app.py

from flask import Flask, redirect, render_template, request, session, url_for

app = Flask(__name__)
app.secret_key = (
    "AddYourSecretKeyHere"  # See the README.md file for instructions
)

PLACEHOLDER_CODE = "print('Hello, World!')"


@app.route("/", methods=["GET"])
def code():
    if session.get("code") is None:
        session["code"] = PLACEHOLDER_CODE
    lines = session["code"].split("\n")
    context = {
        "message": "Paste Your Python Code 🐍",
        "code": session["code"],
        "num_lines": len(lines),
        "max_chars": len(max(lines, key=len)),
    }
    return render_template("code_input.html", **context)


@app.route("/save_code", methods=["POST"])
def save_code():
    session["code"] = request.form.get("code")
    return redirect(url_for("code"))


@app.route("/reset_session", methods=["POST"])
def reset_session():
    session.clear()
    session["code"] = PLACEHOLDER_CODE
    return redirect(url_for("code"))