what i want to do in my custom form that is on image preview ...
what i have done .....
in Py
tz  = fields.Selection('_tz_get', string='Timezone', required=True,                                default=lambda self: self.env.user.tz or 'UTC')
in XML
<field name="tz"/>
Error is 
object has no attribute '_tz_get'
any solution please
