Hi i want to validate a field prefix, when i enter a website in a field like (jothimani.com), here i want show error (Please enter valid Website address ex: www.jothimani.com here is my code...

in xml

<record id="view_employee_form" model="ir.ui.view">
    <field name="name">jebatraining.form_view</field>
    <field name="model">employee_data</field>
    <field name="type">form</field>
    <field name="arch" type="xml">
        <form string="Employee Details">
            <field name="website" string="Website"/>
        </form>
    </field>
 </record>

in py

class jebatraining(osv.osv):
    _name = "employee_data"
    _description = "Employee management"
    _columns = {
        'website':fields.char('Website', size=50, required=True),

        }
jebatraining()

hi anyone help me to know what can i do here?