register:

@app.route(‘/login’,    methods=[‘GET’, ‘POST’])

def login():

”’  Logs    in  a   user.   ”’

error   =   None

if request.method   ==  ‘POST’:

db  =   get_db()

try:

query   =   ‘select id  from    users   where   name    =   ?   and password    =   ?’

id  =   db.execute(query,   (request.form[‘username’],

request.form[‘password’])).fetchone()[ 0 ]

#   fails   if  record  with    provided    username    and password

#   is  not found

session[‘logged_in’]    =   True

flash(‘You  are now logged  in.’)

app.config.update(dict(USERNAME=request.form[‘username’]))

return redirect(url_for(‘show_entries’))

except:

error   =   ‘User   not found   or  wrong   password.’

return render_template(‘login.html’,    error=error)

Once users have registered or logged in again, they should be able to add comments in the

chat room. The function add_entry stores the comment text, the username of the user who

commented, and the exact time (to the second) of the posting. The function also checks

whether the user is logged in or not:

@app.route(‘/add’,  methods=[‘POST’])

def add_entry():

”’  Adds    entry   to  the TC  database.   ”’

if not session.get(‘logged_in’):

abort( 401 )

db  =   get_db()

now =   dt.datetime.now()

db.execute(‘insert  into    comments    (comment,   user,   time)   values  (?, ?,  ?)’,

                                                [request.form[‘text’],  app.config[‘USERNAME’], str(now)[:- 7 ]])

db.commit()

flash(‘Your comment was successfully    added.’)

return redirect(url_for(‘show_entries’))

Finally, to end the session, the user must log out. This is what the function logout

supports:

@app.route(‘/logout’)

def logout():

”’  Logs    out the current user.   ”’

session.pop(‘logged_in’,    None)

flash(‘You  were    logged  out’)

return redirect(url_for(‘show_entries’))

If we want to run the Python script as a standalone application we should add the

following lines, which make sure that a server is fired up and that the application is

served:

#   main    routine

if __name__ ==  ‘__main__’:

init_db()       #   comment out if  data    in  current

#   TC  database    is  to  be  kept

app.run()

Putting all these pieces together, we end up with the Python script shown as Example 14-

2.

Example 14-2. Python script embodying the core of the Tradechat application

Tradechat

A simple example for a web-based chat room

based on Flask and SQLite3.