Returns a list of the visible column names for this widget.
        
        :return     [<str>, ..]

def visibleColumns(self):
        """
        Returns a list of the visible column names for this widget.
        
        :return     [<str>, ..]
        """
        return [self.columnOf(c) for c in range(self.columnCount()) \
                if not self.isColumnHidden(c)]