = "Invalid operation"

    return render_template("index.html", result=text)


if __name__ == "__main__":
    app.run(host="0.0.0.0", port=7860)