Python

Someone shared me this code pls explain : from flask import Flask, render_template, request, redirect, url_for, flash, session, abort from flask_sqlalchemy import SQLAlchemy from flask_wtf import FlaskForm from wtforms import StringField, PasswordField, TextAreaField, SubmitField from wtforms.validators import DataRequired, Length from passlib.hash import bcrypt from datetime import datetime app = Flask(name) app.config['SECRET_KEY'] = 'replace-this-with-a-secure-random-string' app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///progsite.db' app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False db = SQLAlchemy(app) # ---------- Models ---------- class User(db.Model): id = db.Column(db.Integer, primary_key=True) username = db.Column(db.String(80), unique=True, nullable=False) password_hash = db.Column(db.String(255), nullable=False) is_admin = db.Column(db.Boolean, default=False) def verify_password(self, password): return bcrypt.verify(password, self.password_hash) class Problem(db.Model): id = db.Column(db.Integer, primary_key=True) title = db.Column(db.String(200), nullable=False) statement = db.Column(db.Text, nullable=False) sample_input = db.Column(db.Text, default='') sample_output = db.Column(db.Text, default='') created_at = db.Column(db.DateTime, default=datetime.utcnow) class Submission(db.Model): id = db.Column(db.Integer, primary_key=True) user_id = db.Column(db.Integer, db.ForeignKey('user.id')) problem_id = db.Column(db.Integer, db.ForeignKey('problem.id')) code = db.Column(db.Text, nullable=False) verdict = db.Column(db.String(50), default='Pending') created_at = db.Column(db.DateTime, default=datetime.utcnow) user = db.relationship('User', backref='submissions') problem = db.relationship('Problem', backref='submissions') # ---------- Forms ---------- class RegisterForm(FlaskForm): username = StringField('Username', validators=[DataRequired(), Length(min=3, max=80)]) password = PasswordField('Password', validators=[DataRequired(), Length(min=6)]) submit = SubmitField('Register') class LoginForm(FlaskForm): username = StringField('Username', validators=[DataRequired()]) password = PasswordField('Password', validators=[DataRequired()]) submit = SubmitField('Login') class ProblemForm(Flask