'verifies if check_in is earlier than check_out.'

@api.constrains('check_in', 'check_out')
def _check_validity_check_in_check_out(self):

    for attendance in self:
        if (attendance.check_in and attendance.check_out):
            if (attendance.check_out < attendance.check_in):
                raise exceptions.ValidationError(_('"Check    Out"    time    cannot    be    earlier    than    "Check    In"    time.'))
