Make field readonly / display or hide a field in Odoo / OpenERP conditionally

Make a field read-only or visible based on another field value in Odoo / Openerp
Ex1: Hide field field1 when field2 has no data

<field name="field1" attrs="{'invisible':[('field2', '!=', False)]}"/>

Ex2: Hide field field1 when field2 has no data:
<field name="field1" attrs="{'readonly':[('field2', '!=', False)]}"/>