Safer to use the reference to the public user instead of hardcoding its id.

if request.env.user.id == request.env.ref('base.public_user').id:
    return request.render('web.login', {})

hi,
you can use request.session.uid or env.context.get('uid')

Hello,

This could be done with this code snippet inside a web controller: (Tested on Odoo 8)

public_user = http.request.env['res.users'].sudo().search([('id', '=', 3),('active', '=', False)]) # Public user default ID
if request.uid == public_user.id:
     # The user is logged in
     # Put your code for logged in user here
else:
    # The user is not logged in
    # Put your code for public users here

Regards,

Slim BHIRI