= A simple example =

Here's a simple example of how we could use Albatross Forms to collect a username and password from the user.

We need to define a model class to hold the data:

{{{#!python
import pwd, crypt

class User:
    def __init__(self, username, password):
        self.username = username
        self.password = password

    def is_password_valid(self):
        try:
            pw = pwd.getpwnam(self.username)
        except KeyError:
            return False
        return (crypt.crypt(self.password, pw.pw_passwd) == pw.pw_passwd)
}}}

Next, we need to define a form to display the fields:

{{{#!python
from albatross.ext.form import *

class LoginForm(FieldsetForm):
    def __init__(self, user):
        fields = (
            TextField('Username', 'username'),
            PasswordField('Password', 'password'),
        )
        fieldsets = (Fieldset(fields), )
        buttons = Buttons((
            Button('Login', 'login'),
        ))
        FieldsetForm.__init__(self, 'User login', fieldsets, buttons=buttons)
        
        self.load(user)
}}}

We need to create an instance of the Login model and maintain that so that any captured data is retained.  In our {{{login.py}}}, we use:

{{{#!python
def page_enter(ctx):
    if not ctx.has_value('user'):
        ctx.locals.user = User('', '')
        ctx.add_session_vars('user')
        ctx.locals.login_form = LoginForm(ctx.locals.user)
        ctx.add_session_vars('login_form')
    ctx.locals.login_error = ''
}}}

In {{{login.html}}}, to display the form to the user we use:

{{{#!html
<al-form method="post">

  <alx-form name="login_form" errors />

  <al-expr expr="login_error" />

</al-form>
}}}

When the user presses the "Login" button, it will come back to our {{{page_process}}} method in {{{login.py}}}.  We check if the username and password are correct and punt them into the application proper (via the "search" page) or tell them they've got it wrong.

{{{#!python
def page_process(ctx):
    if ctx.req_equals('login'):
        # nothing to validate
        ctx.locals.login_form.merge(ctx.locals.user)
        if ctx.locals.user.is_password_valid():
            ctx.redirect('search')
        else:
            ctx.locals.login_error = 'Login incorrect'
}}}