title: What is the UserMixin in Flask?
body: <pre class="lang-py prettyprint-override"><code>from datetime import datetime
  from werkzeug.security import generate_password_hash
  from werkzeug.security import check_password_hash
  from flask_login import UserMixin
  from app import db
  
  
  class User(UserMixin, db.Model):
      id = db.Column(db.Integer, primary_key=True)
      username = db.Column(db.String(64), index=True, unique=True)
      email = db.Column(db.String(64), index=True, unique=True)
      password_hash = db.Column(db.String(64))
      posts = db.relationship('Post', backref='author', lazy='dynamic')
  
      def set_password(self, password):
          self.password_hash = generate_password_hash(password)
  
      def check_password(self, password):
          return check_password_hash(self.password_hash, password)
  
      def __repr__(self):
          return '&lt;User{}&gt;'.format(self.username)
  
  </code></pre>
  <p>After reading <a href="https://flask-login.readthedocs.io/en/latest/#your-user-class" rel="noreferrer">the official documentation</a> I couldn't yet understand the purpose of <code>UserMixin</code>. Can anyone please describe it in brief?</p>