<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _update_lock_icon(self):

 """Update locked state icon"""

        icon = ima.icon('lock') if self.locked else ima.icon('lock_open')
        self.locked_button.setIcon(icon)
        tip = _("Unlock") if self.locked else _("Lock")
        self.locked_button.setToolTip(tip)