10. session.py

# coding:utf-8



from flask import Flask, session, redirect, url_for, escape, request
app = Flask(__name__)
app.secret_key = "lololol"

@app.route('/')
def index():
    
    if 'username' in session:
        username = session['username']
        return 'logged in as ' + username + \
            "<b><a href = '/logout'>click here to log out</a></b>"
    
    return "You are not logged in <br><a href = '/login'></b>" + \
      "click here to log in</b></a>"

@app.route('/login', methods = ['GET', 'POST'])
def login():
   if request.method == 'POST':
      session['username'] = request.form['username']
      return redirect(url_for('index'))
   return '''
   <form action = "" method = "post">
      <p><input type = text name = username/></p>
      <p><input type = submit value = Login/></p>
   </form>
   '''

@app.route('/logout')
def logout():
   # remove the username from the session if it is there
   session.pop('username', None)
   return redirect(url_for('index'))

if __name__ == '__main__':
    app.run()